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Herbicidal WeedControl Methodsfor Pastures andNatural Areasof Hawaii
Philip Motooka1, Lincoln Ching2, and Guy Nagai3
1,2CTAHR Departments of 1Natural Resources and Environmental Management and 2Human Nutrition, Food and Animal Sciences3Hawaii Department of Agriculture
Weed ControlNov. 2002—WC-8
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Herbicidal Weed Control Methods for Pastures and Natural Areas of Hawaii
Methods of weed control ............................................ 3Quarantine and sanitation ........................................ 3Biocontrol ................................................................ 4Cultural control ....................................................... 4Mechanical or manual control ................................. 4Herbicides................................................................ 5Herbicide hazards in perspective............................. 5
Methods of herbicide application ............................... 6
Conventional foliar methods ................................... 6Choice of herbicide .............................................. 6Herbicide selectivity ............................................ 7Herbicide persistence ........................................... 7Herbicide formulations ........................................ 7Surfactants ............................................................ 8Rates of application .............................................. 8Coverage .............................................................. 8Spray volume rates ............................................... 8Timeliness ............................................................ 9Integrated treatments ............................................ 9Drift prevention .................................................. 10Calibration of spray volume rate and
herbicide concentration ............................... 10Boom sprayer .................................................. 11Power sprayer, orchard gun method ............... 11Knapsack sprayer ............................................ 11
Drizzle foliar application ....................................... 12
Logistics limit conventional spraying ................ 12The drizzle method ............................................ 12Efficiency of the drizzle method ........................ 14Other advantages ................................................ 14Limitations of the drizzle method ...................... 14Calibration .......................................................... 14Table 1. Herbicides for drizzle application ........ 15Drizzle foliar application, water carrier ............. 16Drizzle foliar application, crop oil carrier .......... 16
Cut-surface methods .............................................. 16Notching ............................................................. 16Cut-stump method .............................................. 18Basal bark method .............................................. 19Very-low-volume basal bark and
stump applications .......................................... 20
Soil-applied herbicides .......................................... 20
Appendix 1. Herbicides registered for use inpastures and natural areas of Hawaii ................. 23
Table A-1. The rating scale of toxins andexample substances ............................................ 25
Table A-2. Pesticide toxicity signal words andapproximate lethal dose ..................................... 25
Appendix 2. Common and botanical names ofweeds mentioned in the text .................................. 32
Literature cited .......................................................... 33
Table of Contents
AcknowledgmentsMany colleagues participated in the field work that gener-ated the information presented here. Many hours of work inthe hot sun or pouring rain are represented in a single recom-mendation. From the UH CTAHR Cooperative ExtensionService: Mike DuPonte and Andrew Kawabata, Hilo; GlenFukumoto, Kona; John Powley, Maui; Alton Arakaki andGlenn Teves, Molokai. From the Hawaii Department of Ag-riculture: Guy Nagai (retired), Kauai; Kyle Onuma and WayneShishido (retired), Hilo. From the Hawaii Department of Landand Natural Resources, Division of Forestry and Wildlife:Ed Pettys, Alvin Kiyono, Craig Koga, Galen Kawakami, andSanford Soto, Kauai; Glenn Shishido and Fern Duvall, Maui.
Many others in both the public and private sectors par-ticipated occasionally. Many ranchers and other landown-ers and land managers allowed access to their lands.DowAgrosciences, DuPonte De Nemours, American Cy-
anamid, BASF, Monsanto, PBI Gordon, United HortculturalSupply, and Brewer Environmental Industries furnishedneeded supplies. Drs. Roy Nishimoto and J.B. Friday(CTAHR) ably reviewed the manuscript, and Dale Evansedited and produced the finished publication. Finally, thecontribution of funds to publish this document was gener-ously provided by several organizations: the Institute ofPacific Islands Forestry, Forest Service, U.S. Departmentof Agriculture; the Big Island Invasive Species Committeeand the Division of Forestry and Wildlife of the HawaiiDepartment of Land and Natural Resources; the U.S. Na-tional Park Service Pacific Islands Exotic Plant Manage-ment Team and the Maui Invasive Species Committee; theUSDA Natural Resources Conservation Service and the Eastand West Kauai Soil and Water Conservation Districts. Allof these contributions are gratefully acknowledged.
Neither the University of Hawaii, the College of Tropical Agriculture and Human Resources, nor the authors shall be liable for any damagesresulting from the use of or reliance on the information contained in this publication, or from any omissions to it. Mention of a trademark, company,or proprietary name does not constitute an endorsement, guarantee, or warranty by the University of Hawaii Cooperative Extension Service or itsemployees and does not imply recommendation to the exclusion of other suitable products or companies. Pesticide use is governed by state andfederal regulations. Read the pesticide label to ensure that the intended use is included on it, and follow all label directions.
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The severity of the impact of weeds on ranching andforest management is often underestimated. Besides
competing with forage plants for soil nutrients, sunlight,and water, and thereby suppressing forage growth, weedsalso create management problems.
For example, brush in Texas used up over two timesthe water requirements of all the cities and industries inthat state in 1980(32). Many weeds are poisonous, orarmed with spines that may injure animals directly orby leading to infections. Mesquite (Prosopis spp.) in-festations in Arizona suppressed forage growth and pro-moted soil erosion and rain runoff(66). On brush-infestedranches, cattle are more skittish, requiring more laborto manage; more bulls are required to service the herd;newborn calves instinctively remain in hiding as mow-ers approach and may be killed. Another Texas studyindicated that brush-free ranches could stock 42 percentmore animals and would need 59 percent less perma-nent labor and 58 percent less labor at roundup(34). Weedsalso threaten native plant communities in forests andshrublands and, thereby, the native animals dependenton the specific native plants or complex of plants thatmake up that plant community. The original ecosystemis thus replaced by a new, exotic one(10).
Weeds are often more competitive than native plantsbecause of a lack of natural controls such as diseasesand predators. Many are able to suppress plants grow-ing close to them by producing growth retardants. Indi-rectly, they suppress natives by supporting wildfires,which may be devastating to native plants but whichmay be natural to alien species; they may fix nitrogen,which alien species may be better able to utilize thannatives(102). The ecology of natural areas worldwide isthreatened by invasive weeds. Thus weed management
is an on-going problem for ranchers, foresters, and otherland managers.
Use of herbicides is an effective and efficient meansof managing weeds. Contrary to popular perception, itis also very safe. In many cases there are no practicalalternatives to chemical weed control methods. How-ever, herbicides can easily be misused and inflict unin-tended injury to non-target organisms. In order to en-sure efficacy, efficiency, and economy—and non-targetsafety—users of herbicides must have an understand-ing of herbicide application principles and plant re-sponses to herbicides.
Methods of weed controlPrehistoric humans saw the need to deal with weeds.Nearly 3000 years ago, people in Europe cleared treesand brush from around oak and nut trees to increase thesize and number of acorns and nuts(21). Throughout his-tory, many methods of control have been devised, all ofwhich are still used today. While this publication dealswith chemical methods of weed management, one ormore of the other methods are often used in conjunctionwith chemical methods. Several of these methods re-quire the authority and resources of the government (e.g.,quarantine and biocontrol). Others are in the hands ofthe herbicide user (e.g., mechanical methods). Becausean understanding of the other methods can be helpful indeveloping comprehensive weed management strategies,they are briefly described in the following paragraphs.
Quarantine and sanitationThe most economical method of weed control is pre-vention. Weed species are prevented from moving intouncontaminated areas by quarantine, the official regu-
Herbicidal Weed Control Methodsfor Pastures and Natural Areas of Hawaii
Philip Motooka, Lincoln Ching, and Guy Nagai
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lation of weed movement across political borders, andby sanitation, the unofficial control of weed movement(e.g., cleaning shoes and clothing between hikes andcorraling livestock for a time between infested pasturesand uninfested pastures). Unfortunately, with increas-ing worldwide commerce, preventing weed movementis becoming more difficult. New weeds and other pestsdo get by quarantine, either deliberately or inadvertently.
One of the problems is that weediness is unpredict-able. A noxious weed in one area can be benign in an-other. A further difficulty is that many alien plant intro-ductions may be benign for years or decades before sud-denly exploding into a serious weed pest(17). There areongoing attempts to characterize weediness so that quar-antine can be made more effective and efficient. It hasbeen suggested that some of the characteristics that de-termine weediness include short cycles between seedings,production of many seeds, small seeds, seed dispersal byvertebrates, adaptation to a large latitudinal range, andabsence of the alien genus in the invaded area. The USAand most of the world maintain “dirty lists” of prohibitedplants. Australia and New Zealand maintain a “clean list”of plants that are allowed to be imported; everything noton the list is prohibited(17). These two countries require astrict protocol for importing prohibited plants for researchand possible development into commercial crops. In ei-ther approach, knowledge of what makes a plant a weedhelps in formulating quarantine lists(17). Every noxiousweed kept out of Hawaii means economic losses and en-vironmental damage avoided and a great deal of moneyand effort not required to deal with that weed.
BiocontrolWeed biocontrol is the suppression of weeds by insectsand microorganisms that feed on the target plants or oth-erwise parasitize them. Hawaii has been a pioneer inclassical biocontrol of weeds; i.e., biocontrol in whichthe biocontrol agent is able to sustain itself after releaseinto the environment. The Board of Agriculture andForestry began biocontrol work in the early 1900s. Earlysuccesses against lantana and prickly pear cactus andmore recent success with Hamakua pamakani and Mauipamakani resulted from these efforts(38) (see AppendixII for botanical names of weeds of Hawaii). While suc-cessful biocontrol is extremely economical, success isnot assured. Efforts on gorse, faya tree, christmasberry,and others have not been fruitful so far. Furthermore,success may not be complete. Lantana is still a seriousproblem over large areas. In addition, because biocontrolis species-specific and there are a couple of hundredserious weed species and only limited resources to do
the exploratory, safety, and efficacy research, biocontrolhas to focus on only a few of the most serious weeds.Recently there has been interest in mycoherbicides,pathogenic fungi that are sprayed onto weeds, but incontrast to classical biocontrol, these fungi are unableto persist in the environment and die out with the weed.
Cultural controlCultural control includes those management practicesthat modify the agroecosystem to make the pasture, crop,or forest ecosystem resistant to weed establishment and,at the same time, support overall economic goals. Ex-amples include fertilizing pastures to provide not onlygreater yields but also quicker and denser ground cover;managing livestock using intensive grazing managementsystems(101) in which pastures are intensively grazed forshort periods, allowing grazing to refresh the forage andtrampling to suppress the weeds, followed by a longerrest period for grass recovery; and integrating sheep orgoats to browse brush species and fowl to graze herbsand grasses(90). Some reasonably call the use of livestockin weed management biocontrol, but the difference isthat livestock husbandry is a form of production agri-culture, whereas the use of invertebrates or microbes isa specific weed management tactic.
Mechanical or manual controlPrior to the development of modern herbicides, ranchand forest managers relied mainly on mechanical meth-ods of weed control, such as grubbing, bulldozing, drag-ging, cabling, and mowing. Ranchers used to pull weedsout of the ground with tractors or grub them out withhand tools. These methods were expensive, injurious toforage species, and ineffective over the long term. Heavyequipment exposed the soil to erosion and brought largerocks to the surface, which thereafter hindered mobilityof horses and equipment. Another serious drawback ofmechanical methods of weed control was that they werelabor-intensive and therefore slow. Ranchers did not haveenough slack periods to divert sufficient manpower tocontrol all the weeds on the ranch in a timely manner.The demands of other tasks, equipment breakdowns,rains, and soggy grounds often precluded operations onparts of the ranch. Steep terrain or rocky ground alsohindered weed control operations. Weed control deferredresulted in a more difficult task later.
The most serious aspect of mechanical control is itshazards. Agriculture is a very dangerous occupation,recording 50 deaths per 100,000 workers per year against11 per 100,000 per year for all industries combined(70).In 1993, there were 130,000 agricultural work-related
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injuries and 1100 deaths(27). Tractor rollovers are espe-cially dangerous, accounting for 15–25 percent of farmdeaths. Although the data do not so specify, some ofthese accidents and deaths undoubtedly occurred dur-ing weed control operations. Because mechanical con-trol suppresses weed growth only for short periods, fre-quent retreatments are required, increasing worker con-tact with dangerous equipment.
Weeds germinate from an inexhaustible seed sup-ply in the soil, or they resprout from stumps, roots, orstem fragments. In high-rainfall areas, new flushes fromcut stumps of some species can grow 3–4 ft tall in 3months. Mechanical methods are often used in pasturesand forests, primarily where the weeds, especially woodyor other large plants, must be cleared immediately ei-ther for aesthetics or safety, or as a pretreatment to her-bicide applications.
HerbicidesCompared to mechanical weed control methods, herbi-cides provide greater efficacy at lower cost. Properlymanaged, herbicides provide relatively long term weedcontrol. Spraying equipment is generally cheaper topurchase and operate than the heavy equipment used inmechanical weed control. Chemical weed control ismuch more rapid and provides longer term weed sup-pression than mechanical methods. Furthermore, herbi-cidal weed control results in greater grass production inpastures than does clipping of weeds(18). Chemical meth-ods reduce labor costs, provide greater flexibility in themanagement of labor and, most importantly, reduce therisk of accidents by reducing fatigue and worker expo-sure to power equipment and sharp implements.
For large tracts of land, aerial applications can beextremely cost-efficient, with costs per unit area as muchas a tenth the cost of ground applications. Aerial appli-cations can cover hundreds of acres per day, versus 5–75 acres per day with ground equipment. Moreover,aerial applications can be made on rough terrain andsoggy soils where ground rigs cannot operate.
It is commonly perceived that a single herbicide ap-plication can solve any weed problem and that herbicidesare extremely toxic. Neither is true. Properly used, herbi-cides can reduce weed populations quickly and selectively,and thereby provide immediate increases in grass pro-duction in pastures or native plant growth in forests. How-ever, even under the best of circumstances, herbicideswill not eradicate widely established weeds. Herbicidesoffer suppression of weed populations quickly and forlonger periods than mechanical control methods.
However, herbicides alone are not the answer to
weed problems. Indeed, effective weed management canseldom be achieved by a single method or action. Her-bicides provide a means to suppress or even eliminatestanding weeds. However, it cannot prevent re-infesta-tion except by repeated application, unless managementpractices (e.g., fertilizer application, grazing) or ecologi-cal conditions are changed (e.g., biological control, es-tablishment of a canopy of desirable plants, exclusionof ungulates) to exert more pressure on the weed popu-lation. Herbicides are a management tool, effective andsafe if used properly.
Herbicide hazards in perspectiveThere is a great deal of concern about the health hazardsof pesticides, including herbicides, that is a source ofneedless anxiety. To be sure, some pesticides are ex-tremely toxic (acute toxicity) and do require commen-surately extreme precautions in their handling and man-agement, as is required with any toxic substance. Fortu-nately, most herbicides are not highly toxic, and mostserious cases of poisoning have been the result of thevictims swallowing one of the more toxic chemicalsrather than from unavoidable exposure during normaluse or through consumption of foods derived fromtreated crops. As in all occupations, constant educationand training are required to reduce exposure to hazardsand to deal with emergencies.
Perhaps the greater perceived threat in the publicmind is that pesticide residues in food, air, and waterincrease the risk of diseases, especially cancer (chronictoxicity). The source of this concern, however, is ani-mal tests in which massive doses are administered tosusceptible animals. Using assumptions that greatly ex-aggerate human susceptibility and exposure to pesticides,these data are then converted to lifetime risks to humans.These assessments are often misunderstood as represent-ing predictions or even realized casualties. Confusion iscompounded by the language of risk assessment, inwhich risks are expressed as numbers of human illnessespesticides will supposedly cause.
Toxicologists are almost unanimous in the view thatanimal tests are inappropriate for determining actual risksto humans(2, 4, 85, 99, 116). After 60 years of pesticide use,during the first decades of which regulations were notas stringent as they currently are, age-adjusted cancerrates have not changed, except for lung cancer, whichhas soared, and stomach cancer, which has declined(29).Research(30) reviewing human epidemiological studieshas concluded that pesticides are “unimportant” as acause of cancer; that the real causes of cancer were morea matter of lifestyle (diet, smoking, exposure to sun-
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light) than environmental pollutants.In the USA the average life span, an indicator of
public health, has been steadily increasing in the face ofwidespread pesticide use, to the point that the averagenow approaches the maximum human life span. Fur-thermore, dozens of naturally occurring chemicals infoods (e.g., vitamin A), including fruits and vegetables,were carcinogenic in laboratory tests, and these addedup to 10,000 times the amount of pesticides residues infoods(4, 104). Even that may be underestimated by a factorof 10(105). At current levels of synthetic chemical resi-dues, one would consume only 0.1 oz of synthetic chemi-cal residues from foods in an 80-year lifetime(3, 37) andanother 0.1 oz from drinking water(9). Not all of theseresidues would be pesticides or laboratory carcinogens.In the same lifetime, one would consume 97 lb of natu-ral carcinogens. Evidence also indicates that fruits andvegetables in diets, despite their natural carcinogeniccomponents, actually prevent cancer(30) because they alsocontain high levels of anticarcinogens(2). Thus pesticidemisinformation and scares cause more harm than goodif they cause people to avoid fruits and vegetables forfear of the pesticide residues they may contain. Ratherthan poisoning our food, pesticides have helped to pro-vide the most bountiful and wholesome food supply inhistory. In light of the available evidence, the prudentcourse recommended by health scientists is not to dis-avow use of pesticides but to use them appropriately.
Methods of herbicide applicationTo attain the most economical and effective chemicalweed control with minimal untoward environmental ef-fects, herbicides must be properly managed, not appliedhaphazardly to the weeds. Based on the weeds to becontrolled and the particular situation at hand, the usermust determine the method of application, the herbi-cide, rate, and time of application. There are severalmethods of herbicide application, each with its own par-ticular advantages and utility.
Conventional foliar methodsThe most common herbicide application method is fo-liar application by spraying (Figure 1). It is the easiestand most economical method of applying herbicides.Herbicides can be applied with knapsack sprayers, powerequipment, or by aircraft. In addition, recent innovationshave made possible very-low-volume and ultra-low-volume applications and wipe-on systems.
Choice of herbicideThe user should choose, from among the herbicides reg-istered for the intended use, the herbicide best suited tothe particular goals of efficacy, economy, and environ-mental protection. Obviously, the herbicide must be ef-fective on the target weeds. Certain weeds are more sen-sitive to one herbicide than to another or even to anotherformulation of the same herbicide. For example, 2,4-D
Figure 1. Foliar application of herbicide. Coverage of the entire canopy, not drenching, is critical.
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is effective on many herbaceous broadleaves but is weakon most woody plants. Legumes (Fabaceae) such ascatsclaw and hilahila and composites (Asteraceae) suchas tropic ageratum and ragweed parthenium are gener-ally very susceptible to picloram, triclopyr, and clo-pyralid, while the mustards (Brassicaceae) are tolerantof these herbicides. The polygonaceous weeds (spineyemex, kamole) are extremely sensitive to dicamba. Mostbroadleaves are more sensitive to 2,4-D ester than to theamine salt formulation.
Typically, a given weed species will be susceptibleto more than one herbicide. Other things being equal,the lower-cost herbicide should be used. However, indetermining the cost, the cost per acre, and not the costper gallon, should be considered. For example, catsclawcan be controlled with 0.2 lb picloram active/acre. There-fore, one gallon of picloram (2 lb/gal) is sufficient totreat 10 acres of catsclaw. Even though picloram maycost $100 per gallon, it would be cheaper than a herbi-cide costing $50 per gallon that can treat only 2 acres ofcatsclaw ($10/acre vs. $25/acre).
Other considerations also affect the choice of herbi-cide. Continued use of a single herbicide over time canresult in shifts of weed populations toward species thatare naturally tolerant of that herbicide. Also, weed spe-cies initially susceptible to a herbicide may develop re-sistance to that herbicide if it is used repeatedly overtime. Resistance usually takes many years to develop,but sulfonylureas (e.g., metsulfuron) and imidazolinones(e.g., imazapyr) have triggered resistance in certainweeds in as few as four years. Over-reliance on any her-bicide in these two families will result in resistance toall herbicides in both families(52, 65, 92). Rotation of meth-ods of weed control and herbicides will help to preventweed population shifts and buildup of resistance.
To prevent contamination of groundwater and sur-face water bodies, the applicator should avoid or reducethe use of persistent, soil-mobile herbicides in high-rain-fall areas.
Herbicide selectivityHerbicides are “selective” if they kill or injure certainplants but not others, e.g., dicots (broadleaf plants) butnot monocots (such as grasses). Herbicides are “nonse-lective” if they kill or injure all plants to which they areapplied. Selectivity allows the convenience of broad-cast applications. However, herbicides effective againstbroadleaf weeds also kill desirable legumes. Heavy graz-ing to defoliate forage legumes before spraying, or us-ing a different formulation (e.g., 2,4-D amine instead ofester), may allow the legumes to escape serious injury.
Spot spraying or other directed application proceduresmay also protect forage legumes. There are a number ofgrasskillers (e.g., fluazifop) that can be used where di-cots need to be protected.
Herbicide persistenceHerbicides that are readily detoxified in the soil are “non-persistent” and those that resist breakdown are “persis-tent.” Persistent herbicides provide long-term weed con-trol. However, if legumes in pastures or natives plantsin forests are to be planted into an area after herbicidetreatment, persistent herbicides may injure seedlings ofsuch plants. Thus the choice of a herbicide may dependon the need for longer-term suppression on the one handand the residual toxicity to desirable plants on the other.
Herbicide formulationsSome herbicides are available in hydrophilic (water lov-ing or water soluble) or lipophilic (oil loving or oilsoluble) formulations; 2,4-D and triclopyr are availablein both types of formulation. Commonly, the hydrophilicformulations are amine salts and the lipophilic formula-tions are emulsifiable esters. Both types of formulationmay be applied with water. The amine salts form truesolutions with water, and the esters form an emulsion.The solution is clear, the emulsion is milky. The emul-sion, micro-droplets of oily substance suspended inwater, must be agitated occasionally to keep the herbi-cide formulation and water from separating in the tank.In general, esters are more effective than salts becausethe oily nature of esters allows them to adhere to andpenetrate the waxy cuticle of leaves better than salts.Esters therefore are better in situations where rain islikely to occur shortly after the herbicide application,because they enter the plant quickly and resist beingwashed off the leaves by rain.
Esters are more volatile than amine formulations.Esters can volatilize from the spray droplets and fromthe plant and soil surfaces. The volatilized herbicide canthen be carried with air movement to injure sensitivecrops and other nontarget plants downwind. This is called“vapor drift,” in contrast to “spray drift,” which is themovement of the spray droplets or solid particles. Mod-ern ester formulations are “low volatile” but may stilldrift if improperly managed (e.g., applied with a mistblower). Where wind direction is unfavorable, tempera-ture is likely to be high, and sensitive plants are near, itwould be safer to use a non-volatile product. Volatiliza-tion of esters can also reduce herbicide efficacy on hotdays by reducing the effective rate(22, 100). For basal barkapplications (to be discussed later), oil-soluble formu-
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lations are essential to the efficacy of the method.
SurfactantsSurfactants, a coined term for “surface-active agents,”are chemicals that change the physical properties of liq-uid surfaces. Surfactants, depending on the chemical orblend of chemicals used, can act to enhance emulsifica-tion, dispersal, wetting, spreading, sticking, and leaf-penetration of the solution(8). Although soap and house-hold detergents are surfactants, they are not very effec-tive as agricultural surfactants and should not be usedfor that purpose. Surfactants aid the performance of her-bicides by• improving wetting of the weed; “wetting agents” or
“spreaders” enhance the spread of the spray dropletsand increase the area of contact between the dropletsand the leaf surface and, therefore, penetration of theleaf surface
• increasing resistance of the spray deposit to washingby rain (stickers); the longer the contact between theherbicide and the plant surface, the greater the amountof herbicide absorbed
• reducing the rate of drying of the spray deposit (hu-mectants); dry herbicides will not penetrate the leafsurface
• reducing the proportion of very fine droplets, thusreducing spray drift (drift retardants or thickeners)
• allowing the suspension of insoluble pesticides, i.e.,wettable powders, in water (emulsifiers).
Although reduction of surface tension of the spraydroplets is very important in increasing the efficacy ofherbicides, it is not the only means by which surfactantswork(97). Efficacy increases at surfactant concentrationsbeyond that which provides minimum surface tension(55),suggesting other mechanisms are at work. Surfactantsmay not be necessary when the plant is succulent, butthey can help with mature plants with hardened cu-ticles(59). The effects of surfactants vary. They generallyincrease uptake of herbicides and may increasetranlsocation but may sometimes decrease translocationby causing too severe injury to the target plant(15, 35, 84).
Rates of applicationHerbicide users should apply the recommended rate.Herbicide labels usually state the recommended rate interms of both amount of product and of “active ingredi-ent (a.i.)” or “acid equivalent (a.e.)” per acre. “Acidequivalent” is preferred for herbicides that are acids inthe parent form. “Active” is used in this publication tocover either of these terms, whichever is appropriate.
Overdosing is a common error as appliers, trying to get“better” or “quicker” or “once and for all” kill, may in-crease the herbicide concentration or the spray volumerate, or both. The result is unnecessary expense, unnec-essary release of herbicide into the environment, and,ironically, poor weed control.
Effective weed kill with systemic foliar herbicidesdepends on the herbicide being translocated from theleaves via the phloem into the stem and roots. Too higha rate will shut down the phloem too soon, before theherbicide can be translocated to sites of action(39, 51, 60, 62,
89). Even though treated woody plants might be quicklyand completely defoliated, they would recover quickly(12,
24, 86, 106). A rapid burning or defoliation may be spectacu-lar, but the effect is short-lived. Over the longer term,overdosing often results in much less kill of the weedpopulation than would the optimal, recommended rate.Foliar-applied systemic herbicides should cause a slowdecline of the target weed. The problem should be ap-proached as a long-term one requiring repeat annual orsemi-annual treatments at optimum rates until the weedpopulation is negligible. Thereafter, maintenance treat-ments with low rates of herbicide while the weeds aresmall are much more effective and efficient than wait-ing for the weeds to become a problem again.
CoverageThe importance of good coverage of the target plant withthe spray material cannot be overemphasized. Herbicidesin plants move readily longitudinally but very poorlyradially (horizontally). Thus, unless the herbicide is welldistributed over the plant canopy, control will be poor(31).Treating one side of the weed will result in injury to thatside only. Whether the herbicide is applied at a sprayvolume rate of 5 gal/acre or 80 gal/acre, good coverageis essential(88). Wetting per se is not important; it is onlya means to achieve good coverage. (This principle shouldnot be confused with the need of the spray material onthe foliage having to remain wet in order for the herbi-cide to penetrate the leaf cuticle[98].)
Spray volume ratesFor maximum efficiency as well as efficacy, spray vol-ume rates (spray volume per acre) must be kept as lowas possible while still allowing adequate coverage(58, 68,
103). Water is merely a diluent to make the herbicide sprayvolume large enough to make uniform distribution pos-sible. Any water beyond the minimum volume neededunnecessarily increases work by requiring more volumeto be sprayed and, thereby, more reloadings per acretreated. Fuel consumption and wear of equipment are
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unnecessarily increased. Efficacy is also reduced be-cause, at any given herbicide rate, dilute sprays are lesseffective than more concentrated sprays(1, 33, 67, 72, 94). Forthese reasons it is essential that herbicides be appliedprecisely.
Excessively high-volume application is usually theresult of• drenching by the applicator hoping to get better or
quicker weed kill• use of high pressure either to achieve drenching or
increase the reach (or “throw”) of the spray• a malfuctioning pressure regulator• dense brush that slows the speed of the sprayer.
TimelinessTimeliness of herbicide applications is critical to theeffectiveness of the herbicide and to the efficiency ofthe operation. Herbicide applications should be madewhen the weeds are most susceptible and when envi-ronmental conditions are suitable for effective and safeapplication. Herbicides should be applied under the fol-lowing conditions.
1. When energy reserves in the weeds are low(53).This is usually after plants have expended stored energyto fuel new growth, such as after a drought, after winter(at higher, colder elevations), after a fire, or after previ-ous herbicidal or mechanical treatments.
2. When there are some fully expanded, “soft”leaves(12, 31, 93). At this stage, the cuticle is thin, the leafarea is large enough to retain sufficient amounts of theherbicide spray, and, within the plant, downward trans-location is active as the weed begins to rebuild energyreserves (carbohydrates).
3. When the weeds are young. Small, young plantsare easier to control than larger, more mature, or woodierplants(64, 107, 112). Attacking weeds early in the infestationrequires less herbicide and fewer repeat treatments, af-fords greater mobility, and results in less weed competi-tion. In contrast, allowing weeds to grow too large com-plicates the weed control operation. Equipment move-ment is hindered by large, dense brush, particularly inrough terrain where unobstructed vision is critical. Re-duced speed tends to increase the spray-volume rate,because the sprayer output remains the same while theapplication speed is reduced. The greater mass of foli-age to be treated also means a higher spray volume ratemust be used to achieve complete coverage. Further-more, directing sprays upward to control tall plants in-creases the risk of herbicide drift. Timely retreatment,while the weeds are small, reduces the amount of herbi-cide needed in those subsequent treatments(57, 75).
4. When the weeds are actively growing. Weedsshould be sprayed when they are actively growing andphotosynthesizing. Actively growing plants have leavesthat are succulent and readily penetrable by herbicides.Foliar-applied herbicides must be translocated via thephloem out of the leaves and into storage sites in thestems and roots or to the growing points that need thecarbohydrates (photosynthate). Translocation in thephloem is “powered” by photosynthesis. Active photo-synthesis results in high photosynthate production in theleaves and active translocation of photosynthate via thephloem. Phloem-mobile herbicide absorbed by the leavesmoves with the flow of photosynthate. If photosynthe-sis is active, the flow of photosynthate and phloem-mobile herbicide is strong(11). If photosynthesis is weak,when the plant is diseased(111), for example, or while itis drought-stressed(14, 72), photosynthesis is weak and theflow of photosynthate and phloem-mobile herbicidedecreases or stops.
5. When it is not raining but soil moisture is ad-equate. Maximum uptake of herbicide from the leaf sur-face into the leaf is influenced by rain. Rainfall too soonafter application may wash the herbicide off the leaf sur-face(20, 23, 42, 117). The duration of the rain-free period re-quired for maximum efficacy depends on the weed spe-cies(97), the herbicide(97), the surfactant(16, 84), the herbi-cide formulation(23), the rate of application(25, 117), andenvironmental conditions(35). On the other hand, spray-ing should be done when the moisture status of the soilis adequate for vigorous growth. Furthermore, herbicideuptake is facilitated by succulence of the leaves(12, 93, 107,
112). In hot, dry weather, leaves have a waxier leaf cu-ticle not readily penetrable by herbicides.
Integrated treatmentsTypically, woody plant populations cannot be eliminatedby a single spray application. Most woody species havesufficient food reserves that allow them eventually tooutgrow the effects of a single herbicide spray applica-tion. Thus, repeated or integrated treatments that stressthe weeds over a longer period of time are usually re-quired for effective control, particularly for older, moreestablished infestations. For example, two herbicidesprayings a year apart virtually eliminated guava fromexperimental plots, whereas a single application resultedin the eventual recovery of the weed (44). Similar re-sults were reported for Rubus spp. (6, 7), gorse (13, 69),and lantana (40).
Likewise, burning or mechanical control methodsthat remove most of the plant biomass, followed by aherbicide application early in its recovery, also results
10
Herbicidal Weed Control Methods for Pastures and Natural Areas of Hawaii
in higher weed mortality than a herbicide spraying ofundisturbed plants(56, 69). Topping of woody plants reducestheir biomass, forces the plant to tap its food reserves tofuel regrowth, allows better herbicide coverage to beachieved, and provides more succulent leaves, whichare more readily penetrated by herbicides. This strategyhas been used effectively on lantana(26, 48), Rubusfruiticosis (no common name)(6), gorse(54), and onSolanum auriculatum (no common name) and turkeyberry, species closely related to apple-of-Sodom(100).Tropical soda apple (Solanum viarum) required a mow-ing followed by triclopyr applications for adequate con-trol(71).
In spraying previously treated plants, the succeed-ing treatment should not be done too early or too late.When the plant is in early flushing, translocation of car-bohydrates upward from the roots to the new flush willprevent the downward translocation of foliar-appliedherbicide. Applications should be made when a suffi-cient number of new leaves have fully expanded. Thisis when photosynthesis is active and translocation ofphotosynthate from the leaves is active as the injuredplant rebuilds its energy reserves. Waiting too long al-lows the weed to rebuild its energy reserves.
Climate can be exploited in chemical weed con-trol(53). In leeward areas subject to seasonal drought, her-bicides should be applied early in the rainy season. Atthis time, energy reserves in plants are low after beingtapped to support the new flush after the drought, leafarea is large, and leaves are succulent. After treatmentwith a selective herbicide, the plants would be defoli-ated during the wet growing season and would not beable to rebuild their energy reserves before the onset ofthe next dry season. In the meantime, growth of tolerantspecies would be unhindered by competition from theweedy plants, and soil moisture would be conserved. Inthe higher elevations with more uniform rainfall distri-bution, there is a surge in growth in the spring whentemperatures get warmer. This would be the best time toapply herbicides. However, brush in high-rainfall areastends to exhibit better recovery without the added stressof seasonal drought.
Kona rancher Allen Wall reported that slashingguava in the cool season and spraying the regrowth inearly summer (rainy season) before the weed can regainits vigor effectively controlled this weed of humid ar-eas. This strategy integrates climate with mechanical andchemical control methods.
Drift preventionHerbicides that drift from the target area do not contrib-
ute to weed control. More seriously, such herbicides cancause severe damage to nearby crops or other valuableplants. It is the legal responsibility of the applier to pre-vent herbicide drift. There are six principal factors thatincrease the risk of herbicide drift.
1. Proximity to sensitive plants. The first precau-tion in applying herbicides is to be aware of the locationof sensitive and valued non-target plants. The appliercan then make adjustments in the weed control programto avoid drift hazards too close to non-target plants.
2. Droplet size. Fine droplets have a greater poten-tial to drift than large droplets. High pressure spray andsmall nozzle orifices yield a greater proportion of “fines”than low pressure and large orifices. However, coarsesprays require higher spray volumes than fine spraysfor adequate coverage. The applier therefore must ad-just the spray to fit the conditions.
3. Wind. Herbicides should be applied during stilltimes of day. High winds will displace herbicides. Justhow great a wind velocity can be tolerated depends onthe other factors stated here, but in any case it shouldnot exceed 10 mph, or any wind speed limit stated onthe label.
4. Height of spray. The higher the arc of the spraythe greater the distance spray can drift. Thus, aimingthe spray up toward the canopy of tall brush increasesthe drift potential, particularly when high pressure (finemist) and volatile formulations (esters) are used.
5. Formulation. Long distance drift involves herbi-cide vapor. Ester formulations of herbicides are some-what volatile. Because of the threat of vapor drift, cur-rent ester formulations are manufactured in “low-vola-tile” formulations. However, even these can pose a threatif mismanaged. For example, applying even “low vola-tile” esters with a mist blower would greatly increasevolatilization into the air.
6. Timely weed control. One of the most effectivemeans to prevent drift is to take care of weed problemsearly. Most drift problems occur when treating tall brush.By tackling weeds while they are small, the applier cankeep the nozzles close to the ground, and thus avert theneed to spray upward into the air and the need to usehigh pressure to increase the reach of the sprayer. Also,lower herbicide rates are needed when the weeds aresmall.
Calibration of spray volume rateand herbicide concentrationTo ensure application of the recommended rate of a her-bicide, the applier must determine the spray-volume rate(SVR), i.e., the total amount of material (herbicide plus
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carrier) to be applied per acre (even if less than an acrewill actually be sprayed) because the herbicide rate de-pends on the SVR. To accomplish this, the applier mustcalibrate the sprayer. The simplest calibration procedureis to spray a plot of known area to determine the re-quired volume of water that will provide good cover-age, spraying at a constant, comfortable speed and low(15–45 psi), constant pressure. Thus SVR =
water sprayed (gal) 43560 sq ft
swath width (ft) x distance (ft) acre
Then, herbicide concentration =
recommended herbicide rate
SVR
Example 1. Boom sprayerCheck each nozzle by collecting the output over a set timeand measure the volume. The output of the nozzles shouldnot vary from one another by more than 10 percent.
Assume a boom sprayer with a 20-ft spray width.At a constant speed of 3 miles per hour, the sprayer dis-charges 4.2 gal of water over 300 ft. Thus,
For each acre to be sprayed, the recommended amountof herbicide must be diluted with enough water to makea total of 30 gal spray mixture. Assuming 0.5 gal herbi-cide/acre is recommended, then
herbicide concentration =
0.5 gal herbicide/acre
30 gal spray/acre
Thus the concentration of herbicide required is 1.7%.With this information, any volume of spray mixture canbe prepared.
Example 2. Power sprayer, orchard gun method1. Measure off a known area.2. Record the water level in the sprayer tank.3. Spray the known area uniformly with water as would
be done with the herbicide mix using a low, constantpressure and the same nozzle setting as will be usedin the application. The larger the area sprayed, themore accurate the calibration.
4. Determine the amount of water used by reading the
volume gauge and subtracting that volume from thestarting level.
Assuming a known area of 60 x 200 ft and that wateruse was 22 gal, then
Assuming a recommendation of 0.5 gal herbicide/acre:
herbicide concentration =
0.5 gal
80 gal
Thus the herbicide dilution required is 0.6%.
Example 3: Knapsack sprayer(BASF no-math version [unpublished handout])1. Mark off a calibration plot that is 18.5 ft by 18.5 ft.2. Spray water over the plot and measure the time in
seconds to do it: (example: time = 45 sec).3. At the same constant pressure, by regulator or con-
stant pressure on the handle, spray into a bucket forthe same time and then measure the volume of watercollected in fluid ounces: (example:volume collected= 25 fl oz). The number of fluid ounces collected isequal to the SVR in gal/acre (example: 25 gal/acre).
Assume that the herbicide label recommends 1 qt (0.25gal/acre); then, the concentration of herbicide should be:
0.25 gal/acre
25 gal/acre
Thus the herbicide dilution needed is 1.0%.
Important note: If the spray volume rate turns out to betoo high, repeat the calibration and try to get the sprayvolume rate lower. This can be accomplished by increas-ing the speed of application, reducing the sprayer pres-sure, using nozzles with a smaller orifice, or a combina-tion of these. Boom sprayer volume rates should be about25 gal/acre, orchard gun sprayers 30–80 gal/acre, andknapsack sprayers 20–40 gal/acre, depending on the sizeof the target weeds.
x
SVR =30 gal
acrex
4.2 gal
20 ft x 300 ft
43,560 sq ft
acre=
= 0.017, or 1.7%
SVR =80 gal
acrex
22 gal
60 ft x 200 ft
43,560 sq ft
acre=
= 0.006, or 0.6%
= 0.01, or 1%
12
Herbicidal Weed Control Methods for Pastures and Natural Areas of Hawaii
Drizzle foliar application
Logistics limit conventional sprayingThe greatest cost component in herbicide applicationsis labor, in part because of the large volume of carrier,usually water, that must loaded, transported, mixed, andsprayed. This is particularly difficult in areas that areremote from water sources or only accessible by foot,i.e., areas that must be treated with knapsack sprayers.In addition, conventional spraying is also laborious be-cause knapsack sprayers have short throws, so the ap-plicator must walk up to each weed treated, and becauseof the frequency of re-loading that is necessary. Becauseof this cost and the effort required in conventional spray-ing, weed control operations may not be performed in atimely manner. This allows weeds to grow larger be-tween treatments and become more difficult to control.On the other hand, a highly efficient method fosterstimely weed control and eventually requires less laborand material as weed size and stand density are reduced.The inefficiencies of treating severe weed infestationsare thus avoided.
The drizzle methodA cost- and labor-efficient method of herbicide applica-tion was developed by Shigeo Uyeda (now retired) forthe McBryde Sugar Company, Kauai. Originally calledthe “Magic Wand” method(76), the drizzle method em-ploys an orifice disk (Spraying Systems orifice plate4916-20, 0.020 inch diameter orifice recommended) inplace of an atomizing nozzle and a fine strainer (100–200 mesh) to keep the orifice clear. A fine jet-stream isejected (30 psi suggested pressure) through the orifice(Figure 2a, 2b), which breaks up into large droplets thatdrizzles onto the plants (Figure 2c). The large, sparselydistributed droplets are contrary to the widely acceptedconcept of an optimal droplet deposition pattern, i.e.,very many, very fine droplets(19, 67). Nevertheless, thedrizzle method has proved sufficiently effective and veryefficient(73, 75, 76, 77, 79, 80). Broadcast application is achievedby waving the wand over the target area. Precise spotapplication is achieved by aiming the wand at the targetweed. The drizzle apparatus can also be used in very-low-volume basal bark applications (see Basal barkmethod, below).
Figure 2a. The drizzle method of foliar herbicide application.
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Figure 2c. Droplet distribution of herbicide applied by the drizzle method.
Figure 2b. Close-up of drizzle apparatus nozzle.
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Herbicidal Weed Control Methods for Pastures and Natural Areas of Hawaii
Efficiency of the drizzle methodThe drizzle method is very labor-efficient. The effi-ciency of the method is derived from its very-low-vol-ume (VLV) application rate (1.6 gal/acre) and a throwof 15 ft. Only small quantities of water have to be loaded,transported, mixed with herbicide, and applied. Down-time is greatly reduced, as relatively few re-loadingsare required. The reach of the drizzle applicator meansthe applier does not have to walk up to each weed aswith conventional knapsack spraying. In open pastures,the user walking at 1 ft/sec and waving the wand in ahorizontal arc to cover a swath 20 ft wide can broad-cast-treat 1 acre in 36 minutes at the application vol-ume rate of 1.6 gal/acre. On trails, the applier with aconventional knapsack sprayer must treat each side ofthe trail in turn. The drizzle applier can treat both sidesof the trail in one pass. A trail 7 ft wide can be treated at2 mph. On Koaie Trail on Kauai, where clearing 3 milesof trail would have been required 576 worker-hours formanual clearing or 40 worker-hours for conventionalspraying, only 4.5 worker hours were required usingthe drizzle method,(75, 79) and weed suppression was ex-cellent. The greater manpower requirement of conven-tional spraying results from the higher volume rate thatwould have required more porters to carry water. Thiswould be exacerbated on trails with few or no watersources. Koaie Trail frequently descended to KoaieStream. The disparity in cost between conventionalspraying and drizzle application would have been evengreater where water must be transported over the entiretrail, expecially where the trail is rough and steep. Theexperience of Koaie Trail has been repeated on severalother trails on Kauai where mechanical control meth-ods have been replaced by drizzle applications of her-bicides and labor requirements have been reduced by83–98%(73, 75).
Other advantagesIn addition to labor efficiency, the drizzle method offersseveral other advantages:• Low drift potential—because of the large droplets,
drift is minimal.• Safety—heavy loads are a risk factor in injuries. Fur-
thermore, that risk is compounded by fatigue causedby carrying such heavy loads. This is especially so inrough and steep terrain. Very-low-volume methodsreduce the weight and number of loads that appliersand porters must carry. The applier can cover morethan an acre with a half-full knapsack.
• Reliability—unlike other more complex very-low-volume equipment, the drizzle method is not subject
to breakdowns because it employs ordinary sprayers.• Cost and convenience—any ordinary knapsack
sprayer can be easily and cheaply converted into adrizzle unit and back again. In addition, tank pres-sure is easier to maintain with a manual knapsacksprayer in a drizzle mode because of the very lowoutput. The drizzle unit is easily deployed, in con-trast to heavy power sprayers or crews of laborers formechanical control. One person on a moment’s no-tice can go off to treat a large area. The convenienceof the drizzle method encourages more timely weedcontrol. The resulting lower weed biomass makessucceeding operations easier and with less herbiciderequired.
• Versatility—the wand of the drizzle unit can be wavedto broadcast herbicides, aimed for a very precise spotapplication and, with a crop oil carrier (see below),used for basal bark treatments. With its reach of 15 ft,it can be used on brambles, weeds to 12 ft tall, andplants over the edge of cliff-side trails.
• Affordability of oil carriers—because of the very lowvolume of the drizzle method, crop oil carriers areaffordable: only 1.3 gal/acre or less is required inbroadcast applications. Ester formulations of triclopyrcan be applied in a crop oil carrier to treat weeds tol-erant of foliar applications of triclopyr in water, suchas Mauritius hemp and gorse. Triclopyr in crop oilcan also be used in very-low-volume basal bark orstump treatments of susceptible woody species (SeeBasal bark method, below).
Limitations of the drizzle methodFor certain weeds, the drizzle method is not as effectiveas conventional spraying. In addition, the user is lim-ited to liquid herbicides (solutions or emulsions) withlabels that allow a high enough concentration to applyan effective amount at a very low spray-volume rate.Wettable powders will clog the strainer or the fine ori-fice of the disk. There are only a handful of herbicidesthat are appropriate for drizzle application (Table 1).
CalibrationAs in any method of application, calibration is criticalto delivering the correct volume and, thereby, the de-sired herbicide rate. This ensures efficiency, efficacy,economy, and environmental protection. The most con-venient set-up is to use an orifice disk with a 0.02 inchorifice at a tank pressure of 30 psi. With a manual knap-sack sprayer lacking a pressure regulator, constant pres-sure can be achieved by maintaining constant pressureon the handle. This will be easy to do because the out-
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put is so low that the tank pressure declines very slowly.It really does not matter what pressure is used as long asit is not so high as to atomize the output nor too low tomaintain maximum throw. Of course, constant pressureshould be maintained not only during calibration but alsoduring the actual application. (To observe the dropletdistribution pattern, drizzle a dry paved area, walking at1 ft per second and covering a swath 20 ft wide). Thecalibration method described here assumes a spray swathof 20 ft, an application speed of 1 ft/sec, and an SVR of1.6 gal/acre. Application speed can then be adjusted fornarrower swaths, e.g., increasing the speed three-foldfor spray swaths of one-third the original calibrated spraywidth (20 ft). However, to treat very narrow swaths, e.g.,a 2-ft swath along a fence line, increasing applicationspeed sufficiently will not be practical, so a smaller ori-fice disk must be used to provide a lower output andsmaller droplets, or the herbicide concentration must bediluted and the SVR increased to obtain the desired her-bicide rate.
To calibrate a drizzle unit:1. Measure the water output of the drizzle sprayer by
collecting the discharge for 1 minute at constant pres-sure. (Because of the low volume, the collected wa-
ter is best measured in milliliters (ml) with a metricgraduated cylinder, or the collection period can beincreased to several minutes until a volume measur-able in a metric measuring cup is collected):
Volume collected (ml/min)
60 sec/min
2. Divide output by 3785 (ml/gal) to convert output togal/sec:
Output (ml/sec)
3785 ml/gal
3. A swath 20 ft wide and 2178 ft long covers one acre.At a walking speed of 1 ft/sec, it would take 2178 secto treat 1 acre.
43560 sq ft/acre
20 sq ft/sec
4. Multiply (2) by (3) to get the spray volume rate ingal/acre:
Output (gal/sec) x 2178 sec/acre = SVR (gal/acre)
Table 1. Herbicides for drizzle application.(Always check labels before use, as they are subject to revision).
Method Concentration4
Product Herbicide Site1 Use2 of application3 (%)
Banvel® dicamba P, F, N B f 15
Garlon® 3A triclopyr amine P, F, N B f 20
Garlon® 4 triclopyr ester P, F, N B f, bb 20
Hi-Dep® 2,4-D amine*5 P, F, N B f 15
MCP Amine® MCPA P, F, N B f 15
Pathfinder® II triclopyr ester P, F, N B bb 100
Redeem® triclopyr amine P B f 20
Remedy® triclopyr ester P B f, bb 15
Rodeo® glyphosate5 A, N NS f 15
Roundup® glyphosate5 P, F, N NS f 20
Velpar® L hexazinone P, F, N NS f, s 67
*Restricted.1A = aquatic, P = pasture, F = forest, N = noncropland. Check label for specific uses.2B = broadleaves or dicots, NS = nonselective.3f = Foliar, bb = basal bark, s = soil.4Suggested concentration based on 1.6 gpa application volume rate. If allowed, higher concentrations may be used. Otherwise, higherherbicide rate requires higher application volume rate, e.g., 3.0 gal/acre or higher. Lower concentrations are sufficient for more susceptiblespecies and for seedlings.5Many brands of 2,4-D and glyphosate are available. Check label for site uses and allowed concentrations. 2,4-D sold in quantities of a quartor less is not restricted.
= Output (ml/sec)
= 2178 sec/acre
= Output (gal/sec)
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Herbicidal Weed Control Methods for Pastures and Natural Areas of Hawaii
Alternatively, the equations above can be summarizedto calculate the SVR for applicaations 20 ft wide and anapplication speed of 1 ft/sec:
Output (ml/min) x 0.0096 = SVR (gal/acre)
5. Determine the concentration of herbicide by dividingthe recommended herbicide rate by (4), the SVR:
0.25 gal herbicide/acre (example rate)
1.5 gal/acre (example SVR)
6. Determine the speed to treat narrower swaths, suchas a trail, from Step 4. Treating a narrower swath thanthe 20-ft one calculated in Steps 1–4, for example, 7ft, requires a greater application speed to maintainthe same SVR:
20 ft
7 ft
Drizzle foliar application, water carrierHerbicides soluble or miscible in water can be drizzledover weeds at the appropriate concentration. In broad-cast applications, the wand should be aimed over thetarget plants and waved to achieve uniform distribution.The wand can be waved in a circular motion or loopedin mid-swing to avoid underdosing the middle and over-dosing the edges of the swath as the wand slows at theends of the swing before its direction is reversed. Thebasic principles of herbicide application apply to drizzleapplication as they do to conventional spray applica-tions. There should be uniform distribution of the drop-lets over the whole canopy of the target weed withoutoverdosing. Taller weeds are a problem because the leeside of the plant would be underdosed. These can betreated from two opposite sides to ensure complete cov-erage. However, it would probably be more economicalinstead to re-treat in a few months when there is a newflush of growth and with the canopy thinned out by theprevious treatment. After the standing weed populationhas been eliminated, reinfestations should be re-treatedwhen the weeds are small, semi-annually or annuallydepending on the climate. At this time the weeds will bemore susceptible and lower herbicide rates can be used.Thus over time the amount of herbicide required willdiminish. For example, in annual applications on KoaieTrail on Kauai, the second application required only 41percent as much herbicide as the first application, 39percent on the third, and 25 percent on the fourth(75).
Weed species susceptible to drizzle-applied triclopyrinclude highbush blackberry, yellow Himalayan rasp-berry, catsclaw, Formosan koa, bur bush, sacramento bur,melastoma, Indian pluchea, and sourbush. Weeds sus-ceptible to glyphosate are lantana, guineagrass, Jobstears, Californiagrass, palmgrass, fountaingrass, andhuehue haole.
Drizzle foliar application, crop oil carrierCertain weeds that are tolerant of herbicides in watercarrier may succumb to herbicides in an oil carrier. Non-phytotoxic crop oil can be used as a carrier with the esterformulation of triclopyr. The oil, which contains emulsi-fiers to make mixing with water possible, is harmless toplants but helps oil-soluble herbicides penetrate leavesand stems and thereby increases efficacy. Crop oil mayalso be used as an adjuvant at 0.5–20%. When using oilas an adjuvant, the herbicide and oil should be mixedfirst, then added to water and made to volume with morewater. Gorse and Mauritius hemp are examples of weedstolerant of applications of triclopyr ester in water butsusceptible to the same herbicide in a crop oil carrier.
Cut-surface methods
NotchingA very effective albeit labor-intensive way to chemi-cally control brush and trees is to mechanically penetratethe bark and place the herbicide directly into the sap-wood (xylem) of the plant (Figure 3). The herbicide isthen translocated throughout the plant, provided that thetarget plant has actively functioning leaves. Specializedequipment such as tree injectors may be used to piercethe bark and deposit the herbicide. However, a simplemethod requiring no specialized equipment is the “notch-ing” or “hack and squirt” method. In this method, notchesan inch or so deep into the sapwood are made every 4inches around the trunk with an ax or machete. Becauseherbicides do not move radially (horizontally) in the plantvery well, the herbicide must be placed in wounds madeat intervals around the circumference of the trunk. Her-bicides applied to a single notch will translocate verti-cally and likely kill only that vertical segment of theplant. The wound is cut at a 45° angle to form a recep-tacle to retain the herbicide, and the bark is pried awayfrom the trunk to increase the area of herbicide contactwith the sapwood. The notches should be made as closeto the ground as possible to enhance suppression of budsat the root crown,(58, 61) although this is not necessarywith all species(96). A study done in Australia demon-strated that herbicide applications to wounds made by
= 0.17, or 17%
1 ft/sec x = 2.86 ft/sec, or 3 ft/sec
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puncturing the trunk with a narrow bladed instrumentgave better kill than did slashing it with a machete(95).This was attributed to better penetration into the sap-wood by the narrow blade. Although the machete causeda longer cut, only a short section of the blade actuallyreached deep into the sapwood. Also, the narrow-bladewound probably retained more herbicide. Herbicidestended to run out of the edges of machete cuts. In treesthat fork close to the ground, it would also be a goodidea to notch each branch on the inside of the crotch toimprove distribution of the herbicide within the aerialportion of the tree.
Notching is very effective on dicot species that haveone or a few trunks, provided a suitable herbicide is avail-able. Obviously, this method would be difficult on shrubswith many fine stems. Trees of 8-inch trunk diametercan be treated at a rate of 21 per worker-hour(82, 83). Be-cause each plant is treated individually, there is littlelikelihood of injury to non-target plants.
For species somewhat tolerant of the herbicide used,notches can be made end-to-end in a continuous ringaround the trunk (frilling)(61, 87). This in effect doublesthe applied dose(95). For larger trees, drilling holes intothe trunk allows a higher dose to be applied (Figure 4a,4b). For example, spaced notches treated with dicambaor glyphosate were inadequate to kill large roseappletrees. However, excellent control was obtained with thesame herbicides when 4 ml of either was applied to
drilled holes, 0.5 inch in diameter by 3–4 inches deep.The holes were drilled at a downward angle every 10inches around the base of the trunk(43, 44).
The best herbicide to use in notching depends onthe weed to be treated. Any of the brush-killers could beappropriate. The salt formulations are preferable to theesters because they are translocated more readily, al-though the latter are usually satisfactory(49, 61, 95). In addi-tion to the brushkillers, glyphosate is very effective onseveral species (e.g., fayatree, karakanut, paperbark, androseapple) when applied by the notching method or todrilled holes.
The amount of herbicide that should be applied var-ies with weed species. The recommended rate is usually1 ml per notch or 4 ml per drilled hole of the concen-trated herbicide or of herbicide diluted as much as 20times. At 1 ml of concentrated herbicide per notch, 1 floz of herbicide is sufficient to treat 28 notches. There isno particular advantage to diluting the herbicide, exceptfor economy in those cases where the diluted herbicide ispotent enough to kill the plant. The notches can hold onlya limited volume of herbicide; some of it will leak outfrom the edges of the notch. More concentrated solutionsallow more herbicide to be absorbed into the xylem. How-ever, some herbicide labels dictate the concentrations thatmay be used. Should the label require dilution, mix onlyenough for one day’s needs, because dilution with waterwill accelerate degradation of the herbicide.
Figure 3. Cut-surface (notching) herbicide application. Notches must be made around the stem.
18
Herbicidal Weed Control Methods for Pastures and Natural Areas of Hawaii
Cut-stump methodA variant of the cut-surface treatment, the cut-stumpmethod, is useful in dry areas where there is a need toclear standing vegetation. The plant is cut down andconcentrated herbicide is immediately applied to thesapwood of the stump (Figure 5). It is essential that the
Figure 4b. Applying herbicide into drilled holes.Apply 3–4 ml of herbicide concentrate to each hole, unless otherwise directed by the label.
Figure 4a. Drilling holes to treat a large tree.Holes about 5⁄8 inch diameter by 31⁄2 inches deep must be made at downward angle at12-inch intervals around the trunk.
application be made immediately after cutting, becausethe sap in the sapwood will recede into the stump, draw-ing down the herbicide with it into the region of the rootcrown where shoots originate. Waiting even a few min-utes allows air into the sapwood and blocks the entry ofthe herbicide, much as a vapor lock in a fuel line blocks
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the flow of fuel(49). This method may not work in high-rainfall periods because the sap will ooze out of the stumpand keep the herbicide from entering the sapwood(44).
Basal bark methodThe basal bark method is very effective for killing largeshrubs and small trees(28, 58). However, like notching, it islabor-intensive because each plant must be individuallytreated. The high-priced oil carrier also adds to the ex-pense. This combined high cost of material and laborrestricts the utility of the basal bark method to small popu-lations of hard-to-control species or other special situa-tions requiring sure “kill” or protection of nearby non-target plants that would be injured by foliar spray drift.
In the basal bark method, an oil-soluble formula-tion of a suitable herbicide and a light oil are used topenetrate the bark. This solution, 2–8% herbicide in oil,is sprayed or brushed onto the base of the trunk of thetarget plant. The trunk is wetted from about the 20-inchlevel down to the soil line (Figure 6). Effective controlrequires that the entire circumference of the trunk betreated. Misses along the trunk circumference could al-low buds to sprout(36). There should be a little runoff towet the soil around the base of the trunk to ensure thatthe root crown, which is an active zone of bud forma-
tion, is adequately treated. Plants susceptible to basalbark treatments would be even more susceptible to stumpbark treatments with the same oil-herbicide treatment(Figure 7).
The oil used as the carrier should be a light oil suchas diesel, kerosene, or a crop oil made specifically forthis purpose, which is capable of penetrating the essen-tially waterproof bark. Heavy oils such as motor oil orgear oil are not as effective in penetrating the bark, anduse of used motor oil would be illegal. Crop oil, a highlyrefined oil, is less toxic than fuel oils and is nearly odor-less. For basal bark treatments, water is useless as a car-rier because it cannot penetrate the bark.
The herbicides used in basal bark treatments must beoil soluble, either esters or long-chain amine salts.Triclopyr, 2,4-D, and related herbicides are available inester formulations and are thus registered for basal barktreatments, along with some salts, such as imazapyr, thatcan be mixed with oils. Although the effectiveness of 2,4-D against woody plants is limited, there are a few speciesagainst which 2,4-D in basal bark treatments is useful.However, it is very effective on stumps of many species,even though it may not be effective on standing trees ofthe same species. For non-crop and forest uses, imazapyrin oil is an effective basal bark and stump treatment.
Figure 5. Herbicide application to cut-stump surface.Application of herbicide concentrate should be made immediately after felling. Worksbest in dry season.
20
Herbicidal Weed Control Methods for Pastures and Natural Areas of Hawaii
Very-low-volume basal-bark and stumpapplicationsEster formulations of triclopyr may be mixed in oil at20% or more and applied as thin-line or very-low-vol-ume applications to control woody plants (Figure 8) andto kill stumps (Figure 9). Triclopyr ester may also beused as the concentrate in this way. Low-output equip-ment must be used to avoid overdosing. On larger plants,applications should be made at least on two oppositesides of the basal stem. Susceptible species are youngplants with juvenile bark and those species with thin bark,such as strawberry guava, Molluca albizia, gorse,catsclaw, and velvet tree. Downy rosemyrtle, Formosankoa, and melastoma are also susceptible but require ap-plications from two sides. Large trees and species withthick, corky barks cannot be controlled by this method(e.g., paperbark, java plum). Applications to stumps or toresprouting stumps should be very effective (Figure 9).
Figure 7. Stump-bark herbicide application.Apply herbicide-oil solution to the bark completely around thestump. This is usually the most effective method to kill woodyplants.
Figure 6. Basal bark herbicide application.Apply herbicide-oil solution completely around the stump fromground level to 18–24 inches.
Soil-applied herbicidesSome pre- and postemergence herbicides are applied tothe soil and taken up through the roots of target plants.Three granular or pelleted herbicides are registered foruse in Hawaii: dicamba (Veteran® 10-G [BASF]), hex-azinone (Velpar® and Pronone Power Pellets® [DuPont]),and tebuthiuron (Spike® 20P [Dow Agrosciences]).Dicamba and tebuthiuron selectively control broadleafweeds. Hexazinone, also available as a wettable powderand a liquid concentrate, is nonselective but may be ap-plied selectively in spots at the base of plants or in gridpatterns (hot spots) in larger infestations. While grassesare killed at the small application spots, no major dam-age to the grass sward is incurred. The roots of broadleavesthat feed where the hexazinone hot spots are will absorbthe material, which then kills them.
Because of its low animal toxicity and poor mobil-ity in soils, tebuthiuron is an environmentally safe her-
21
UH–CTAHR
Figure 8. Very-low-volume basal bark herbicide application.Apply oil-herbicide solution in horizontal or vertical streaks. Works best on thin-barked species and plantswith juvenile bark.
Figure 9. Very-low-volume herbicide application to stump bark.Apply oil-herbicide solution in streaks around the stump bark.
22
Herbicidal Weed Control Methods for Pastures and Natural Areas of Hawaii
bicide. It is active against guava, koa haole, apple-of-sodom, and christmasberry, although larger plants maybe more tolerant(47, 74). Control of fayatree, Formosan koa,gorse(46, 48), and downy rosemyrtle with tebuthiuron(Univ. Hawaii, unpublished data) has been poor. It isimportant to apply the proper amount of any granularherbicide. The material is expensive, and grass can beinjured by an overdose. Note that with Spike 20P(tebuthiuron), 10 lb/acre is equivalent to only 2 pelletsper square foot.
Dicamba, an excellent foliar herbicide on poly-gonaceous weeds (spiney emex, kamole) and on guava
and other species, has not shown much promise onHawaii’s woody plants in the granular formulation(45, 46).
Hexazinone is a persistent and mobile herbicide thatis of low animal toxicity. It would pose no groundwatercontamination threat when used sparingly, particularlyin drier areas. Because it is nonselective, it should notbe used in broadcast applications over large areas in anycase. Although hexazinone is very effective on mostweeds, the efficacy of it and tebuthiuron have been er-ratic against weeds in small-plot soil applications in for-ests (Univ. Hawaii, unpublished data).
23
UH–CTAHR
This appendix lists and describes some of the herbicidesregistered for weed control in pastures and ranges inHawaii. The primary source of the information on her-bicide properties is the Herbicide Handbook of the WeedScience Society of America, 7th edition(113, 114) and thelist of registered herbicides provided by the PesticidesBranch of the Hawaii Department of Agriculture. Inaddition, some information was obtained from labels andtechnical sheets issued by the manufacturers. Becauseof constant changes in registration and labels, the useris responsible for verifying that the information in thispublication is current.
Explanation of herbicide description
Use“Use” refers to situations and types of weed infestationswhere the herbicide may be useful. “Selectivity” refersto the capability of the herbicide to kill one type of plant,usually the weed, but not another. “Preemergence”means before the newly planted desirable plants or weedsor both emerge from the ground; “postemergence” meansafter these plants are up. Some herbicides may be effec-tive both preemergence and postemergence.
FormulationsHerbicides are of several different types of formulations.Herbicide manufacturers and formulators design theseformulations based on chemical properties, intended use,and customer demands. Some of these formulations are:
Water soluble solids. These powders or crystals canbe dissolved in water for application. The mixture is atrue solution; the solutions are clear.
Water soluble concentrates. These liquid concen-trates, usually salt formulations, can also be dissolvedin water to form true solutions.
Emulsifiable concentrates (EC). These are oil-soluble products that are formulated with emulsifiers sothey can be diluted with water. The resulting emulsionsare not true solutions. The oily herbicide is dispersed asmicro-droplets in the water carrier, forming a milkyemulsion. The emulsion will begin to separate into itswater and oil components if allowed to stand withoutoccasional agitation. Emulsifiable concentrates can be
Appendix 1Herbicides Registered for Use in Pastures
and Natural Areas of Hawaii
dissolved in oil for basal bark applications or to enhancefoliar uptake, if allowed by the label. Herbicides in ECformulations are slightly volatile. They may vaporizefrom spray droplets and plant and soil surfaces, espe-cially in hot weather, and they may injure non-targetplants downwind. However, current formulations are“low-volatile” which means the tendency to volatilizeis greatly reduced compared to the old ester formula-tions. Still, greater precautions must be taken with es-ters than with non-volatile formulations.
Wettable powders. Wettable powders are mixturesof insoluble herbicides in clay and surfactants that canbe mixed with water to form a suspension (solids sus-pended in water). The suspension requires constant agi-tation to prevent settling. For this reason, wettable pow-ders must not be used without an agitator in the tank.Similar formulations are the flowables and dry flowables.The flowable is a pre-slurried form of the wettable pow-der designed for easier handling. The dry flowable ordispersable granule is designed for “dustless” handling.Both also require vigorous agitation during applicationto prevent settling. Wettable powders and its variantscontain 60–90% of the herbicide.
Granules/pellets. Granulated material, exceptdispersable granules, are designed for dry soil applica-tion. Such herbicides must be rather persistent andreadily absorbed by roots. They are applied by hand,mechanical spreaders, blowers, or aircraft. Granules andpellets for direct application to the soil are of low con-centration, 2–20%.
ProductsSome herbicides are manufactured or formulated by sev-eral firms; each has its own brand name. Others, stillprotected by patent, may have only a single manufac-turer but several brand names. Manufacturers may usevariants of a brand name on different formulations ofthe same herbicide and on mixtures in which the herbi-cide is used. For example, Tordon 22 K (DowAgroSciences) contains only picloram, but Tordon 101(Dow AgroSciences) is a mixture of 2,4-D and piclo-ram. The user should be aware of the content of the prod-uct when buying a herbicide. Different brands of thesame herbicide may have different registered uses. The
24
Herbicidal Weed Control Methods for Pastures and Natural Areas of Hawaii
applier cannot assume that different brands, even of thesame herbicide and formulation, can be used in the sameway.
ApplicationListed under this subheading are the approved applica-tion methods of the herbicides under discussion. Beaware that different brands of the same herbicide mayallow different application methods, so the labels of theherbicide being considered for use must be read.
Behavior in plantsPlants absorb herbicides via the foliage, the roots, orboth, depending on the characteristics of the chemical.Most herbicides are systemic, i.e., once absorbed by theplant, they must be translocated to some site where theyaffect the plant. Herbicides travel downward from theleaves to the roots via the phloem and upward from theroots via the xylem (called “sapwood” in woody plants).Some herbicides are restricted to one transport systemor the other, others are immobile, and still others travelmore or less freely in both systems. (Many herbicidesthat are phloem-mobile in foliar application can be ap-plied cut-surface into the xylem). This chemical charac-teristic also influences how herbicides are managed.
The mode of action of herbicides varies. Plant hor-mones cause rapid but abnormal growth, photosyntheticinhibitors shut down photosynthesis, contact herbicidesdisrupt cell membranes and cause plants to dry up, in-hibitors of cell growth and division cause stunting, in-hibitors of respiration cause the plant to use up its storedenergy, and inhibitors of biochemical synthesis causecollapse of the plant. The symptoms produced are cluesto whether the herbicide is working or not and whetherit is the cause of non-target plant injury.
Behavior in soilsTwo characteristics of herbicide behavior in soils areimportant in herbicide management: persistence andmobility. Mobility, in turn, depends on how tightly theherbicide is adsorbed by or adheres to soil particles. Aherbicide resistant to degradation (persistent) will beactive longer both in the soil and in plants. If it is alsomobile, it may cause problems by moving with waterout of the target area and injuring plants in non-targetareas or getting into the groundwater. A non-persistent,mobile herbicide, however, will degrade before it cantravel out of the target area or into groundwater. A per-sistent, immobile herbicide will stay in place until it iseventually degraded.
The “half-life” of a herbicide is the time required to
detoxify half of the herbicide present in an ecosystem;this is the standard measure of persistence. Degradationof pesticides is faster in warm, moist soils and slower incold, dry soils. In general, herbicide leaching is more ofa problem in high-rainfall areas than dry areas and insandy soils than in soils high in clay and organic mattercontent.
ToxicityPesticides must undergo rigid toxicity tests to determinetheir safety. Listed under this heading is the acute oralLD
50 of the herbicide for rats. Although only results on
rats are given, the testing protocol requires various testson fish, birds, dogs, and other animals to develop thetoxicology profile of the herbicide. “LD
50” refers to the
amount of material in mg per kg of bodyweight of thetest animal that is required to kill 50 percent of the samplepopulation. The toxicity rating scale is listed in Table 2,along with some example pesticides and common non-pesticidal products as a frame of reference (note that thehigher the LD
50, the lower the toxicity).
RegulationsPesticides are categorized into two groups for regula-tory purposes: “restricted use” and “unrestricted.” Ap-plication of restricted use chemicals requires that theapplier or the applier’s supervisor be certified to applyrestricted pesticides. The “restricted” category is as-signed to chemicals not only because of hazard to hu-mans and animals but also for potential hazard to non-target plants and contamination of the environment. Pi-cloram, for example, is restricted because of its hazardto non-target plants and to groundwater, but it is of verylow animal toxicity. Unrestricted chemicals may be pur-chased and used by persons without certification. Re-gardless of classification, however, any pesticide usemust be consistent with its label directions.
For a pesticide to be used legally in Hawaii, it mustbe licensed for sale and it must be registered for the in-tended use. Some pesticides and uses may be national;that is, they can be used in all states. Some pesticidesand uses may be restricted to one or more states. Regis-trations are specific for a single brand-name product.Thus a new brand of 2,4-D must be newly registered foruse and sale. Different brands or different formulationsof the same herbicide may have differences in the labelthat makes one method of application legal with oneproduct and illegal with another, even though the activeingredient is identical.
Grazing restrictions mandate how long animals mustbe kept off treated pastures or how many days before
25
UH–CTAHR
slaughter the animal must be removed from treated pas-tures. Grazing restrictions are more severe for lactatingdairy animals than for meat animals. The restrictionsare aimed at preventing herbicide residues from con-taminating milk and meat. Herbicides applied accord-ing to label directions do not represent a threat to ani-mal health.
Included in this listing are herbicides for pasturesand natural areas. For aquatic sites refer to Vandiver(109).Pesticides labels and regulations are frequently changed,so it is the responsibility of the user to read and heed thelabel to ensure compliance.
Table A-1. The rating scale of toxins and example substances.Each pesticide product is assigned a signal word to warn users of its toxicity. The signal words (printed on the label) and theirapproximate hazards are listed in Table 3.
Toxcity Oral LD50
rating Category (mg/kg bodyweight) Example (with LD50)
1 Extremely Toxic < 5 Parathion (2)
2 Very Toxic 5–49 Vitamin D (10), dinoseb (40)
3 Moderately Toxic 50–499 Nicotine (50), paraquat (150), caffeine (200)
4 Slightly Toxic 500–4999 2,4-D (700), aspirin (750), bleach (2000), triclopyr (2140),
table salt (3320)
5 Almost Non-toxic 5000–14,999 Glyphosate (5000), picloram (8200)
6 Non-toxic 15,000+
Table A-2. Pesticide toxicity signal words and approximatelethal dose.
Signal word Amount needed to kill a 150-lb human
DANGER 1 teaspoon or less
WARNING 1 teaspoon to 1 tablespoon
CAUTION 1 ounce to 1 pint
26
Herbicidal Weed Control Methods for Pastures and Natural Areas of Hawaii
Clo
pyr
alid
Tran
slin
e®, a
min
e sa
lt (D
ow A
groS
cien
ces)
Ap
plic
atio
nB
ehav
ior
in p
lan
tsB
ehav
ior
in s
oil
Toxi
city
Reg
ula
tio
ns
Use
Sel
ectiv
e po
stem
erge
nce
con-
tro
l o
f a
nn
ua
l a
nd
pe
ren
nia
lb
roa
dle
ave
s in
pa
stu
res
an
dna
tura
l are
as.
Esp
ecia
lly e
ffec-
tive
on
mo
st l
eg
um
es
an
dco
mpo
site
s, in
clud
ing
Mad
agas
-ca
r rag
wor
t (fir
ewee
d). E
ffect
ive
on P
roso
pis
spec
ies
in th
e U
.S.
Sou
thw
est.
Fol
iar
at 0
.5 lb
/acr
e(l.
3 pt
), a
t up
to 4
0ga
l/acr
e sp
ray-
volu
me-
rate
.
Rea
dily
abs
orbe
d by
fol
iage
an
d
roo
ts.
Tra
nsl
oca
tes
pri
ma
rily
in
th
e
ph
loe
m,
acc
um
ula
tin
g
in
gro
win
gp
oin
ts i
n s
tem
s a
nd
ro
ots
.H
orm
on
e t
ype
he
rbic
ide
.C
ause
s be
ndin
g an
d cu
rvin
g,sw
ellin
g of
ste
ms,
elo
ngat
ion,
leaf
cur
ling,
chl
oros
is.
Lo
w a
dso
rpiti
vity
, m
od
era
tele
ach
ing
. N
ot
vola
tile
o
rph
otod
egra
ded.
Deg
rada
tion
by m
icro
bes.
Hal
f-l i f
e 12
–70
days
in a
ran
ge o
f soi
ls.
Low
tox
icity
to
fish
and
bird
s. L
D50
for
rats
>50
00 m
g/kg
.
Unr
estr
icte
d.G
razi
ng
: L
ive
sto
ck f
rom
tre
ate
d a
rea
s sh
ou
ld b
egr
azed
for
sev
en d
ays
onun
trea
ted
past
ures
bef
ore
mo
vin
g o
nto
bro
ad
lea
fcr
op
s a
rea
s. L
ive
sto
ckd
rop
pin
gs
ma
y h
ave
enou
gh u
nalte
red
clop
yra-
lid to
inju
re b
road
leaf
cro
ps.
2,4-
DA
lthou
gh th
e fo
llow
ing
com
men
ts a
re s
peci
fic fo
r 2,
4-D
, rel
ated
phe
noxy
s M
CP
P a
nd 2
,4-D
P h
ave
sim
ilar
prop
ertie
s. M
CP
A is
list
ed s
epar
atel
y. T
hese
com
poun
ds a
re o
ften
used
in c
omm
erci
ally
form
ulat
ed m
ixtu
res.
Am
ine
salt
fo
rmu
lati
on
s:C
lean
Cro
p A
min
e® (
Pla
tte)
For
mul
a 40
® (
Rho
ne-P
oule
nc)
Hi D
ep B
road
leaf
Her
bici
de® (
PB
I Gor
don)
Sab
er® (
Pla
tte)
Sav
age®
(P
latte
)W
eeda
r 64
® (
Nuf
arm
)W
ibur
-Elli
s A
min
e 4®
(W
ilbur
-Elli
s)O
ther
sM
ixtu
res
Est
er f
orm
ula
tio
ns:
Cle
an C
rop
Low
Vol
4® (
Pla
tte)
Est
eron
6E
® (
Ver
tac)
Sal
vo® (
Pla
tte)
Wee
done
638
® (
Nuf
arm
)W
ilbur
-Elli
s Lo
Vol
-4® (
Wilb
ur-E
llis)
Oth
ers
Mix
ture
s
Con
trol
s m
any
herb
aceo
us a
ndso
me
wo
od
y b
roa
dle
ave
s in
pa
stu
res
an
d n
atu
ral
are
as.
Est
ab
lish
ed
g
rass
es
very
tole
rant
exc
ept
for
som
e la
wn
spe
cie
s. S
en
siti
ve s
pe
cie
s:gu
ava,
joe
e, M
adag
asca
r ra
g-w
ort
, m
orn
ing
glo
ry,
tro
pic
ager
atum
.
Fo
liar
spra
y, b
asa
lb
ark
(e
ste
rs o
nly
),an
d cu
t-su
rfac
e (i
n-je
ctio
n, n
otch
ing,
cut
-st
ump)
.
A
po
ste
me
rge
nce
fo
lia
rh
erb
icid
e,
2,4
-D i
s tr
an
slo
-ca
ted
prim
arily
in th
e ph
loem
,ac
cum
ulat
ing
in t
he g
row
ing
poin
ts o
f ste
ms
and
root
s. It
sef
fect
is
horm
onal
; it
caus
esra
pid
but
abno
rmal
gro
wth
.T
he
ste
ms
an
d l
ea
ves
of
trea
ted
plan
ts c
urve
ext
rem
ely
and
leav
es b
ecom
e ch
loro
ticbe
fore
dea
th o
f the
pla
nt.
App
lied
at c
onve
ntio
nal r
ates
,2
,4-D
to
xici
ty
to
pla
nts
dis
sip
ate
s in
l–
4 w
ee
ks i
nw
arm
, m
oist
soi
ls.
Alth
ough
som
ew
ha
t m
ob
ile i
n s
oils
,re
ad
y d
eg
rad
atio
n p
reve
nts
leac
hing
bey
ond
6 in
ches
.
Low
ord
er o
f tox
icity
.A
cute
ora
l LD
50 f
orra
ts is
300
–100
0 m
g/kg
. C
hron
ic t
oxic
ity:
2 ye
ars
feed
ing
tria
lso
n r
ats
an
d d
og
spr
oduc
ed n
o ef
fect
.R
eadi
ly e
xcre
ted
byan
imal
s.
Re
stri
cte
d,
dri
ft h
aza
rd,
exce
pt fo
r qua
ntiti
es o
f one
quar
t or l
ess,
rega
rdle
ss o
fco
ncen
trat
ion
and
num
ber
of u
nits
pur
chas
ed o
r use
d.G
razi
ng:
for
lact
atin
g an
i-m
als
on p
astu
res
trea
ted
with
up
to 2
lb/a
cre,
7 d
ays
wit
hh
old
ing
. F
or
me
at
an
ima
ls,
no
with
ho
ldin
g,
but
rem
ove
anim
als
from
past
ures
tre
ated
with
2 lb
/a
cre
3
d
ays
b
ef o
resl
augh
ter.
Ap
plic
atio
nB
ehav
ior
in p
lan
tsB
ehav
ior
in s
oil
Toxi
city
Reg
ula
tio
ns
Use
27
UH–CTAHR
Flu
azif
op
-p-b
uty
lF
usila
de D
X® o
r F
usila
de II
®
Ap
plic
atio
nB
ehav
ior
in p
lan
tsB
ehav
ior
in s
oil
Toxi
city
Reg
ula
tio
ns
Use
Sel
ectiv
e an
nual
and
per
enni
algr
ass
cont
rol i
n no
n-fo
od a
reas
.N
o a
ctiv
ity
on
dic
ots
. G
rass
grow
th r
etar
dant
at l
ow r
ates
.
Pos
tem
erge
nce
folia
rap
plic
atio
n at
0.2
5–0.
375
lb a
ctiv
e/ac
re,
1–1.
5 pt
/acr
e. A
pply
with
cro
p oi
l adj
uvan
t.
Rap
idly
abs
orbe
d, r
ainf
ast
in2
hr.
Tra
nslo
cate
s sl
owly
in
ph
loe
m
tow
ard
s g
row
ing
poin
ts.
Cut
s of
f sy
nthe
sis
offa
tty
aci
ds
an
d t
hu
s m
em
-br
anes
in g
rass
es.
Low
ads
orpt
ivity
but
ave
rage
half-
life
in s
oils
15
days
so
low
risk
of g
roun
dwat
er c
onta
mi-
natio
n.
LD50
in ra
ts 4
096
mg/
kg, l
ow to
xici
ty.
Unr
estr
icte
d.D
o no
t gra
ze tr
eate
d ar
eas.
Do
not a
pply
thro
ugh
irrig
a-tio
n sy
stem
s.
Gly
ph
osa
teR
ound
up O
rigin
al®, R
ound
up P
ro®, R
ound
up U
ltra®
; Rod
eo® fo
r aq
uatic
and
upl
and
site
s (M
onsa
nto)
Sev
eral
new
pro
duct
s by
Mon
sant
o an
d ot
her
com
pani
es n
ow a
vaila
ble.
Non
sele
ctiv
e bu
t esp
ecia
lly e
ffec-
tive
agai
nst g
rass
es in
pas
ture
s,na
tura
l are
as, a
quat
ic s
ites.
Con
-tr
ols
sedg
es,
herb
s, e
mer
ged
aqua
tics
by fo
liar a
pplic
atio
n. S
e-ve
rely
inju
res
woo
dy p
lant
s by
fo-
liar
appl
icat
ion,
tho
ugh
not
usu-
ally
as
effe
ctiv
e as
hor
mon
e-ty
pehe
rbic
ides
, ex
cept
on
lant
ana.
Sev
eral
woo
dy s
peci
es v
ery
sen-
sitiv
e to
cut
-sur
face
tre
atm
ents
,in
clu
din
g
Ch
ine
se
ba
nya
n,
kara
kanu
t, pa
perb
ark,
rose
appl
e.
Fol
iar
spot
spr
ay a
ndcu
t-su
rfa
ce i
n p
as-
ture
s a
nd
fo
rest
s.B
roa
dca
st s
pra
y in
fore
sts
an
d i
n p
as-
ture
s fo
r p
ast
ure
reno
vatio
n.
Ab
sorb
ed
th
rou
gh
fo
liag
e.
Ra
infa
ll w
ithin
six
ho
urs
of
appl
icat
ion
may
was
h gl
ypho
-sa
te o
ff th
e fo
liage
and
redu
ceef
fect
iven
ess.
Tra
nslo
cate
dre
adily
in
phlo
em.
Mod
e of
actio
n: d
isru
pts
synt
hesi
s of
aro
ma
tic
am
ino
aci
ds
an
dth
us o
f pr
otei
ns.
Sym
ptom
ssl
ow to
app
ear.
So
stro
ngly
ads
orbe
d to
soi
lsas
to
rend
er it
inac
tive
imm
e-di
atel
y. P
oses
no
grou
nd w
a-te
r co
nta
min
ati
on
th
rea
t.R
eadi
ly d
ecom
pose
d by
soi
lm
icro
orga
nism
s. B
ecau
se o
fst
rong
ads
orpt
ivity
, ha
lf-lif
e in
soil
47 d
ays
but
non-
phyt
o-to
xic.
Lo
w t
oxi
city
. O
ral
LD
50 f
or
rats
49
00
mg/
kg.
Chr
onic
tox
-ic
ity s
tudi
es o
n ra
tsan
d do
gs f
ed u
p to
300
ppm
per
day
for
2 ye
ars
prod
uced
no
effe
cts.
Unr
estr
icte
d.G
razi
ng:
For
lact
atin
g an
i-m
als,
with
hold
14
days
af-
ter
spo
t a
pp
lica
tio
n,
56
days
afte
r bro
adca
st a
ppli-
catio
n. F
or m
eat
anim
als,
one
day
with
hold
ing
afte
rsp
ot a
pplic
atio
n, 5
6 da
ysaf
ter b
road
cast
app
licat
ion.
Ap
plic
atio
nB
ehav
ior
in p
lan
tsB
ehav
ior
in s
oil
Toxi
city
Reg
ula
tio
ns
UseDic
amb
aB
anve
l®, a
min
e sa
lt; C
larit
y®, D
GA
sal
t; V
eter
an® 1
0G (
BA
SF
)V
anqu
ish®
, DG
A s
alt (
Syn
gent
a)M
ixtu
res
Ap
plic
atio
nB
ehav
ior
in p
lan
tsB
ehav
ior
in s
oil
Toxi
city
Reg
ula
tio
ns
Use
Pos
tem
erge
nce
cont
rol o
f bro
a-d
lea
f w
ee
ds
incl
ud
ing
so
me
woo
dy p
lant
s in
pas
ture
s an
dna
tura
l ar
eas.
Pol
ygon
aceo
usw
eeds
(kam
ole,
spi
ny e
mex
) are
very
sen
sitiv
e. B
ur b
ush,
chr
ist-
mas
berr
y, f
alse
ele
phan
tsfo
ot,
guav
a ar
e se
nsiti
ve.
Fol
iar
spra
y, 0
.25–
8lb
/acr
e in
SV
R o
f 2–
40 g
al/a
cre.
Cut
-sur
face
Ab
sorb
ed
by
fol i
ag
e a
nd
root
s. T
rans
loca
tes
read
ily in
xyle
m a
nd p
hloe
m. H
orm
one
type
her
bici
de,
caus
es c
urv-
ing,
ben
ding
of s
tem
s, c
urlin
go
f le
ave
s. A
ccu
mu
late
s in
grow
ing
poin
ts i
n st
ems
and
root
s.
Low
to
med
ium
lea
chin
g po
-te
ntia
l in
soi
ls b
ut h
alf
life
isle
ss th
an l4
day
s in
war
m m
oist
soils
.
Low
tox
icity
to
fish,
bird
s an
d m
amm
als.
LD50
rat
s: 2
629
mg/
kg.
Unr
estr
icte
d.G
razi
ng:
For
lac
tatin
g an
i-m
als
on p
astu
res
trea
ted
with
≤1 ⁄2
lb/a
cre,
7 d
ays
with
-ho
ldin
g; 1
lb/a
cre,
21
days
;2
lb/a
cre,
40
days
; and
8 lb
/ac
re, 6
0 da
ys. F
or m
eat a
ni-
mal
s, n
o w
ithho
ldin
g bu
t re-
mo
ve a
nim
als
fro
m p
as-
ture
s tr
eate
d w
ith ≥
2 lb
/acr
e30
day
s be
fore
sla
ught
er.
28
Herbicidal Weed Control Methods for Pastures and Natural Areas of Hawaii
Hex
azin
on
eV
elpa
r 90
W®, 9
0% w
etta
ble
pow
der
(DuP
ont)
Vel
par
L®, 2
5% m
isci
ble
liqui
d (D
uPon
t)P
rono
ne P
ower
Pel
lets
®, l
arge
pel
lets
for
grid
app
licat
ions
(D
uPon
t)
Ap
plic
atio
nB
ehav
ior
in p
lan
tsB
ehav
ior
in s
oil
Toxi
city
Reg
ula
tio
ns
Use
Non
sele
ctiv
e co
ntro
l of w
eeds
inpa
stur
es a
nd n
oncr
opla
nd.
Se-
lect
ivity
is a
chie
ved
by d
irect
edsp
ray
appl
icat
ions
and
by
“hot
spot
” app
licat
ions
to th
e so
il ne
arth
e ta
rget
wee
d w
here
the
root
sca
n ab
sorb
the
herb
icid
e.
App
ly V
elpa
r L in
spo
ts to
the
soil
with
an
exac
tde
liver
y gu
n ap
plic
ator
with
in 3
ft
of s
tem
at
2–4
ml p
er in
ch s
tem
dia
met
er, n
ot to
exc
eed
0.33
gal
per
acr
e pe
r ye
ar (
300
1-in
ch s
tem
equi
vale
nts
per
acre
). W
here
mul
tiple
app
li-ca
tions
are
req
uire
d, a
pply
at o
ppos
ite s
ides
of p
lant
. Do
not a
pply
to s
tand
ing
wat
er, i
rri-
gatio
n di
tche
s or
mar
shes
as
hexa
zino
ne is
very
sol
uble
. Do
not a
pply
to th
ick
clay
soi
ls.
Do
not
appl
y ne
ar d
esira
ble
plan
ts (
with
in a
dist
ance
equ
al to
3 ti
mes
the
heig
ht o
r can
opy
diam
eter
, whi
chev
er is
gre
ater
). B
oth
Vel
par
L an
d V
elpa
r 90
W m
ay b
e ap
plie
d to
the
foli-
age
of ta
rget
pla
nts
in s
pot a
pplic
atio
n. H
ow-
ever
, th
e sp
raye
d ar
ea w
ill r
emai
n ba
re f
orse
vera
l mon
ths.
Pro
none
Pow
er P
elle
ts m
aybe
app
lied
in 3
-ft
grid
app
licat
ions
to
targ
eton
e or
mor
e pl
ants
.
Abs
orbe
d by
root
s an
dfo
l iag
e.
Tra
nsl
oca
tes
via
the
xyle
m.
Inhi
bits
phot
osyn
thes
is.
Mob
ile a
nd s
uffic
ient
lyp
ers
iste
nt
(ha
lf-l i f
e 9
0da
ys)
to h
ave
pote
ntia
lfo
r g
rou
nd
wa
ter
con
-ta
min
atio
n in
hig
h ra
in-
fall
area
s.
Lo
w t
oxi
city
to
fish,
wi ld
l ife
and
ma
mm
als
. L
D5
0
rats
l690
mg/
kg.
Unr
estr
icte
d.G
razi
ng: w
ithho
ldfo
r 30
day
s af
ter
appl
icat
ion.
Ap
plic
atio
nB
ehav
ior
in p
lan
tsB
ehav
ior
in s
oil
Toxi
city
Reg
ula
tio
ns
UseIm
azap
yrA
rsen
al® (
BA
SF
)C
hopp
er® (
BA
SF
)C
hopp
er R
TU
®, r
eady
-to-
use
(BA
SF
)
Non
sele
ctiv
e pr
eem
er-
ge
nce
an
d p
ost
em
er-
genc
e co
ntro
l of
gra
ssan
d br
oadl
eaf
wee
ds i
nfo
rest
s an
d w
ildlif
e op
en-
ings
.
Fol
iar 1
lb a
ctiv
e/ac
re, b
asal
bar
k,st
umps
.
Str
ongl
y ad
sorb
ed in
aci
dso
ils a
nd h
igh
clay
and
or-
gani
c m
atte
r so
ils.
Doe
sno
t le
ach.
No
runo
ff in
tofo
rest
str
ea
ms.
Ra
pid
lyd
eg
rad
es
in
sha
llo
wpo
nds.
Rea
dily
abs
orbe
d vi
a fo
li-a
ge
an
d r
oo
ts.
Tra
nsl
o-
cate
s vi
a x
yle
m a
nd
ph
-lo
em.
Inte
rfer
es w
ith s
yn-
thes
is o
f pro
tein
s.
Low
toxi
city
to fi
sh,
wild
life
and
mam
-m
als
. L
D5
0 r
ats
,50
00+
mg/
kg.
Unr
estr
icte
d.W
eeds
can
dev
elop
cro
ss r
e-si
stan
ce b
etw
een
sulfo
nylu
reas
(e.g
., m
ets
ulfu
ron
, su
lfom
et-
uron
) and
imid
azol
inon
es (e
.g.,
imaz
apyr
) if
any
one
or c
ombi
-na
tion
of th
ese
type
s of
che
mi-
cals
are
use
d re
peat
edly
ove
r4–
6 ye
ars.
The
se h
erbi
cide
ssh
ould
be
alte
rnat
ed w
ith h
er-
bici
des
with
diff
eren
t mod
es o
fac
tion.
Pre
cau
tio
ns
29
UH–CTAHR
MC
PA
MC
P A
min
e 4®
(C
lean
Cro
p)
Sel
ectiv
e co
ntro
l of
bro
adle
afw
eeds
(e.
g.,
joee
, M
adag
asca
rra
gwor
t, tr
opic
age
ratu
m,)
and
som
e se
nsiti
ve w
oody
wee
dssu
ch a
s gu
ava
in p
astu
res,
for
-es
ts a
nd n
on-c
rop
area
s.
Fol
iar,
1-2
lb/a
cre
and
cut
surf
ace
in
pa
s-tu
res.
Non
-cro
p la
ndup
to 3
lb/a
cre.
Leg
umes
sen
sitiv
e.
Ap
plic
atio
nB
ehav
ior
in p
lan
tsB
ehav
ior
in s
oil
Toxi
city
Reg
ula
tio
ns
Use
Rea
dlily
abs
orbe
d by
leav
es.
Phl
oem
mob
ile.
Not
per
sist
ent.
Mob
ility
not
apr
oble
m g
iven
sho
rt h
alf-
life
of6
days
in w
arm
, moi
st s
oils
.
Slig
htly
to
xic.
Ora
lLD
50 in
mic
e 65
0 m
g/kg
bod
ywei
ght.
Unr
estr
icte
d.R
emov
e m
eat
anim
als
tobe
sla
ught
ered
from
trea
ted
lan
d
on
e
we
ek
be
fore
slau
ghte
r or a
fter M
CP
A a
p-pl
icat
ion.
Do
not g
raze
milk
an
ima
ls o
n t
rea
ted
la
nd
with
in 1
wee
k of
trea
tmen
t.
Met
sulf
uro
nE
scor
t®, 6
0% d
ry fl
owab
le (
DuP
ont)
Ally
®, 6
0% d
ry fl
owab
le (
DuP
ont)
Sel
ectiv
e co
ntro
l of
di-
cots
in
pa
stu
res
an
dno
ncro
plan
d. K
ahili
gin
-ge
r, y
ello
w g
inge
r an
dw
hite
gin
ger v
ery
sens
i-tiv
e (0
.5 o
z. p
rodu
ct /
acre
).
Fol
iar
spra
y 0.
06-0
.45
oz a
ctiv
e/ac
re,
with
an
effe
ctiv
e su
rfac
tant
, in
20-1
00 g
al/a
cre.
Ver
y lo
wdo
ses
effe
ctiv
e. E
xtre
me
prec
autio
ns s
houl
d be
take
n to
pre
vent
drif
t and
in c
lean
ing
equi
pmen
t.W
eeds
can
dev
elop
cro
ss r
esis
tanc
e be
twee
nsu
lfony
lure
as (
e.g.
, m
etsu
lfuro
n, s
ulfo
met
uron
)an
d im
idaz
olin
ones
(e.
g.,
imaz
apyr
) if
any
one
or c
ombi
natio
n of
thes
e ty
pes
of c
hem
ical
s ar
eus
ed r
epea
tedl
y ov
er 4
-6 y
ears
.
Rea
dily
abs
orbe
d by
foli-
age
and
root
s. T
rans
lo-
cate
s re
adily
in th
e xy
lem
and
less
so
in th
e ph
loem
.
Ads
orpt
ion
to c
lays
is lo
w;
leac
habl
e, b
ut b
iode
gra-
datio
n is
rapi
d. H
alf-
life
isl-6
wee
ks.
Low
toxi
city
tofis
h, w
ildlif
e an
dm
amm
als.
LD
50
rats
>50
00 m
g/kg
.
Unr
estr
icte
d.N
o gr
azin
g re
stric
-tio
ns.
Ap
plic
atio
nB
ehav
ior
in p
lan
tsB
ehav
ior
in s
oil
Toxi
city
Reg
ula
tio
ns
Use Par
aqu
atO
rtho
Par
aqua
t® C
L (C
hevr
on)
Gra
mox
one®
(Z
enec
a)
Non
-sel
ectiv
e. A
pply
as
folia
rsp
ray
for
supp
ress
ion
of e
xist
-in
g ve
geta
tion
e.g.
, fo
r pa
stur
ere
no
vati
on
. M
atu
re
pla
nts
read
ily r
ecov
er fr
om tr
eatm
ent.
Fol
iar
spra
y.V
ery
rapi
dly
abso
rbed
by
foli-
age.
Ver
y re
sist
ant
to w
ash-
ing
by r
ain.
Mod
e of
act
ion:
Con
tact
. D
estr
uctio
n of
cel
lm
embr
anes
in
the
pres
ence
of s
unlig
ht. N
o br
eakd
own
ofpa
raqu
at in
pla
nts.
Str
on
gly
an
d i
mm
ed
iate
lyad
sorb
ed t
o cl
ay m
iner
als
inso
ils.
Soi
l-bou
nd p
araq
uat
ispe
rsis
tent
but
bio
logi
cally
inac
-tiv
e. It
will
be
slow
ly d
egra
ded.
Mo
de
rate
ly t
oxi
c,a
cute
ora
l L
D5
0 i
nra
ts i
s 1
20
mg
/kg
.C
hron
ic t
oxic
ity t
ri-
als,
2 y
ears
at u
p to
l70
pp
m p
ara
qu
at
per d
ay p
rodu
ced
noef
fect
in r
ats.
Res
tric
ted
use,
irre
vers
ibly
toxi
c if
swal
low
ed.
Spe
cial
perm
it fr
om th
e H
awai
i De-
part
men
t of
Agr
icul
ture
re-
quire
d.
Ap
plic
atio
nB
ehav
ior
in p
lan
tsB
ehav
ior
in s
oil
Toxi
city
Reg
ula
tio
ns
Use
30
Herbicidal Weed Control Methods for Pastures and Natural Areas of Hawaii
Pic
lora
mTo
rdon
22K
®, p
otas
sium
sal
t (D
ow A
groS
cien
ces)
Woo
dy p
lant
con
trol
, fo
liar
and
cut-
surf
ace
appl
icat
ions
in p
as-
ture
s. G
rass
es to
lera
nt, c
ruci
fer-
ous
plan
ts (
cabb
age
fam
ily)
tol-
eran
t. W
ide
spec
trum
of
dico
tsp
eci
es
susc
ep
tible
in
clu
din
gbl
ack
wat
tle,
cact
us,
cats
claw
,ch
ristm
asbe
rry,
gor
se,
lant
ana,
faya
tree
, hila
hila
, jav
a pl
um, k
oaha
ole,
ros
eapp
le.
Fol
iar
spra
y, c
ut-
surf
ace
appl
icat
ion.
Rea
dily
abs
orbe
d by
fol
iage
and
by r
oots
. R
eady
tra
nslo
-ca
tion
in x
ylem
and
phl
oem
.M
ode
of a
ctio
n: h
orm
onal
.
Can
be
pers
iste
nt, h
alf-
life
20-
300
days
, and
mob
ile in
san
dy,
low
org
anic
mat
ter
soils
. B
e-ca
use
of p
ersi
sten
ce, e
xtre
me
caut
ion
shou
ld b
e ex
erci
sed
toav
oid
drift
and
oth
er f
orm
s of
cont
amin
atio
n of
cro
plan
d an
dsi
mi la
rly s
ensi
tive
non-
targ
etar
eas.
Thi
s in
clud
es k
eepi
ngl i
vest
ock
gra
zin
g r
ece
ntl
ytr
ea
ted
pa
stu
res
fro
m c
rop
-la
nd
. P
iclo
ram
w
ill
pa
ssth
roug
h an
imal
s ra
pidl
y an
dun
alte
red.
Pic
lora
m is
sen
sitiv
eto
pho
tode
com
posi
tion.
Low
ord
er o
f tox
icity
.O
ral
LD50
for
rat
s is
8200
mg/
kg. C
hron
icto
xici
ty
tria
ls
(2ye
ars
, l5
0 m
g/k
g/
da
y) o
n r
ats
an
dd
og
s p
rod
uce
d n
oef
fect
s.
Res
tric
ted
use.
Spe
cial
per
-m
it fr
om
Ha
wa
ii D
ep
art
-m
en
t o
f A
gri
cult
ure
re
-qu
ired.
Spo
t spr
ayin
g on
ly.
Ha
zard
to
n
on
-ta
rge
tpl
ants
, gr
ound
wat
er c
on-
tam
inat
ion
pote
ntia
l.G
razi
ng:
For
lact
atin
g an
i-m
als
14 d
ays
with
hold
ing.
For
mea
t an
imal
s on
pas
-tu
res
trea
ted
with
up
to 1
lb/
acre
no
with
hold
ing,
but
re-
mov
e 3
days
bef
ore
slau
gh-
ter
durin
g th
e 2
wee
ks f
ol-
low
ing
trea
tmen
t.
Ap
plic
atio
nB
ehav
ior
in p
lan
tsB
ehav
ior
in s
oil
Toxi
city
Reg
ula
tio
ns
Use Su
lfo
met
uro
nO
ust®
, dis
pers
able
gra
nule
s (D
uPon
t)
Non
sele
ctiv
e pr
eem
erge
nce
and
post
emer
genc
e co
ntro
lof
wee
ds in
nat
ural
are
as.
Fo
liar
2.2
5–
8 o
zac
tive/
acre
.A
bsor
bed
via
root
s an
dfo
liage
. Tr
ansl
ocat
es i
nbo
th x
ylem
and
phl
oem
.In
hibi
ts p
rote
in s
ynth
e-si
s.
Mob
ility
in a
cid
soils
and
high
org
anic
mat
ter
soils
po
ore
r th
an
in
alk
alin
eso
ils a
nd
lo
w o
rga
nic
mat
ter
soils
. Soi
l hal
f-lif
ein
aci
d so
ils 2
0–28
day
s.
Low
tox
icity
to
fish,
bird
s an
d m
amm
als.
Ora
l L
D5
0 i
n r
ats
gre
ate
r th
an
50
00
mg/
kg.
Bec
ause
sul
fom
etur
on i
s ef
fect
ive
at l
owra
tes,
avo
id d
rift a
nd a
pplic
atio
n to
bar
e so
ilw
here
win
d ca
n bl
ow tr
eate
d so
il on
to s
en-
sitiv
e pl
ants
. W
eeds
can
dev
elop
cro
ss r
e-si
stan
ce b
etw
een
sulfo
nylu
reas
(e.
g.,
met
-su
lfuro
n, s
ulfo
met
uron
) and
imid
azol
inon
es(e
.g.,
imaz
apyr
) if
any
one
or c
ombi
natio
nof
thes
e ty
pes
of c
hem
ical
s ar
e us
ed re
peat
-e
dly
ove
r 4
–6
ye
ars
. T
he
se h
erb
icid
es
shou
ld b
e al
tern
ated
with
her
bici
des
with
dif-
fere
nt m
odes
of a
ctio
n.
Ap
plic
atio
nB
ehav
ior
in p
lan
tsB
ehav
ior
in s
oil
Toxi
city
Pre
cau
tio
ns
Use
31
UH–CTAHR
Tric
lop
yrG
arlo
n 3A
®, a
min
e sa
lt (D
ow A
groS
cien
ces)
Gar
lon
4®, e
ster
(D
ow A
groS
cien
ces)
Pat
hfin
der
II, e
ster
, rea
dy-t
o-us
e (D
ow A
groS
cien
ces)
Red
eem
®, a
min
e sa
lt (D
ow A
groS
cien
ces)
Rem
edy
, est
er (
Dow
Agr
oSci
ence
s)
Con
trol
s br
oadl
eave
s in
clud
ing
woo
dyp
lan
ts i
n p
ast
ure
s a
nd
na
tura
l a
rea
s.C
hri
stm
asb
err
y, d
ow
ny
rose
myr
tle
,F
orm
osan
koa
, gor
se, g
uava
, str
awbe
rry
guav
a, h
ighb
ush
blac
kber
ry,
Java
plu
m,
me
last
om
a,
nig
ht-
blo
om
ing
ce
reu
s,th
imbl
eber
ry,
velv
et t
ree,
yel
low
Him
a-la
yan
ra
spb
err
y se
nsi
tive
. D
ow
ny
rose
myr
tle, l
anta
na, M
adag
asca
r rag
wor
tto
lera
nt o
f fol
iar a
pplic
atio
ns. M
any
woo
dysp
ecie
s se
nsiti
ve t
o cu
t-su
rfac
e or
bas
alba
rk a
pplic
atio
ns in
clud
ing
lant
ana,
kia
we,
dow
ny r
osem
yrtle
.
Fol
iar
spra
y,b
asa
l b
ark
(est
er)
an
dcu
t-su
rfac
e.
Rea
dily
abs
orbe
d by
folia
ge
an
d r
oo
ts.
Tran
sloc
ates
in
the
ph
loe
m.
Mo
de
of
actio
n: h
orm
onal
.
Mob
ile in
soi
ls. D
e-gr
aded
by
mic
roor
-ga
nism
s an
d su
n-lig
ht.
Ave
rage
hal
flif
e: 1
0–46
day
s.
Low
ord
er o
f to
x-ic
ity.
Acu
te o
ral
LD
50 f
or
rats
is
2l40
mg/
kg.
Unr
estr
icte
d.G
razi
ng
: F
or
lact
atin
g a
nim
als
on
pa
stu
res
trea
ted
with
up
to 2
lb/
acre
, 14
day
s w
ithho
ld-
ing,
for
rat
es b
etw
een
2–6
lb/a
cre,
no
graz
ing
until
the
next
gro
win
g se
ason
. For
oth
er li
vest
ock
on p
astu
res
trea
ted
with
up
to 2
lb/a
cre,
no
with
-ho
ldin
g bu
t rem
ove
thre
e da
ys b
efor
e sl
augh
ter
durin
g ye
ar o
f ap
plic
atio
n. O
n pa
stur
es t
reat
edw
ith r
ates
bet
wee
n 2–
6 lb
/acr
e, 1
4 da
ys w
ith-
hold
ing
and
rem
ove
thre
e da
ys b
efor
e sl
augh
ter
durin
g ye
ar o
f ap
plic
atio
n. I
f le
ss t
han
25%
of
the
past
ure
is tr
eate
d, n
o gr
azin
g re
stric
tion.
Ap
plic
atio
nB
ehav
ior
in p
lan
tsB
ehav
ior
in s
oil
Toxi
city
Reg
ula
tio
ns
UseTeb
uth
iuro
nS
pike
20
P®, p
elle
ts (
Dow
Agr
oSci
ence
s)
Fo
r co
ntr
ol
of
dic
ots
in
clu
din
gw
oody
pla
nts
by s
oil a
pplic
atio
nsin
pas
ture
s an
d w
ildlif
e op
enin
gs.
Eff
ect
ive
on
ch
rist
ma
sbe
rry,
gu
ava
, st
raw
be
rry
gu
ava
, ko
ah
ao
le,
Ma
da
ga
sca
r ra
gw
ort
,sh
oe
bu
tto
n a
rde
sia
. P
oo
r o
nd
ow
ny
rose
myr
tle
, fa
yatr
ee
,F
orm
osan
koa
, gor
se.
App
licat
ion
ofg
ran
ule
s to
grou
nd, 0
.75–
3.0
lb a
ctiv
e/ac
re.
Abs
orbe
d th
roug
h th
ero
ots,
poo
rly th
roug
h fo
-l ia
ge.
Rea
dily
tra
nslo
-ca
ted
in x
ylem
. Mod
e of
actio
n: p
hoto
synt
hesi
sin
hibi
tor.
Ver
y pe
rsis
tent
in s
oils
,ha
lf-lif
e of
l2–l
5 m
onth
s.M
ore
pers
iste
nt i
n dr
yso
i ls a
nd h
igh
orga
nic
mat
ter s
oils
. Poo
r mob
il-ity
in s
oils
.
Slig
htly
toxi
c. O
ral
LD
50 f
or
rats
is
644
mg/
kg. T
hree
gene
ratio
ns fe
ed-
ing
tria
ls in
dica
teno
toxi
city
to ra
ts.
Unr
estr
icte
d.G
razi
ng: U
p to
20
lb p
rod
uct
/acr
e,
no w
ithho
ldin
g.
Ap
plic
atio
nB
ehav
ior
in p
lan
tsB
ehav
ior
in s
oil
Toxi
city
Reg
ula
tio
ns
Use
Hig
her
dose
s, 1
5 lb
prod
uct/a
cre
or h
ighe
r ,ca
n in
jure
gra
sses
.
Pre
cau
tio
ns
32
Herbicidal Weed Control Methods for Pastures and Natural Areas of Hawaii
Appendix 2.Common and Botanical Namesof Weeds Mentioned in the Text
Listed here are the botanical names of weeds of Hawaiimentioned in this publication. For additional informa-tion on these weeds, see Wagner et al.(110), Neal(81), andHaselwood et al.(41). Color photographs of some of theseweeds may be found in Pratt(91) or Whistler(115). Color
photos and management notes may be found in Lorenziand Jeffery(63), Motooka et al.(78), and in the forthcomingCTAHR publication, Weeds of pastures and natural ar-eas of Hawaii and their management, by Motooka etal., in preparation.
Common name Botanical name
ageratum, tropic Ageratum conyzoidesapple-of-Sodom Solanum linnaeanumardesia, shoebutton Ardesia ellipticabanyan, Chinese Ficus microcarpablackberry, highbush Rubus argutusblack wattle Acacia mearnsiibur bush Triumfetta rhomboideacactus, prickly pear Opuntia ficus-indicaCaliforniagrass Brachiaria muticacatsclaw Caesalpinia decapetalachristmasberry Schinus terebinthifoliusdowny rosemyrtle Rhodomyrtus tomentosaelephantsfoot, false Elephantopus spicatusemex, spiny Emex spinosafaya tree Myrica fayaFormosan koa Acacia confusafountaingrass Pennisetum setaceumginger, kahili Hedychium gardnerianumginger, white Hedychium coronariumginger, yellow Hedychium flavescensgorse Ulex europaeusguava Psidium guajavaguava, strawberry Psidium cattleianumguineagrass Panicum maximumhamakua pamakani Ageratina ripariahilahila Mimosa pudicahuehue haole Passiflora suberosa
Common name Botanical name
java plum Syzygium cuminiJob’s tears Coix lacharyma-jobijoee Stachytarpheta dichotomakamole Polygonum glabrumkarakanut Corynocarpus laevigatuskiawe Prosopis pallidakoa haole Leucaena leucocephalalantana Lantana camaraMadagascar ragwort (fireweed) Senecio madagascariensisMaui pamakani Ageratina adenophoraMauritius hemp Furcraea foetidamelastoma Melastoma candidummolucca albizia Paraserianthes falcatariamorningglory, Indian Ipomea indicanightblooming cereus Hylocereus undatuspalmgrass Setaria palmifoliapaperbark Melaleuca quinquenervapluchea, Indian Pluchea indicaragweed parthenium Parthenium hysterophorusraspberry, yellow Himalayan Rubus ellipticusroseapple Syzygium jambosSacramento bur Triumfetta semitrilobasourbush Pluchea carolinensisthimbleberry Rubus rosaefoliusturkeyberry Solanum torvumvelvet tree Miconia calvescens
33
UH–CTAHR
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2. Ames, B.N. 1983. Dietary carcinogens and anticarcinogens. Sci-ence 221(4017):1256–1264.
3. Ames, B.N. 1993. Science and the environment: facts vs. phan-toms. Priorities winter:42–43.
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5. Amor, R.L. 1975. Ecology and control of blackberry (Rubusfruticosis L. agy.) IV. Effect of single and repeated applicationsof 2,4,5-T, picloram, and aminotriazole. Weed Res. 15:39–45.
6. Amor, R.L. 1975. Ecology and control of blackberry (Rubusfruticosus L. agy.); V. Control by picloram granules. Weed Res.15:47–52.
7. Amor, R.L., and R.G. Richardson.1980. The biology of Austra-lian weeds. 2. Rubus fruticosis L. Agy. J. Australian Inst. Agri.Sci. 46:87–97.
8. Anderson, W.P. 1983. Weed science: principles. 2nd ed. WestPubl. New York. 655p.
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10. Asher, J.E. 2001. Wildlife habitat: a compelling case for weedmanagement. Abstr., Weed Sci. Soc. Amer. 41:94–95. Greens-boro, N.C.
11. Ashton, F.M., and A.S Crafts. 1973. Mode of action of herbi-cides. Wiley, New York.
12. Badiei, A.A., E. Basler, and P.W. Santlemann. 1966. Aspects ofmovement of 2,4,5-T in blackjack oak. Weeds 14:302–305.
13. Balneaves, J.M. 1980. A programme for gorse control in for-estry using a double kill spray regime. Proc. 33rd New ZealandWeed and Pest Control Conf. pp. 170–173.
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16. Balneaves, J.M., and B.J. Frederic. 1988. Silwet M improvesperformance of glyphosate on gorse. Proc. 41st New ZealandWeed and Pest Control Conf. pp. 146–148. Aukland.
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