kentucky pest news, august 20, 2013

7/27/2019 Kentucky Pest News, August 20, 2013

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Online at:www.uky.edu/KPN

Number 1353 August 20, 2013

GRAINS

- GMOs and Corn Mycotoxins- Watch for Soybean Aphids.

- Watch For Worms In Grain Sorghum Heads

TOBACCO

- Stink Bug Feeding on Tobacco

FRUIT- Consumption of Spotted Wing Drosophila

Infested Fruit

PESTS OF HUMANS

- Lone Star Larvae (Seed Ticks and Turkey Mites)Give Unpleasant Experiences

DIAGNOSTIC LAB HIGHLIGHTS

INSECT TRAP COUNTS

GRAINS

GMOs and Corn Mycotoxins

Paul Vincelli, Extension Plant Pathologist

Corn is a staple crop for human food and livestockfeed. Like a number of other crops, corn grain can

be naturally contaminated by mycotoxins, natural

toxins produced by fungi. The classes ofmycotoxins of most likely to cause concern in

Kentucky are fumonisins and aflatoxins.

Though most Kentucky corn crops are free ofmycotoxins,fumonisinsare probably the mostcommon threat (Figure 1). These toxins affect a

number of animal species, but horses and pigs areamong the most sensitive.Aflatoxinsare generally

very uncommon in Kentucky, but when theyoccur, they can cause serious disruption to grainmarketing. Both mycotoxin families pose health

risks to humans. More information can be foundin the two University of Kentucky Extension

publications listed under my name in thebibliography below.

Figure 1.

Fusarium ear

rot of corn,

usually

associated

with fumonisin

contamination

Wounding of the corn kernel (Figure 2) makes iteasier for the kernels to become infected by the

fungi that produce these mycotoxins. Europeancorn borer and other caterpillars commonly

produce wounds that favor infection andmycotoxin contamination. That being the case,does the use of genetically modified Bt corngenetically engineered to provide control ofcertain insect pestsresult in reduced mycotoxin

contamination?

To address this question, field studies have beenconducted comparing Bt-hybrids to non-Bthybrids that are otherwise genetically very similar.

Thus far, the overall results fr om this li ne of

research are that meaningfu l mycotoxin

reductions sometimes occur due to the Bt trait.Since (to my knowledge) there is no significant

Lexington, KY 40546
http://www.uky.edu/KPNhttp://www.uky.edu/KPNhttp://www.uky.edu/KPNhttp://ww.ca.uky.edu/agc/pubs/id/id121/id121.pdfhttp://ww.ca.uky.edu/agc/pubs/id/id121/id121.pdfhttp://ww.ca.uky.edu/agc/pubs/id/id121/id121.pdfhttp://www2.ca.uky.edu/agc/pubs/id/id59/id59.pdfhttp://www2.ca.uky.edu/agc/pubs/id/id59/id59.pdfhttp://www2.ca.uky.edu/agc/pubs/id/id59/id59.pdfhttp://www2.ca.uky.edu/agc/pubs/id/id59/id59.pdfhttp://ww.ca.uky.edu/agc/pubs/id/id121/id121.pdfhttp://www.uky.edu/KPN


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body of peer-reviewed research indicating a food-safety risk from Bt corn, the appropriate use of Bt

corn is widely considered to be potentiallybeneficial both for animal health as well as forsafety for human consumption. A more detaileddiscussion follows.

Figure 2. Aspergillus ear and kernel rot of corn, often

associated with aflatoxin contamination. The fuzzy

appearance inside the kernel is the sporulation of theinvading fungus.

Fumonisins

Fusarium ear and kernel rot is a disease oftenassociated with fumonisin contamination, and field

studies have shown reduced Fusarium ear rot fromBt corn. Not surprisingly, these reductions have

been tied to reductions in insect feeding on kernelscontaining the Bt toxin. Studies in the USA andEurope have also shown that Bt hybrids often

produce corn with reduced fumonisin content

with these reductions also being tied to reductionsin insect feeding on Bt kernels. In studies wherestatistically significant reductions in fumonisinconcentration occurred, these ranged from 20% toover 90%, often bringing the grain belowconcentrationsthought to pose risks to humans

and the most sensitive animals. It is interesting tonote that the application of synthetic insecticidesto control kernel-feeding insects on non-Bt plantsalso sometimes reduces insect feeding andfumonisin contamination. This opens the door to

an interesting discussion as to which is moresustainable: use of the Bt trait or application ofinsecticides. Either way, reductions in fumonisin

contamination are highly desirable.

AflatoxinsAs with fumonisins, field studies have oftendocumented reductions in aflatoxin contamination

due to the Bt trait. Significant reductions weremost common when aflatoxin levels were atmoderate to high levels in the non-Bt corn. Instudies where significant reductions in

contamination were documented, these commonlyranged from 50 to 90%. In some cases, the

reductions in aflatoxin concentration from the Bttrait were sufficient to bring the corn below 20

parts per billion, an important regulatory thresholdfor use of the grain in human foods. As with

fumonisins, aflatoxin reductions have generallybeen linked to reductions in kernel injury frominsect feeding. In cases where the Bt trait did notresult in aflatoxin reductions, other factorsespecially drought stressmay have been moreimportant in promoting aflatoxin accumulation

than insect damage to kernels.

CaveatsThere are several caveats and complicating factors

in this line of research, as follows:

Bt corn isnt a magic bullet, eliminating allmycotoxin contamination. Indeed, sometimesreductions in mycotoxin contamination do not

occur. This is true for both fumonisins and foraflatoxins. However, reductions of fumonisinsand aflatoxins have been documentedcommonly in field studies, especially underconditions moderately to highly favorable for

ear rot and mycotoxin contamination. Suchreductions occur commonly enoughwith noknown downsides relating to consumptionof the grainthat the appropriate use of Btcorn is considered to be beneficial both for

food safety as well as for animal health. The Bt toxin must be expressed in the corn

kernel in order to reduce these mycotoxins, byreducing insect injury. In some Bt cornhybrids, the Bt toxin is not expressed in thekernel. Such hybrids have no protection

against wounds created by insect feeding, andtherefore fumonisin contamination is not

reduced in these hybrids.

While the Bt trait is important in reducingmycotoxin contamination, the magnitude ofmycotoxin reduction can depend on the

genetic background of the corn hybrid. Inother words, if you compare two hybrids that

have the identical Bt trait, one may have lessfumonisin than the other, simply because of itsgenetic background.

The effectiveness of the Bt trait in reducingmycotoxin contamination depends on theinsect pest present. For example, Bt corn is

often effective at reducing feeding damagefrom the European corn borer, but not the corn
http://www2.ca.uky.edu/agc/pubs/id/id121/id121.pdfhttp://www2.ca.uky.edu/agc/pubs/id/id121/id121.pdfhttp://www2.ca.uky.edu/agc/pubs/id/id121/id121.pdf


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earworm. Consequently, reductions infumonisin contamination may occur if the

European corn borer is the principal pest in afield, but not if the corn earworm is

predominant.

Bottom lineCorn hybrids that express the Bt trait in kernelssometimes exhibit reduced kernel contaminationfrom fumonisins and aflatoxins. This is thought to

be due to reduced insect feeding on the kernels.The Bt trait is not a silver bullet, eliminating all

mycotoxin risk. However, reductions occurcommonly enough, with no known downside,that the Bt trait is commonly thought to contributeto food safety and livestock health in both

developed and developing countries. While it iswell-documented that the Bt trait can reduce

mycotoxin contamination, it is best used wisely,and only in fields with a moderate to high risk ofdamage from the target insect pests.

AcknowledgmentThanks to Charles Woloshuk (Purdue University)

and to Ric Bessin (University of Kentucky) forreviewing a draft of this article.

Relevant Scientific Papers

Clements, M. J. et al, 2003. Influence ofCry1Ab protein and hybrid genotype on

fumonisin contamination and Fusarium ear rotof corn. Crop Science 43:12831293.

Dowd, P. F. 2000. Indirect reduction of earmolds and associated mycotoxins inBacillusthuringiensis corn under controlled and openfield conditions: Utility and limitations.

Journal of Economic Entomology 93:1669-1679.

Folcher, L., et al, 2009. Comparative activityof agrochemical treatments on mycotoxinlevels with regard to corn borers and Fusariummycoflora in maize (Zea mays L.) fields. Crop

Protection 28:302308. Folcher, L. et al, 2010. Lower mycotoxin

levels in Bt maize grain.Agronomy for

Sustainable Development30:711719

Munkvold, G. P., Hellmich, R. L., andShowers, W. B. 1997. Reduced Fusarium earrot and symptomless infection in kernels ofmaize genetically engineered for Europeancorn borer resistance.Phytopathology

87:1071-1077.

Munkvold, G.P. and Hellmich, R.L. 1999.Genetically modified insect resistant corn:Implications for disease management.APSnet

Features. Online. doi:10.1094/APSnetFeature-1999-1199

Munkvold, G. P., Hellmich, R. L., and Rice,L. G. 1999. Comparison of fumonisinconcentrations in kernels of transgenic Btmaize hybrids and nontransgenic hybrids.

Plant Disease 83:130-138.

Vincelli, P. and Parker, G. 2002.Fumonisin,Vomitoxin, and Other Mycotoxins in Corn

Produced by Fusarium Fungi.http://www2.ca.uky.edu/agc/pubs/id/id121/id121.pdf

Vincelli, P., Parker, G., and McNeill, S., 2002.Aflatoxins in Corn.http://www2.ca.uky.edu/agc/pubs/id/id59/id59

.pdf

Williams, W. P. et al, 2002. Aflatoxinaccumulation in conventional and transgeniccorn hybrids infested with southwestern corn

borer (Lepidoptera: Crambidae).Journal ofAgricultural and Urban Entomology 19:227-

236.

Williams, W. P. et al, 2005. Southwesterncorn borer damage and aflatoxin accumulationin conventional and transgenic corn hybrids.

Field Crops Research 91:329336.

Watch for Soybean Aphids

Doug Johnson, Extension Entomologist

Soybean aphid (Figure 3) has been found in

Kentucky since its introduction into the U.S.Nevertheless, it has not developed into a pest

species for Kentucky-grown soybeans. This isattributed largely to two factors: 1.) We do nothave the plant host for the overwintering stage,

meaning the aphid must migrate annually intoKentucky from more northern states and 2.)

Soybean aphid populations do not do well in thehot temperatures of a Kentucky July and August.So, in a typical year this pest does not pose muchof a risk.

The spring and summer of 2013, however, havebeen anything but the typical Kentucky weather. Ithas been wetter, and perhaps more importantly,cooler than our average year. In addition, this has

been true of states to the north of KY. For
http://www2.ca.uky.edu/agc/pubs/id/id121/id121.pdfhttp://www2.ca.uky.edu/agc/pubs/id/id121/id121.pdfhttp://www2.ca.uky.edu/agc/pubs/id/id121/id121.pdfhttp://www2.ca.uky.edu/agc/pubs/id/id59/id59.pdfhttp://www2.ca.uky.edu/agc/pubs/id/id59/id59.pdfhttp://www2.ca.uky.edu/agc/pubs/id/id59/id59.pdfhttp://www2.ca.uky.edu/agc/pubs/id/id59/id59.pdfhttp://www2.ca.uky.edu/agc/pubs/id/id59/id59.pdfhttp://www2.ca.uky.edu/agc/pubs/id/id121/id121.pdfhttp://www2.ca.uky.edu/agc/pubs/id/id121/id121.pdf


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example, my colleagues in Ohio, Iowa, Indiana,and Illinois, among others, have reported rising

and, in some cases, economic populations in somesoybean fields. Dr. Mike Grey at the University ofIllinois is encouraging Illinois producers to scoutfor soybean aphid populations over the next

several weeks.

Figure 3. Soybean aphid on soybean.

I doubt that this is a major outbreak for Kentucky.Even so, with the cool weather we have

experienced, the large amount of late-plantedsoybeans, and the increased activity to our north, I

believe it is prudent to pay more attention to thispest than we have in the past.

Soybean aphids are small, pale to bright yellow,soft bodied, pear shaped insects. Aphids have a

pair of black cornicles (tail pipe lookingstructures) sticking out the rear end. You may seesome small white aphids; this is just a colorvariation. You might see the occasional singlecotton/melon aphid, but soybean aphid is the only

aphid that colonizes soybeans in the U.S.

The economic threshold for soybean aphid has notchanged. It is: 250 aphids per plant, with 80% of

plants infested, and an increasing population (this

means at least two measures must be taken overtime). Direct plant observation is the best method

of detecting the soybean aphid and it gives a goodmeasure of population growth. Unfortunately, it isvery time consuming. Using the Speed Scoutingmethod may be better for making a controldecision. This is a relatively quick and physically

easier method of decision making, but does notgive quite the picture of how the population is

growing / declining. You may obtain a copy of theSpeed Scouting form at:

http://www.soybeans.umn.edu/crop/insects/aphid/aphid_sampling.htm

On this Web page, look toward the upper right

hand side under Resources for the 2007 SpeedScouting Worksheet. You can download this andmake copies for use in the field.

Should it become necessary, pesticides for controlof soybean aphid may be found in ENT-13

Insecticide Recommendations for Soybeans. Thisis available at:http://pest.ca.uky.edu/EXT/Recs/welcomerecs.htmlor you may get a copy from your local County

Extension Office.

Heres hoping no one finds an aphid!

Watch for Worms in Grain Sorghum Heads

Doug Johnson, Extension Entomologist

It is about the time of year for problems with corn

earworm (Figure 4.) to begin in grain sorghum.Though I have not seen or heard of any local

problems, my colleague in Virginia, Dr. AmesHerbert, is beginning to see some problems. InKentucky we generally see these problems in the

area west of the Pennyrile Parkway and moreimportantly in LATE-planted fields. You are also

likely to see a mixture of worm species includingthe sorghum webworm (Figure 5).

Figure 4. Corn

earworm in corn.

(Photo: Cam

Kenimer)
http://www.soybeans.umn.edu/crop/insects/aphid/aphid_sampling.htmhttp://www.soybeans.umn.edu/crop/insects/aphid/aphid_sampling.htmhttp://pest.ca.uky.edu/EXT/Recs/welcomerecs.htmlhttp://pest.ca.uky.edu/EXT/Recs/welcomerecs.htmlhttp://pest.ca.uky.edu/EXT/Recs/welcomerecs.htmlhttp://pest.ca.uky.edu/EXT/Recs/welcomerecs.htmlhttp://pest.ca.uky.edu/EXT/Recs/welcomerecs.htmlhttp://www.soybeans.umn.edu/crop/insects/aphid/aphid_sampling.htmhttp://www.soybeans.umn.edu/crop/insects/aphid/aphid_sampling.htm


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Figure 5. Sorghum

webworm on sorghum.

(Photo: Alton N. Sparks,

Jr., Bugwood.org)

You should begin sampling any sorghum fieldsthat have heads entering the milk stage. Using the

bucket/shake method is the best way to determine

the average number of worms per head. Irecommend doing a series of 10-head samples ineach field. At each location shake 10 randomlyselected heads into a white 5-gallon bucket, countthe worms and divide by 10. This will give the

average number of worms per head at thatlocation. You should do this for at least fivelocations in each field; then add the averagenumber of worms at each location and divide that

by the number of locations sampled. This will give

you an overall average number of worms per head

for the field. Recommendations are pretty variableacross states, but an average of 2 worms per head,

or more, is a pretty common trigger for a spray.

If treatment is needed use a sprayboom/nozzle/gpa/psi system that delivers as much

product to the heads as possible. Remember theheads are not a flat surface, so this is much morelike covering a wheat head with a fungicide asopposed to a replant herbicide application. Thehead has structure and shape and needs to be

completely covered. Spraying leaves is a waste of

time and product the product hitting the heads, thebetter. Directing sprays to the heads is even more

important in varieties with compact heads (vs.loose heads). When heads are compact, worms

tend to burrow to the center, are not easily seen,and are not as vulnerable to sprays. Remember, theinsecticides used for worm control depend on

direct contact.

What insecticides should you use? Sorghum hasfewer labeled insecticides than many commodities,

but there is a pretty good selection with differentmodes-of-action. Pyrethroids include Tombstone,Mustang Maxx, Warrior, and Asana XL, andothers. Non-pyrethroids include Belt, Blackhawk

(was Tracer), and Lannate. There are a few othersthat combine active ingredients like Stallion(Mustang + Lorsban) and Consero (Prolex +Tracer). Note that I have not evaluated these

products so cannot make comments about control,but colleagues in other states have experienced

lack of control with pyrethroids, alone, whenworm populations were high or worms were alarge size (harder to kill) when sprays wereapplied.

TOBACCO

Stink Bug Feeding on Tobacco

Lee Townsend, Extension Entomologist

Yellow, brown, or wilted leaves on tobacco plants

(Figure 6) may be a sign of feeding by brown stinkbugs. These 1/2" long sap-feeding insects injectenzymes that can cause leaf tissue to wilt orcollapse.

Figure 6. Wilted, yellow leaf due to stink bug feeding

Weather affects the severity of the plant response.

At first, stink bug feeding causes a leaf to wiltquickly and turn a darker shade of green. Onovercast days, these leaves often recover and grownormally. However, hot sunny conditions cancause the entire leaf to scald, then over the next

few days turn brown and die. Injured plants often


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are most common along field margins but if stinkbugs are abundant, they can be scattered over the

field.

The damage usually is not obvious for severaldays so the bugs often have left the field. Stink

bugs are good fliers and move frequently fromplant to plant as well as into and out of the field.Because of their movement and generally minimaldamage, insecticide applications are rarely

justified.

FRUIT

Consumption of Spotted Wing Drosophila

Infested Fruit

Ric Bessin, Extension Entomologist

I have received several phone calls from extensionagents regarding homeowners inquiring aboutspotted wing Drosophila (SWD) infesting theirsmall-fruit crops (Figure 7) and the safety ofeating the infested fruit. First let me state that Im

not a fan of eating insects, dead or alive. Fromwhat Ive read, while Drosophila larvae dontdirectly attack humans, ingesting the larvae has

been reported to cause intestinal discomfort andeven diarrhea. Dropsohila damaged and infested

produce is also more likely to contain other

microbe contaminants as well. To make aninformed decision, I think it would be good tosample the fruit presence of SWD larvae.

Figure 7. Spotted wing Drosophila on grape.

Floatation MethodTo sample fruit for SWD it is important to sample

only sound, undamaged fruit. Damaged, overripeor rotting fruit are likely to contain other types offlies besides SWD. You will need to have about adozen to two dozen fruit that appear undamaged.

Place the fruit into a sealable plastic bag and crushthe fruit. Into the bag add 2 cups of a sugar-watersolution (2 cups water plus cup sugar). Seal the

bag and mix the contents thoroughly then let thecontents settle. SWD larvae will appear lightcolored and inch or less in length. The body

tapers a bit at both ends.

Small fruit suitable for eating should beimmediately refrigerated, as the fruit may contains

SWD eggs under the skin of the berries. Placingthe berries in a cooler or refrigerator will arrest the

development of the eggs and any larvae. This willalso help to maintain the quality of the fruit andreduce deterioration if small larvae are present.

PESTS OF HUMANS

Lone Star Larvae (Seed Ticks and Turkey

Mites) Give Unpleasant Experiences

Lee Townsend, Extension Entomologist

Outdoor activity can bring people into contact

with large clusters of hungry lone star tick larvae(Figure 8) that also are called seed ticks and turkeymites. The tiny six-legged larvae are about the sizeof a freckle when they hatch. They are hungry so

they climb short vegetation, especially grass, to sitwith out-stretched front legs to latch on to a

passing animal or person.

Figure 8.

Newly hatched

lone star tick

larvae.

On humans, seed ticks will settle where clothing istight against the skin or in folds behind knees, etc.

and insert their long mouthparts to feed. Once


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settled, they cement themselves in place andengorge on blood. The saliva injected as they feed

can cause intense itching at the bite site that willcontinue for a week or longer after the tick isremoved or drops off.

Here are some tips to reduce problems with ticks: Check yourself regularly; ticks wander on

people for a long time before settling to feed.

When removing ticks, use fine-tippedtweezers or protect your fingers from directtick contact with a tissue, paper towel, orrubber gloves.

Grasp the tick as close to the skin surface aspossible and pull upward with steady, even

pressure. Don't twist or jerk it; this action maycause the mouthparts to break off and remain

in the skin. (If this happens, remove

mouthparts with tweezers. Consult yourhealthcare provider if infection occurs.)

Wash the area with soap and water. Do not squeeze, crush, or puncture the body of

the tick because its fluids (saliva, hemolymph,gut contents) may contain infectious

organisms.

DIAGNOSTIC LAB HIGHLIGHTS

Julie Beale and Brenda Kennedy, Plant DiseaseDiagnosticians

Agronomic samples diagnosed in the Plant

Disease Diagnostic Lab in the past week haveincluded crown rots (Rhizoctonia sp.,Phoma

sp.) and summer black stem & leaf spot on

alfalfa; common and southern rusts on corn;stem canker, Phytophthora root rot, sudden

death syndrome, and downy mildew on

soybean; frogeye leaf spot, potyvirus complex,and frenching on tobacco.

On fruit and vegetable samples, we have

diagnosed black rot and Phomopsis cane &leaf spot on grape; Phytophthora root rot and

Botryosphaeria canker on blueberry; brown

rot on peach and nectarine; anthracnose (foliarlesions) on apple; Cercospora leaf spot and

gummy stem blight on cantaloupe; downy

mildew on pumpkin; early blight, Septoria leaf

spot, Phoma leaf spot, late blight, Fusarium

wilt, ripe rot, russet mite injury, and tomato

spotted wilt virus on tomato; and gummy stemblight on watermelon.

On ornamentals and turf, we have seenPythium root rot on chrysanthemum; powderymildew and leaf blotch on peony; rosette on

rose; fungal twig blights on arborvitae; leaf

rust on cottonwood; Botryosphaeria canker onmaple; tip blight on pine; Cylindrosporium

leaf spot on walnut; Pythium root dysfunction

on bentgrass; and large patch on

bermudagrass.

2013 INSECT TRAP COUNTS

August 9 to August 16

Graphs of insect trap counts for the 2013 seasonare available on the IPM Web site at -http://www.uky.edu/Ag/IPM/ipm.htm.

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.

Location Princeton, KY Lexington, KY

Black cutworm 4 3

Armyworm 0 35

European corn

borer

0 3

Corn earworm 52 16

Southwestern corn

borer

22 0

Fall armyworm 6 0
http://www.uky.edu/Ag/IPM/ipm.htm.http://www.uky.edu/Ag/IPM/ipm.htm.http://www.uky.edu/Ag/IPM/ipm.htm.

kentucky pest news, august 20, 2013

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