A practical users guide to the sulfonylurea herbicides. Sulfonylurea herbicides labeled for use on...
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A practical users guide to the sulfonylurea herbicides. BY RENEE KEESE, DAVID SPAK.AND CHRISTIAN SAIN S ulfonylurea herbicides (SUs) have been a relatively minor compo- nent of turf weed control on golf courses for many years. More recently, herbicides from this class of chemistry have been introduced at a rapid pace to the turfgrass management industry. This article will introduce the golf course turf manager to an evolving class of herbicide chemistry. Ultimately, it is the individual golf course superintendent who chooses the product that best fits the need. THE BASIC CHEMISTRY OFTHESE HERBICIDES The very first practical herbicides were discovered in the early 1940s for broad- leaf weed control. At that time, 2,4-D was a key player, and the early herbi- cides of the phenoxy group required high use rates to achieve weed control. Sulfonylurea herbicides were first dis- covered in the mid-1970s and were initially developed for use in wheat and barley. They are important in agricul- tural crops, but until recently they have played a minor role in the arsenal of weed killers for turfgrass managers. The first commercial use of an SU in agri- cultural crops was in 1982 (chlorsul- furon). This was followed by the first turf registrations with Scotts' DMC (metsulfuron) and Lesco's TFC (chlor- sulfuron) in the early 1990s. This class of chemistry was created to have significantly lower use rates, which is important in today's environmentally conscientious world. SUs were devel- oped because of their ability to provide postemergence control of problem grassy weeds (monocots) in existing stands of turf at low active ingredient rates. The sulfonylureas, along with the imidazolinones, triazolopyrimidine, and pyrimidinyl oxybenzoates, are chemical classes that interfere with synthesis of the branched-chain (aliphatic) amino acids, referred to as ALS inhibitors. These herbicides interfere with the activity of the chloroplast enzyme acetolactate synthase (ALS).This enzyme is vital to the formation of valine, leucine, and isoleucine, amino acids found only in plants. The enzyme is blocked, preventing development of essential amino acids and causing the plant to starve. The tolerant plants, including turfgrasses, typically are not injured and show no symptoms. Sulfo- nylurea symptoms include growth in- hibition, chlorosis, and necrosis. Uptake occurs several hours after treatment, but symptoms may not be visible for one to two weeks. These herbicides are applied postemergence to weeds and are absorbed through the foliage and roots. Application rates are very low in this chemical class, typically an ounce or two of product per acre, with active ingredients measured in grams per acre. These herbicides differ only slightly in chemical structure, but turf tolerance, safety, and weed control spectrum may differ substantially. Therefore, it is very important to understand the unique features of each product. Table 1 lists sulfonylurea herbicides labeled for use on golf courses. Warm- and cool-season turfgrasses differ in their tolerance to SU herbi- cides. It is important that labels be read carefully and, when in doubt, contact the manufacturers or their technical representatives for specific recommen- dations. Both cultivars and environment can influence turf tolerance. The con- tinued introduction of new cultivars further emphasizes the need to test the tolerance of these new grasses before the widespread use of any herbicide. Why use this class of herbicide? In part, these products provide more weed control options than were available with other herbicides. For example: • Rogue Rye. Mature clumps of perennial ryegrass look bad and play worse. These products provide superior control of this type of grassy weed compared to other materials. • Problem Weeds. These materials help eliminate other difficult-to-control weeds, such as dallisgrass, sedges, and kyllingas, which are becoming more of a problem on golf courses each year. • Winter Weed Control. The SUs offer an alternative to other chemistries, including Roundup (glyphosate), Princep (simazine), and Kerb (prona- mide), for winter weed control. Christian Sain, golf course superinten- dent at Kingsmill Resort and Club (Williamsburg,Va.), reports that these products allow more flexibility in pesti- cide application timing. For example, through necessity, when overseeding one of their bermudagrass golf courses with ryegrass far later in the fall than normal, some Poa annua would have germinated prior to overseeding. The application of an SU product allowed them to control the Poa annua for a clean seedbed, resulting in much less Poa annua the following spring. • Spring Weed Control. It is a common practice on non-overseeded 16 GREEN SECTION RECORD
Transcript of A practical users guide to the sulfonylurea herbicides. Sulfonylurea herbicides labeled for use on...
A practical users guide to the sulfonylurea herbicides.BY R E N E E K E E S E , DAVID S P A K . A N D C H R I S T I A N SAIN
Sulfonylurea herbicides (SUs) havebeen a relatively minor compo-nent of turf weed control on golf
courses for many years. More recently,herbicides from this class of chemistryhave been introduced at a rapid pace tothe turfgrass management industry. Thisarticle will introduce the golf courseturf manager to an evolving class ofherbicide chemistry. Ultimately, it is theindividual golf course superintendentwho chooses the product that best fitsthe need.
THE BASIC CHEMISTRYOFTHESE HERBICIDESThe very first practical herbicides werediscovered in the early 1940s for broad-leaf weed control. At that time, 2,4-Dwas a key player, and the early herbi-cides of the phenoxy group requiredhigh use rates to achieve weed control.Sulfonylurea herbicides were first dis-covered in the mid-1970s and wereinitially developed for use in wheat andbarley. They are important in agricul-tural crops, but until recently they haveplayed a minor role in the arsenal ofweed killers for turfgrass managers. Thefirst commercial use of an SU in agri-cultural crops was in 1982 (chlorsul-furon). This was followed by the firstturf registrations with Scotts' DMC(metsulfuron) and Lesco's TFC (chlor-sulfuron) in the early 1990s.
This class of chemistry was created tohave significantly lower use rates, whichis important in today's environmentallyconscientious world. SUs were devel-oped because of their ability to providepostemergence control of problemgrassy weeds (monocots) in existing
stands of turf at low active ingredientrates. The sulfonylureas, along with theimidazolinones, triazolopyrimidine, andpyrimidinyl oxybenzoates, are chemicalclasses that interfere with synthesis ofthe branched-chain (aliphatic) aminoacids, referred to as ALS inhibitors.
These herbicides interfere withthe activity of the chloroplast enzymeacetolactate synthase (ALS).Thisenzyme is vital to the formation ofvaline, leucine, and isoleucine, aminoacids found only in plants. The enzymeis blocked, preventing development ofessential amino acids and causing theplant to starve. The tolerant plants,including turfgrasses, typically are notinjured and show no symptoms. Sulfo-nylurea symptoms include growth in-hibition, chlorosis, and necrosis. Uptakeoccurs several hours after treatment,but symptoms may not be visible forone to two weeks. These herbicides areapplied postemergence to weeds andare absorbed through the foliage androots. Application rates are very low inthis chemical class, typically an ounceor two of product per acre, with activeingredients measured in grams per acre.
These herbicides differ only slightlyin chemical structure, but turf tolerance,safety, and weed control spectrum maydiffer substantially. Therefore, it is veryimportant to understand the uniquefeatures of each product. Table 1 listssulfonylurea herbicides labeled for useon golf courses.
Warm- and cool-season turfgrassesdiffer in their tolerance to SU herbi-cides. It is important that labels be readcarefully and, when in doubt, contactthe manufacturers or their technical
representatives for specific recommen-dations. Both cultivars and environmentcan influence turf tolerance. The con-tinued introduction of new cultivarsfurther emphasizes the need to test thetolerance of these new grasses beforethe widespread use of any herbicide.
Why use this class of herbicide? Inpart, these products provide more weedcontrol options than were availablewith other herbicides. For example:• Rogue Rye. Mature clumps ofperennial ryegrass look bad and playworse. These products provide superiorcontrol of this type of grassy weedcompared to other materials.• Problem Weeds. These materialshelp eliminate other difficult-to-controlweeds, such as dallisgrass, sedges, andkyllingas, which are becoming more ofa problem on golf courses each year.• Winter Weed Control. The SUsoffer an alternative to other chemistries,including Roundup (glyphosate),Princep (simazine), and Kerb (prona-mide), for winter weed control.Christian Sain, golf course superinten-dent at Kingsmill Resort and Club(Williamsburg,Va.), reports that theseproducts allow more flexibility in pesti-cide application timing. For example,through necessity, when overseedingone of their bermudagrass golf courseswith ryegrass far later in the fall thannormal, some Poa annua would havegerminated prior to overseeding. Theapplication of an SU product allowedthem to control the Poa annua for aclean seedbed, resulting in much lessPoa annua the following spring.• Spring Weed Control. It is acommon practice on non-overseeded
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A sulfonylurea herbicide applied prior to fall overseeding of bermudagrass to ryegrass demonstrates
its success when a missed strip obviously stands out.
bermudagrass and zoysiagrass to sprayout winter weeds using products suchas Roundup. Timing these sprays isalways tricky. If sprayed early (in latewinter), any possible damage to thewarm-season grasses is minimized;however, this leaves time for weedslike Poa annua to germinate after theRoundup spray. By contrast, if the sprayis applied later, in an attempt to try tocontrol the spring germinating weedsand weedy grasses, this increases thepossibility of damaging warm-seasongrass that may be breaking dormancy.With SUs, golf course superintendentsnow have the option of spraying earlywith products like Roundup, and thenspraying a second time if necessary tocontrol spring germinating weeds.• Postemergence Weed Control.Depending upon the product, the SUsare labeled for the control of a long list
of weeds in actively growing bermuda-grass and other warm-season grasses,such as St. Augustinegrass and centi-pedegrass. Controlling kyllingas andother difficult weeds now becomesmore manageable.• The Environment. This uniquechemistry of herbicides requires in-credibly low use rates. Active ingredientrates are measured in grams per acre vs.ounces or pounds per acre for conven-tional herbicides. These products, as agroup, have low dermal, inhalation, andacute toxicity to mammals, fish, wild-life, and pollinators, including honeybees.• Managing the Transition of Over-seeded Ryegrass. This useful herbicidechemistry allows superintendents toeffectively manage the ryegrass transi-tion by controlling the rate and time ofapplication. Christian Sain noted that
these products provide more weed con-trol options. "The ability to controlwhen the overseeded ryegrass dies outand the bermudagrass emerges isperhaps the greatest strength of thischemistry. In the North, cool springsoften delay ryegrass transitions intoearly summer. All too often, by the timethe ryegrass is gone, the bermudagrassbarely has enough time to fill in anddevelop a healthy sod before it is timeto overseed in the fall. I'm convincedthis delay weakens the bermudagrass,especially in shaded and wet areas. I cannow look at the calendar and countback at least 100 days from the time Iplan to overseed in the fall and use thatdate to spray out the rye in the spring."
THE ONE-HUNDRED-DAYGUIDELINETurf managers across the U.S. are usingthe "100-day guideline" as the mini-mum amount of time needed for goodbermudagrass growth prior to fall over-seeding. Dr. Fred Yelverton, NorthCarolina State University, states, "Basedon field observations where bermuda-grass is overseeded with perennial rye-grass, it generally takes bermudagrassapproximately 100 days to recover.Ground cover can be obtained in lessthan 100 days, but rhizome and stolonrecovery will take about 100 days. Weknow this from overseeding removaltrials where perennial ryegrass does notdie out quickly enough for bermuda-grass recovery. This is why I recommenda transition aide (herbicide) in areaswhere 100 days of bermudagrass growth"without perennial ryegrass competitioncannot otherwise be obtained."
POTENTIAL FOR TRACKINGAND MOVEMENTMany sulfonylurea herbicides are verysafe on warm-season grasses. However,they can be lethal to cool-season grassessuch as ryegrass, bentgrass, Poa annua,tall fescue, and Poa trivialis. The applica-tion of these herbicides in proximity tosensitive species, such as bentgrass putt-
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Table 1Sulfonylurea herbicides labeled for use on golf courses.
TradeName
Corsair
Revolver
Manage
Manor
Certainty
Monument
TranXitGTA
ActiveIngredient
chlorsulfuron
foramsulfuron
halosulfuron
metsulfuron
sulfosulfuron
trifloxysulfuron
rimsulfuron
Manufacturer
Riverdale
Bayer EnvironmentalScience
Monsanto
Riverdale
Monsanto
Syngenta
DuPont
LabeledTurfgrasses
bermudagrass,St. Augustinegrass,centipedegrass,zoysiagrass,bahiagrass
bermudagrass andzoysiagrass
Numerous cool-and warm-seasongrasses
Kentucky bluegrass,fine fescue,bermudagrass,St. Augustinegrass,zoysiagrass, andcentipedegrass
bermudagrass,St. Augustinegrass,zitsuagrass,centipedegrass,kikuyugrass
bermudagrass andzoysiagrass
bermudagrass,zoysiagrass,centipedegrass(temporarilysuppresses Tifwaybermudagrass)
WeedControl TransitionSpectrum Aid
Various grassand broadleafweeds
Annual and Yesperennial cool-season grasses,including Poo annuaand goosegrass
Yellow and Yespurple nutsedge,kyllinga
Annual and Yesperennialgrasses andbroadleaves
Annual andperennial sedges,grass andbroadleaf weeds
Sedges, grasses, Yesbroadleaf weeds,and kyllinga
Annual and Yesperennial cool-season grasses,including Poo annua
UniqueFeatures
dallisgrasssuppression
bahiagrasscontrol
Johnsongrasscontrol
Torpedograsssuppression,dichondracontrol
RyegrassOverseedingRestrictions
2 weeks
7- 10 days,but not insouthwesternU.S.
6 weeks
ing greens, on an otherwise bermuda-grass golf course should be made underconditions that minimize the potentialfor drift, tracking, and soil movement(if the product has soil activity).Thebottom line is to know your productand read the label before making anapplication.
IN CONCLUSIONThis chemistry of herbicides has beenaround for a long time, but through acombination of factors, Sulfonylureaherbicides are just now becoming asignificant part of the weed controlarsenal. Although these products may besimilar chemically, they vary widely intheir safety and utility on different
grasses. As with all products, care shouldbe taken to study the conditions athand and select the least toxic productavailable to control a pest problem.
FOOTNOTEThe primary emphasis of this article isthe option for using the Sulfonylureachemistry of herbicides on warm-season grasses, primarily bermudagrass.It should be noted that other productsfrom this and related groups can beused on cool-season grasses. This under-scores the uniqueness of these materials.Monsanto's SU (sulfosulfuron) andVelocity (bispyribac-sodium) can beused on cool-season grasses for weedcontrol, including difficult-to-control
weed grasses like Poa annua and Poatrivialis. Velocity is an ALS inhibitor butnot a Sulfonylurea, although it acts likeone. Space does not allow for completediscussion of this equally exciting aspectof weed control. Contact the individualmanufacturers, their technical represen-tatives, state university extension per-sonnel, or your regional USGA agrono-mist for more information.
DR. RENEE KEESE, R&D scientist,Syngenta Crop Protection, Indianapolis, Ind.DR. DAVID SPAK, Field Development &Technical Services, Bayer EnvironmentalScience, New Holland, Pa. CHRISTIANSAIN, director of golf course maintenance,Kingsmill Resort & Spa, Williamsburg, Va.
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