Kentucky Pest News, July 9, 2013

7/28/2019 Kentucky Pest News, July 9, 2013

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Online at:www.uky.edu/KPN

Number 1347 July 9, 2013

CORN-Keep a Watch for Gray Leaf Spot

SOYBEANKudzu Bug Not Crying Wolf

TOBACCO

-Disease Update for the Week of July 8-Tobacco Hornworm Control

PEST OF HUMANS-Potential Pest Problems Following Extended

Rains

FUNGICIDES-Some Principles of Fungicide Resistance V:

Ecological Fitness

CORN

Keep a Watch for Gray Leaf SpotBy Paul Vincelli, Extension Plant Pathologist

This is just a reminder of the factors that favor apositive yield response from a strobilurinfungicide in corn. Figure 1 lays this out

graphically.

Figure 1. Factors that increase the probability of benefit

from a foliar fungicide in corn. The top five factors are often

the most important.

Disease pressure is, of course, the primary factordetermining the probability of a benefit from afoliar fungicide in corn. With all the rain this

season, gray leaf spot (Figure 2) may be wiselyactive. Producers may wish to scout fields forevidence of disease activity.

Scouting guidelines for gray leaf spot originated

from Iowa State University, and many universitieshave adopted these with little to no modification.They are:

1. Consider a fungicide application if:a. The hybrid is rated as susceptible ormoderately susceptible, AND,

b. 50 percent of the plants in a field havedisease lesions present on the thirdleaf below the ear leaf or higher prior

to tasseling.2. Consider a fungicide application if:

a. The hybrid is rated as moderatelyresistant, AND,

b. 50 percent of the plants in a field havedisease lesions present on the thirdleaf below the ear leaf or higher prior

to tasseling, AND,c. Additional factors or conditions that

favor disease development are present

(See Figure 1)

Lexington, KY 40546
http://www.uky.edu/KPNhttp://www.uky.edu/KPNhttp://www.uky.edu/KPNhttp://www.uky.edu/KPN


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These are approximate guidelines, and the diseasecan be unpredictable. Nevertheless, these

guidelines can be helpful tools in making rationalspray decisions.

Figure 2. Young lesions of gray leaf spot of corn. Image of

Doug Jardine, Kansas State University.

SOYBEAN

Kudzu Bug Not Crying WolfBy Douglas W. Johnson, Extension Entomologist

Any number of you are aware that I have beentalking about the arrival of Kudzu bug inKentucky for the past two years. Fortunately, sofar as I know, this invasive pest has not arrived in

the commonwealth. Nevertheless, it approachesever nearer to our area. Dr. Scott Stewart, mycolleague in Tennessee, is now dealing withKudzu bug infestations in several southeasternTennessee counties (See his article through the

link immediately below).

(See:http://news.utcrops.com/2013/06/kudzu-bugs-in-soybean/)

Like Kentucky, most of Tennessees soybean

production is in the western portion of the state.None the less, this activity in eastern Tennessee

provides a foothold in our area and represents theinfestation closest to Kentucky. In addition, this

probably represents establishment (a locallyoverwintered population) and not introduction

because this pest was discovered in eastern

Tennessee in previous years.

It is as yet unknown how important this pest willbe in Kentucky soybeans. However, it has becomea major pest within two years of discovery in the

soybean production states to the south of us. I seeno reason to believe that this will not be the case

in Kentucky. It is therefore important for us tokeep a watch out for this pest. My guess is that it

will first appear in counties with kudzu along theinterstate corridors that handle traffic from eastTennessee, the Carolinas, Georgia and Alabama.This includes I-75, I-65 and I-24. Producers andother interested parties would do well to look forthis bug in kudzu and soybeans that border these

highways.

Though kudzu bug is new to the United States, notknown to be present in Kentucky, and has no otherspecies in the same family in the Americas, it

should be pretty easy to identify. It is an odd

looking creature that doesnt look like anythingyou are used to seeing in soybeans. Its closestrelatives would be the insects we commonly callstinkbugs. There are many species of stinkbugs,

but in Kentucky soybeans they are usuallyrestricted to two groups -- the green and brownstinkbugs. (Note: there is a new species of brownstinkbug making its way across Kentucky. Thisspecies, the brown marmorated stinkbug, is also

likely to be a significant pest of soybeans, but thatis another story.)
http://news.utcrops.com/2013/06/kudzu-bugs-in-soybean/http://news.utcrops.com/2013/06/kudzu-bugs-in-soybean/http://news.utcrops.com/2013/06/kudzu-bugs-in-soybean/http://news.utcrops.com/2013/06/kudzu-bugs-in-soybean/http://news.utcrops.com/2013/06/kudzu-bugs-in-soybean/http://news.utcrops.com/2013/06/kudzu-bugs-in-soybean/


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Figure 3. Adult Kudzu bug on soybean leaf. Dr. Jeremy

Greene, Clemson University.

The adult Kudzu bugs are 1/6- 1/4 long, oblong,perhaps the size of an English pea; are olive-greencolored with brown speckles, and produce a mildly

offensive odor when disturbed. In the UnitedStates, characteristics of the adult kudzu buguseful in distinguishing it from other stinkbugs

include: the plate in the center of its back (calledthe scutellum) is broader along the rear than it is

along the head end, and much wider than it is long.The kudzu bug has a round body shape rather thanthe triangular to semi-elliptical body shape of our

native stinkbugs as well as a distinctive head

shape.

Figure 4. Kudzu bug eggs and nymphs. Dr. Philip Roberts,

University of Georgia.

Kudzu bug eggs are small and barrel shapedsimilar to stinkbug eggs, but are laid in a double

row laying on their side rather than sitting uprightin a cluster.

Nymphs are the immature forms that hatch from

the eggs. Their overall body shape is similar to theadult, but smaller, and they appear to be fuzzyor spiny while the adults are smooth.

Kudzu bug Facts

Though the kudzu plant aids in overwintering andis a reproductive host, our colleagues in the deepsouth have shown that the kudzu plant is NOT

required for kudzu bugs to establish. Soybean willdo just fine.

Kudzu bugs are infesting several soybeanfields in southeastern Tennessee.

Kudzu bugs are now established inAlabama and Mississippi.

Kudzu bugs are now in Virginia, but noton a direct interstate route to Kentucky.

Kudzu bugs are most detrimental to earlyplanted soybeans.

Current research in the Carolinas andGeorgia indicate that treatment is requiredwhen there is an average of 1 immature ortwo adults per sweep.

One of the biggest mistakes in kudzu bugcontrol is spraying too early, requiring a

second unnecessary spray.

Kentucky soybeans along the I-75, I-65and I-24 corridors are likely at the greatestrisk. These interstates bear traffic directly

from infested areas.

Kudzu bugs are also home invaders. Theywill try to get into structures during the

winter months.

The place to find all things kudzu bug is:

www.kudzubug.org
http://www.kudzubug.org/http://www.kudzubug.org/http://www.kudzubug.org/


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TOBACCO

Disease Update for the Week of July 8By Kenny Seebold, Extension Plant Pathologist

Current situation

Blue mold was apparently found on tobacco inLancaster, PA on or just before June 27. We haveyet to find blue mold in Kentucky, or any of theother tobacco-producing states south of Lancaster

so how the disease got into PA is a mystery.Given the location of the blue mold outbreak andour recent weather pattern, I think the chanceswere slim that the blue mold pathogen could havemoved from PA to KY or surrounding areas. We

should keep an eye out for the disease despite thelow risk and be ready to apply fungicides ifneeded.

Angular leaf spot (Fig. 5) has shown up on burley

tobacco in several parts of Kentucky, and wereseeing quite a bit more than we normally do. The

excessive amounts of rain that fell last weekcreated conditions that are favorable for the

development and spread of this disease. Likeother foliar diseases caused by bacteria, angularleaf spot can develop quickly during rainy

conditions, particularly when precipitation isheavy. The pathogen, Pseudomonas syringae pv.

angulata, is dispersed from foliar lesions readilyby rain splash, and heavy downpours can aid theentry of the pathogen into healthy leaves. The best

possible control for angular leaf spot is dryweather, which has been in short supply as of late.

In terms of chemical control, agriculturalstreptomycin (Ag Streptomycin or Agri-Mycin 17)can be applied as a foliar spray at a rate of 8 oz/50

gal of water per acre in fields where the disease isactive. Repeat applications can be made as

needed at 7-day intervals. The efficacy ofagricultural streptomycin against angular leaf spot

tends to be greater if treatments are made as soonas symptoms of disease are seen. Do not mixstreptomycin with Quadris, since we are not surethat leaf injury wont occur if these two are tank-mixed. Before a grower applies streptomycin forcontrol of angular leaf spot, make sure that the

problem has been diagnosed correctly. There arecertain environmental and nutritional issues that

can mimic, to some extent, the symptoms ofangular leaf spot. Treating with streptomycin in

these situations will do no good, and will cost theproducer in terms of time wasted and money

spent. Please let me know if you have anyquestions.

Figure 5. Symptoms of angular leaf spot on burley tobacco.Spots tend to be blocky, and bounded by leaf veins. A

chlorotic halo often surrounds the spots, which will appear

water-soaked initially will later take on a dark color.

Lesions can coalesce and form large, blighted areas on the

foliage, especially after heavy rain.

Tobacco Hornworm ControlBy Lee Townsend, Extension Entomologist

The second brood of tobacco hornworms can bevery destructive because eggs are laid over a longperiod of time so populations in a field may reachtreatable levels more than once. Field checks forhornworms provide the best chance to catch

potentially damaging infestations before they

cause significant yield loss and allow timing oftreatments before the worms are large enough to

reduce the effectiveness of the treatment.


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Hornworm infestations can be assessed bycarefully examining groups of 20 plants at

randomly selected locations over a field. Use aminimum of 5 locations per acre, add 2 stops for

each additional acre of field size. Eggs are laidsingly in the upper third of the plant and are

distributed relatively randomly over a field.Hornworms generally feed from the underside ofthe leaf so watch for damage and turn leaves over

to find live worms. Treat when there are 5 or morehealthy hornworms per 50 plants.

Many hornworms may have small, white, football-shaped objects on their backs. These are cocoons

of a tiny wasp that develops inside the hornwormand kills it. Hornworms with these cocoons should

not be included in your counts because they are nolonger feeding. Emerging wasps will attack other

caterpillars.

Two species, the tobacco hornworm and thetomato hornworm, occur in Kentucky. Thetobacco hornworm, the more common of the two,has 7 oblique white slashes on each side of the

body and a curved, red horn. The tomatohornworm has 8 V-shaped marks on each side anda straight, blue-black horn. The life cycle, damage,and activity period of both is so similar that, formanagement purposes, they can be lumped

together.

Figure 6. Tobacco hornworm.

Hornworms do the bulk of their feeding from the

time they are 1-1/2" long until they are full grown(about 4"). Try to apply treatments when mostcaterpillars are 2 long or less, this should result in

best control. Large worms are more difficult tocontrol.

Tobacco hornworm control options

Insecticide & Group Harvest Interval(days) +

comments

RestrictedEntry

Interval(hrs)

Bt products Agree,Biobit, DipelJavelin, Lepinox,XenTari

0 budworm,othercaterpillars.Most effectiveagainst small

caterpillars

4

Assail 30 SG or 70WP

Acetamiprid (4a)

7 also aphids,

budworms (eggstage), flea

beetles

12

Belt SC (28)

Flubendiamide

14 budworms,

othercaterpillars

12

Coragen SC (28)Chlorantraniliprole

1 budworm,othercaterpillars

4

Demin EC* (6)Emamectin benzoate

14 budwormand othercaterpillars

12

Tracer SCSpinosad (5)

3 budworms,other

caterpillars,

thrips

4

Voliam FlexiChlorantraniliprole +

Thiamethoxam

14 budworms,aphids, flea

beetles,Japanese beetles

12

* Restricted Use


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PESTS OF HUMANS

Potential Pest Problems Following ExtendedRainsBy Lee Townsend, Extension Entomologist

Several arthropods (and slugs) thrive and arrive

after prolonged rains. Expect an increase inaccidental invaders including, spiders, millipedes,

centipedes, and sowbugs or pillbugs that enterstructures in response to high water or extend thereare of activity because of humidity and dampness.

Also, there are midges, gnats, mosquitoes, andspringtails. These require moisture or high

humidity and can multiply rapidly following rains.A whole group of insects, including many beetles,

are associated with molds and fungi that increaseunder wet conditions.

Fortunately, most of these creatures are temporarynuisances that will disappear with drier conditions.

Until then, swatting, wiping, and collecting themwith a shop vac can be effective. Avoid thetemptation to over-apply insecticides; most are

temporary and problems will be resolved withsunshine and dry air.

Figure 7. Flat-backed millipede note 2 pairs of legs per

segment (Photo B. Jeffiers).

Millipedes can be temporary nuisances asaccidental invaders around houses near woods orwith naturalized areas around the foundation.

Large numbers of flat-backed millipedes,recognizable by the small side flanges extendinglaterally from each segment are typically activenow in Kentucky. However, they may range morewidely as a result of wet weather. Millipedes often

invade crawl spaces, damp basements, and ground

floors of houses. Common points of entry includedoor thresholds (especially at the base of slidingglass doors), expansion joints, and through thevoids of concrete block walls. Frequent sightings

of these pests indoors usually mean that there arelarge numbers have been breeding on the outside

in the lawn, or beneath mulch, leaf litter or debrisclose to the foundation. Because of their moisturerequirement, they do not survive indoors more

than a few days.

Figure 8. Midges and gnats.

Midges and gnats are common names for a largenumber of small, non-biting flies. Many species

look like mosquitoes and may form annoyingswarms or clouds in the air but they do not bite

and usually only live for a few days. Large matingswarms of adults often appear about dusk and mayoccur for several days, especially after a prolonged

wet period. Many gnats are attracted to light andmay be a nuisance, landing on people or enteringhomes or businesses. These tiny flies do not feed.

The immature stages develop in water in pools,

containers, ponds, and clogged rain gutters, alongwith mosquitoes. Some develop in wet soil andaccumulations of leaves and other matter. Most ofthe gnats feed on decaying plant matter, some livein very stagnant or polluted water. The adults only

live long enough to mate, lay eggs, and die. Eggsare laid in masses in the water or on aquaticvegetation. The life cycle usually takes about 4 to5 weeks. There may be several generations duringthe summer but these insects usually disappear

with the onset of dry weather.


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There are no good alternatives for control of theadults, other than some pressurized aerosol sprays

containing pyrethrins. These are impractical fortreating anything other than small areas. These

products only kill insects that are directly hit byspray particles, there is no lasting or residual

effect. More gnats will quickly enter the area afterthe spray has settled.

Long term control requires trying to eliminatebreeding sites, wet areas or standing water. Often,however, this is not practical. Water should not betreated with any insecticide in an attempt tocontrol gnats. The potential harm to the

environment and wildlife is too great to justify anapplication for a temporary nuisance.

Already there have been some problems with

springtails, small, wingless insects that are veryabundant in moist leaf litter or soils with highlevels of organic matter. They can hop around liketiny fleas. Springtails typically feed on decaying

plant material or fungi that grow in humid areas.They can enter homes from around the foundation

or openings to crawlspaces. In some cases,springtails can live for some time in damp areas ofhouses and buildings that meet their moistureneeds. These insects also can live in potscontaining over-watered houseplants. Allowing

the soil to dry out will usually eliminate them.

Occasionally, they can infest greenhouses wherethey may nibble on plant root hairs or tenderleaves.

Figure 9. Springtails.

Springtails are not harmful but their presence in anarea indicates moist conditions that may come

from things such as water leaks or condensationfrom sweaty pipes. Correcting these problems will

end the infestation and the potential for moreserious water or mold damage in a structure.

Using a fan or dehumidifier to increase ventilationand to provide a drying effect in the home can bevery effective as can repair of plumbing leaks and

dripping pipes. These actions will eliminate themoisture that springtails need for food andsurvival.

Aerosol insecticides that are labeled for indoor

insect control can be used to reduce springtailstemporarily but this does not correct the moisture

or humidity problems that allow the insects tothrive.

Outside the home, remove excessive mulch andmoist leaves, prune shrubbery and ground cover,and eliminate low, moist areas around the housefoundation to permit proper air circulation.Remove wet, moldy wood or other moldy items.

FUNGICIDES

Some Principles of Fungicide Resistance V:Ecological FitnessBy Paul Vincelli, Extension Plant Pathologist

Previous articles in this series have presented basicconcepts about how fungicide resistance developsin populations of infectious fungi. This article

presents a more advanced concept, but one that iskey to understanding fungicide resistance.

Ecologists use the term fitness to describe theoverall ability of an organism to thrive andreproduce in a given environment. Many qualitiescontribute to ecological fitness. An obvious

example is fungicide resistance. In a crop fieldwhere a fungicide is being used, if a spore hasgenetic resistance to that fungicide, it is more fitthan a spore that doesnt. Think of fungicideresistance like a coat of armor, protecting the

fungus from the fungicide (Figure 10).


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Figure 10. Imagine fungicide resistance being like a coat of

armor, protecting the spore from the chemical poison.

(Image of "ring armor", retrieved 23 June 2013, from

http://etc.usf.edu/clipart/).

Lets take the armor metaphor a little further.On the battlefield, having a coat of armor is

beneficial. However, in daily life, having to weara coat of armor would get tiresome very fast.

Sometimes, this is how it is with fungicideresistance. The genetic resistance to fungicideshelps protect the fungus for as long as the

fungicide is being used. However, if the producerstops using the fungicideor switches to a

fungicide in another FRAC group1the geneticresistance to fungicides actually may be a burden,

like an unnecessary coat of armor.

Here are some real-world examples:

When resistance develops to strobilurinfungicides (azoxystrobin, trifloxystrobin,

pyraclostrobin, and other FRAC Code 11fungicides), it commonly confers verylittle to no fitness cost. It is as if the armorwere weightless.

Resistance to the many triazoles andrelated fungicides (FRAC Code 3) often

1See thefourth articlein this series for a description of

FRAC groups.

results in a modest fitness cost, likewearing light-weight armor.

Resistance to dicarboximides (FRACCode 2) often comes at a significantfitness cost to the fungus, as if the armor it

was carrying was very heavy.

Although you may have never heard of ecological

fitness before, it really can work to a producersadvantage, or disadvantage. Imagine that a

fungicide-resistant spore occurs on your farm.Here is the range of possibilities:

If you are lucky, that genetic resistance tofungicides may have a fitness cost,

(=heavy armor). If so, that fungal strainmay limp along and cause disease on

your farm as long as you continue to usefungicides in that FRAC group. However,

if you stop using those fungicides, theresistant strain will commonly begin to dieout, and it may eventually return to very

low levels on your farm. If there is asubstantial fitness cost to fungicide

resistance, you can commonly go back tousing the fungicide, at least for awhile,until resistant strains build up again.

If you are unlucky, the resistant strain willhave absolutely no fitness cost, as if thecoat of armor weighed nothing at all.

What this usually means is, you are stuck

with resistance indefinitely. Even if youstop using fungicides in that particular

FRAC group, the resistant strain willpersist for a long time.

On a given farm, either of these two extremes mayoccur, as can outcomes intermediate between these

extremes.

So here are some practical questions that followfrom this concept of ecological fitness:

1. When fungicide resistance occurs,how fit are the resistant strains? Itis a key question, but it takes quite a

bit of research to answer it for anygiven case of resistance. It iscomplicated by the fact that each new

fungal strain, like people, is a uniqueindividual, and we will only knowhow well-adapted a strain is bywatching how it does in nature.
http://www2.ca.uky.edu/agcollege/plantpathology/extension/KPN%20Site%20Files/pdf/KPN%201346.pdfhttp://www2.ca.uky.edu/agcollege/plantpathology/extension/KPN%20Site%20Files/pdf/KPN%201346.pdfhttp://www2.ca.uky.edu/agcollege/plantpathology/extension/KPN%20Site%20Files/pdf/KPN%201346.pdfhttp://www2.ca.uky.edu/agcollege/plantpathology/extension/KPN%20Site%20Files/pdf/KPN%201346.pdf


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However, one thing is for sure: theoccurrence of resistance does not

necessarily pose a threat to a farmingoperation, depending on how fit the

resistant strain is.

2. How can we manipulate theecological fitness of pesticide-resistant microbes? Great question.But we cant. We have no influence

on whether or not the fungal spores ina particular field carry a heavy coat ofarmor or a weightless one. We canonly reduce the risk that the coat ofarmor will arise on its own (through

mutation). You can only hope that,once it arises, the coat of armor is

heavy. In ecological terms, we canonly reduce the chance that a fit

mutant will occur in our fields, but wecannot influence whether there is afitness cost to that resistance.

3. How can we reduce the chance of afit mutant occurring in our fields?The only way to reduce the risk of the

fit mutant is by reducing diseaseactivity on the farm. See thethird

articlein this series for more on thistopic, but basically, it means usingresistance varieties and cultural

practices to reduce disease pressure.

The lower the disease pressure, thelower the chance that a fit mutant willspontaneously occur.

Bottom line:Fungicide resistance is like a coat of armor,

protecting the fungus from the fungicide. In somecases, the coat of armor is heavy, becoming a

burden to the fungus in the absence of fungicide.This is referred to as a fitness cost to thefungicide resistance. If resistant strains in your

field carry a fitness cost, sometimes it is possible

to still use that fungicide selectively, because theresistant strain is may die out during periods whenthat fungicide is not applied. In contrast, if there isno fitness cost to resistance, resistant strains will

likely stick around for a long time.

Note: Trade names are used to simplify the information

presented in this newsletter. No endorsement by the

Cooperative Extension Service is intended, nor is

criticism implied of similar products that are not

named.
http://www2.ca.uky.edu/agcollege/plantpathology/extension/KPN%20Site%20Files/pdf/KPN%201344.pdfhttp://www2.ca.uky.edu/agcollege/plantpathology/extension/KPN%20Site%20Files/pdf/KPN%201344.pdfhttp://www2.ca.uky.edu/agcollege/plantpathology/extension/KPN%20Site%20Files/pdf/KPN%201344.pdfhttp://www2.ca.uky.edu/agcollege/plantpathology/extension/KPN%20Site%20Files/pdf/KPN%201344.pdfhttp://www2.ca.uky.edu/agcollege/plantpathology/extension/KPN%20Site%20Files/pdf/KPN%201344.pdfhttp://www2.ca.uky.edu/agcollege/plantpathology/extension/KPN%20Site%20Files/pdf/KPN%201344.pdf

Kentucky Pest News, July 9, 2013

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