kentucky pest news, october 26, 2010

8/8/2019 Kentucky Pest News, October 26, 2010

1/9

Online at:www.uky.edu/KPN

Number 1251 October 26, 2010

CORN

-Sampling Corn Fields in Autumn for

Nematodes

-Aflatoxins

VEGETABLES

-Managing Stink Bugs on Fruiting Vegetables

CORN

Sampling Corn Fields in autumn for

NematodesBy Paul Vincelli

Nematodes are microscopic roundworms that

attack roots of corn and other plants (Fig 1.). In

corn, nematodes affect yield by damaging theroot system. They become more important

when there are other root-related stresses in the

same field, such as moisture shortage, root

damage from insects, or compaction.

There is increasing interest in nematodes that

attack corn, for several reasons:

1. In the past, soil-directedorganophosphate and carbamateinsecticides gave some secondary

suppression of nematodes. Currently,

more selective insecticides, and Bt corn

for corn rootworm control, dont

provide secondary suppression ofnematodes.

2. The increase of no-till production canfavor certain nematodes that aresensitive to tillage (needle and dagger

nematodes).

3. More corn-following-corn also favorsthe needle and dagger nematodes.

HOUSEHOLD

-Brown Marmorated Stink Bug Look-A-Likes in

Kentucky

NUT CROPS

-Walnut Bunch Disease

Although there is increasing interest innematodes as potential yield-limiting factors, the

threat these pose varies greatly from one field to

the next. The best way to determine whether

nematodes may be affecting yield is to samplefor nematodes. While winter temperatures will

cause some nematode mortality, sampling in the

autumn after crop maturity gives a producer timeto react to findings, by obtaining seed treated

with Avicta seed treatment or considering analternative crop.

For sampling in the autumn, use a soil probe and

sample within the rowthats right, within the

row. This is different from sampling for soil

fertility. Sampling within the row allows you to

Lexington, KY 40546

Figure 1. "Head" of nematode,

showing the spear-like stylet (arrow)

that it uses to puncture plant cells.
http://www.uky.edu/KPNhttp://www.uky.edu/KPNhttp://www.uky.edu/KPNhttp://www.uky.edu/KPN


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get a count of destructive endoparasitic

nematodes (lesion and lance nematodes),

because many of those adults leave the root as

the crop dries down and the roots die. Sample

when the soil is moist but not wet. Walk a zig-zag pattern, and take 20 cores to a depth of 12

inches. Gently mix these cores in a container.Dont let them dry out or be subjected to

temperature extremes before mailing as soon as

feasible to a nematode laboratory.

Laboratories that can analyze nematodes in soilsamples collected at this time of year include:

Purdue University,http://extension.entm.purdue.edu/nemat

ology/cv/submissionform.pdf

Mississippi State University,http://msucares.com/pubs/misc/m1230.p

df

University of Florida,http://edis.ifas.ufl.edu/sr011

Iowa State University,http://www.extension.iastate.edu/Public

ations/PD32.pdf

AflatoxinsBy Paul Vincelli, Extension Plant Pathologist

and Sam McNeill, Extension Agricultural

Engineer

Aflatoxins are showing up in occasional lots of

harvested corn from this seasons crop.Aflatoxins metabolites of the fungusAspergillus

flavus, are potent toxins and carcinogens in

animals, and may also be human carcinogens.

Aflatoxins are probably the most well-known

mycotoxins, because they have long been

regulated by the US Food and Drug

Administration.

During grain fill, many Kentucky corn fields

experienced high temperatures (highs above

90F, with warm nights) and drought conditions,

which favorAspergillus infection and aflatoxincontamination of the kernels. Kernel injury

caused by insects, mechanical damage during

harvest or handling, or other causes can lead to

an increase in aflatoxin levels (Figure 3), though

infection and contamination can occur even in

undamaged kernels if conditions are highly

favorable for the fungus.

Grain Storage

Mycotoxins such as aflatoxin can accumulate incorn in storage. Table 1 below providesrecommended conditions that will suppress mold

growth in storage. Corn with evidence of mold

or mechanical damage or excess trash should be

held at 0.5 to 1% lower moisture content thanrecommended here. Monitor stored corn

regularly for mustiness and grain heating.

Figure 2. Range of populations of lance nematode in 33

Kentucky corn fields sampled in 2009.

Figure 3. Yellow-brown sporulation ofAspergillus

flavus in an insect-injured corn kernel.
http://extension.entm.purdue.edu/nematology/cv/submissionform.pdfhttp://extension.entm.purdue.edu/nematology/cv/submissionform.pdfhttp://extension.entm.purdue.edu/nematology/cv/submissionform.pdfhttp://msucares.com/pubs/misc/m1230.pdfhttp://msucares.com/pubs/misc/m1230.pdfhttp://msucares.com/pubs/misc/m1230.pdfhttp://edis.ifas.ufl.edu/sr011http://edis.ifas.ufl.edu/sr011http://www.extension.iastate.edu/Publications/PD32.pdfhttp://www.extension.iastate.edu/Publications/PD32.pdfhttp://www.extension.iastate.edu/Publications/PD32.pdfhttp://www.extension.iastate.edu/Publications/PD32.pdfhttp://www.extension.iastate.edu/Publications/PD32.pdfhttp://edis.ifas.ufl.edu/sr011http://msucares.com/pubs/misc/m1230.pdfhttp://msucares.com/pubs/misc/m1230.pdfhttp://extension.entm.purdue.edu/nematology/cv/submissionform.pdfhttp://extension.entm.purdue.edu/nematology/cv/submissionform.pdf


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Table 1. Recommended Grain Temperatures for

Storage in Western Kentucky.*

Target

Average Target grain

Month air temp. grain temp. moisture

Sept 70F 60 - 70F 14.0%

Oct 60F 55 - 60F 15.0%

Nov 47F 42 - 52F 15.0%

Dec- 37F 32 - 42F 15.0%Feb

March 47F 42 - 52F 14.0%

April 55F 50 - 60F 13.0%*See AEN-45 "Aeration, Inspection, and

Sampling of Grain in Storage."

Permissible levels

Aflatoxins are regulated at theparts-per-billionlevel, an extremely low level. To put this in

perspective, one part-per-billion is equivalent to

one second in 32 years, or one kernel in a 10,000

bushel bin.

For many uses, grain must have less than 20

parts-per-billion (ppb) of aflatoxin. However,

there are some permissible uses for corn with

higher levels. For example, mature cattle can be

fed corn with up to 300 ppb aflatoxin. Detailson the permissible levels of aflatoxins in

livestock feeds and human foods are available in

the UK Extension publication,Aflatoxins in

Corn, ID-59,

http://www.ca.uky.edu/agc/pubs/id/id59/id59.pd

f.

Blacklight testing

Examining the kernels for yellow-green

fluorescence under a blacklight is commonlyused as a quick preliminary test. The entire

sample should be cracked or coarse-ground for

blacklight testing. However, yellow-green

fluorescence under a blacklight does not indicate

the presence of aflatoxins. Fluorescence simply

indicates that aflatoxins may be presentin thekernel. A blacklight test can often give a "false

positive"; that is, a positive result from a clean

load of corn. A similar glow under blacklight

may be produced by tips of corn kernels, corn

beeswings (glumes), soybean hulls, certain weed

seeds, and strains ofA. flavus that do not

produce aflatoxins. Plus, it is also possible to

get a negative blacklight result from a

contaminated sample. Thus, blacklight testing is

not considered to be a reliable method for

detecting aflatoxin.

Sampling Corn for Testing

Aflatoxin testing is notoriously variable.Sampling for any contaminant in grains at the

parts-per-billion level is highly variable. See

Table 2 below for an illustration of this

variability.

Table 2. Aflatoxin test results (parts-per-billion,

ppb) in ten properly collected samples obtained

each of three peanut lots (arranged in ascending

order for ease of interpretation).

One cant prevent this sort of variability whentesting for aflatoxin, but one can make it worse

by not sampling correctly. The recommended

sampling procedure for corn is as follows: Take

at least ten probefuls and collect at least 10 lb of

corn. The corn must be below 16% moisture

unless the test is being performed immediately.

Test results from high-moisture corn may not be

accurate if the test is delayed, as the fungus can

continue to grow and produce aflatoxins. The

10-lb sample must be ground and mixed well

before drawing a small subsample for testing.

The AOAC International (formerly theAssociation of Official Analytical Chemists)

requires that the entire 10-lb sample be coarsely

ground to pass through a No. 14 sieve and

mixed, and that a 2- to 4-lb subsample be ground

to pass through a No. 20 sieve (about the

consistency of fine instant coffee), before

aflatoxin testing.
http://www.ca.uky.edu/agc/pubs/id/id59/id59.pdfhttp://www.ca.uky.edu/agc/pubs/id/id59/id59.pdfhttp://www.ca.uky.edu/agc/pubs/id/id59/id59.pdfhttp://www.ca.uky.edu/agc/pubs/id/id59/id59.pdfhttp://www.ca.uky.edu/agc/pubs/id/id59/id59.pdf


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Test kits are available from several

manufacturers. Some of these test only for the

presence or absence of aflatoxins. Other, more

sophisticated kits estimate the concentration of

aflatoxin. If using one of these, grain should beground and mixed as described above, and

operators should be well-trained in the use of theparticular test kit being employed.

Analytical laboratories provide the bestestimates of aflatoxin concentration. Drawbacks

of laboratory testing include expense and time

delays while waiting for results.

Management for 2011

Stored corn should be managed as described

above, so as not to allow aflatoxin accumulation

in storage. As far as planning for the 2011 crop,

any fields with aflatoxin this year have only avery, very modest increase in aflatoxin risk next

year. Of course, most of those will be rotated as

normal, and aflatoxin is only a concern in corn.

Even for those that are sown to corn in 2011,

aflatoxin contamination is driven much more by

environmental conditions than by cropping

history and agronomic practices. Of course,

since aflatoxin contamination is commonly

associated with drought and grain damage, it is

advisable to use good agronomic practices such

as: sowing adapted hybrids, avoiding excessive

plant populations, reducing soil compaction (ifpresent), and managing kernel-feeding insects.

Additional Resources

Details on many aspects of aflatoxins are

available in the UK Extension publication,

Aflatoxins in Corn, ID-59,

http://www.ca.uky.edu/agc/pubs/id/id59/id59.pd

f

Grain storage recommendations are available in

the UK Extension publication,A Comprehensive

Guide to Corn Management in Kentucky, ID-139,

http://www.ca.uky.edu/agc/pubs/id/id139/id139.

pdf

A multi-state Extension publication entitled

Moldy Grains, Mycotoxins, and Feeding

Problems is available at

http://www.oardc.ohiostate.edu/ohiofieldcropdisease/Mycotoxins/mycopagedefault.htm

VEGETABLES

Managing Stink Bugs on Fruiting VegetablesBy Ric Bessin

Stink bugs can be elusive and difficult insects to

manage on some vegetables crops. They are

elusive in that it is often the damage that is firstnoticed rather than the stink bugs themselves.

They can be difficult to control as they tolerate

of some commonly used insecticides and their

mobility allows them to re-infest treated fieldsafter treatment. Stink bugs feed with piercing-sucking mouthparts which cause whitish-yellow

corky spots underneath the skin of the fruit.

These are often referred to as cloud spots on

the fruit. The feeding may occur a week or more

before the damage becomes pronounced.

Initially the damage may appear as lighter spots

with a dark point in the center. This damage can

result in serious losses for peppers, tomatoes,

and eggplant as it can render the fruit

unmarketable.

There are three species of brown stink bugs that

currently are our most damaging stink bug pests

of fruiting vegetables. These are the brown stink

bug (Euschistus servus), the one-spotted stink

bug (Euschistus variolarius), andEuschistus

tristigmus. They differ in size ranging from 3/8

of an inch withE. tristigmus to inch for the

two other species. While identification to species

can be difficult, the damage they cause is very

similar and they can be treated as a brown stink

bug complex. Nymphs of these species look

similar and are small than the adults withexternal wing buds. Each of these species has

five nymphal stages.
http://www.ca.uky.edu/agc/pubs/id/id59/id59.pdfhttp://www.ca.uky.edu/agc/pubs/id/id59/id59.pdfhttp://www.ca.uky.edu/agc/pubs/id/id59/id59.pdfhttp://www.ca.uky.edu/agc/pubs/id/id139/id139.pdfhttp://www.ca.uky.edu/agc/pubs/id/id139/id139.pdfhttp://www.ca.uky.edu/agc/pubs/id/id139/id139.pdfhttp://www.oardc.ohiostate.edu/ohiofieldcropdisease/Mycotoxins/mycopagedefault.htmhttp://www.oardc.ohiostate.edu/ohiofieldcropdisease/Mycotoxins/mycopagedefault.htmhttp://www.oardc.ohiostate.edu/ohiofieldcropdisease/Mycotoxins/mycopagedefault.htmhttp://www.oardc.ohiostate.edu/ohiofieldcropdisease/Mycotoxins/mycopagedefault.htmhttp://www.oardc.ohiostate.edu/ohiofieldcropdisease/Mycotoxins/mycopagedefault.htmhttp://www.ca.uky.edu/agc/pubs/id/id139/id139.pdfhttp://www.ca.uky.edu/agc/pubs/id/id139/id139.pdfhttp://www.ca.uky.edu/agc/pubs/id/id59/id59.pdfhttp://www.ca.uky.edu/agc/pubs/id/id59/id59.pdf


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Stink bugs feed with piercing-sucking

mouthparts and inject salivary juices into the

plants as they remove plant sap. The stylet that

enters the plant forms two canals, the salivary

canal and the food canal. Damage by stink bugs

can be the result of both the sap removal and

digestive action of the salivary enzymes. Peeling

back the fruit skin above the feeding sites back

reveals that the damaged tissue is discolored and

corky. While stink bugs can feed on many

different parts of these plants, it is the direct

feeding on the fruits which is most damaging.

Although damage by stink bugs is most easily

seen as the fruits begin to ripen, damage often

occurs well in advance of fruit maturity.

Stink bugs overwinter as adults outside the field

in sheltered places. They become active when

temperatures approach 70F. They will feed and

reproduce on many weedy as well as cultivated

plants. Stink bugs move into these crops by

midsummer and can remain in production fieldsuntil frost. Celeste Welty at the Ohio State

University has evaluated 0.75% damaged fruit (3

damaged out of 400 fruit) as a threshold

applying an insecticide for stink bugs in

tomatoes.

There are several insecticides that are effective

against stink bugs on various crops. Most of the

pyrethroids are effective including those

containing lambdacyhalothrin,

zetacypermethrin, cyfluthrin, bifenthrin, and

gammacyhalothrin. The neonicotinoids

insecticides, Actara and Belay can also control

stink bugs on various labeled crops. Always

read and follow label instructiuons.

NUT CROPS

Walnut Bunch DiseaseBy John Hartman, Extension Plant Pathologist

and John Strang, Extension Fruit and Nut

Specialist

Bunchy shoots (witches brooms) with

proliferating and deformed branches, twigs and

leaves were observed on a 12-year-old Frank

heartnut tree this past week. Heartnut is a

variety of Japanese walnut Juglans ailanthifolia

var. cordiformis, grown by commercial nut

producers and hobbyists in Kentucky. Heartnut

fruits are consumed for their good taste and

health benefits and they are said to be high in

antioxidants, fiber, and protein. Heartnut shells,

when split open are heart-shaped (Figure 6).

Symptoms. Mature infected Japanese walnut

trees may at first produce brooms on scattered

limbs (Figure 7), but the disease can spread

throughout the tree. Small trees may be

completely consumed by the disease. Leaflets in

brooms are smaller than normal (Figure 8) and

are abnormally narrow, curled, or cupped and

often chlorotic (Figure 9). Fruits fall from

diseased trees prematurely or nuts fail to fill out

and have shriveled and blackened kernels.

Leaves on infected shoots often senesce earlier

in the fall (Figure 10). Infected black walnutsoften show no symptoms, but may grow more

slowly.

Cause. Bunch disease of walnut is caused by a

phytoplasma. A phytoplasma is an insect-

transmitted organism similar to a bacterium, but

lacking a cell wall and typically inhabiting plant

phloem cells. The walnut phytoplasma strain is

Figure 4. Brown stink bug complex, Euschistus tristigmus,

E. servus, and E. variolarius.

Figure 5. Stink bug damage to tomato (left) and pepper

(right).


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related to the Prunus X-disease pathogen. Black

walnut,J. nigra, is susceptible to infection by

walnut bunch, but is very tolerant to infections

and suffers little damage. Japanese walnut,J.

ailanthifolia, is also susceptible to infection, butis intolerant to infection and infected trees can

be severely damaged.

Nut growers who observe this disease in

Heartnut will want to prune out infected limbs atthe first opportunity. If the disease is

widespread in the tree, complete removal may

be needed. The insect vectors for walnut bunch

are unknown.

Figure 6. Japanese walnut, note the heart-shaped nuts

meats.

Figure 7. Japanese walnut tree with walnut bunch-

infected shoots. Witches brooms are present in the top

middle and top right of the tree.

Figure 8. Walnut bunch disease causing smaller leaves,

shoot proliferation, and abnormal growth compared to

normal foliage, lower left and right.

Figure 9. Chlorotic, deformed, and cupped Japanese

walnut leaves infected with walnut bunch disease.

Figure 10. Early fall senescence of walnut bunch disease

infected leaves.


7/9

HOUSEHOLD

Brown Marmorated Stink Bug Look-A-Likes

in KentuckyBy Ric Bessin

As people are alerted to brown marmorated stinkbug (BMSB) and keep a watchful eye out for

them, we are finding out that there are several

common look-a-likes that create someconfusion. This includes other common stink

bugs in Kentucky as well as squash bug, a leaf-

footed bug that many mistake for a stink bug.

Currently we have identified BMSB from Boyd,

Jefferson, Greenup, Fayette (single specimen

only), Carter and Rowan counties. This article

discusses some of the possible insects that may

be confused with BMSB.

Stink bugs are roundish, shield backed bugs with

5 segmented antennae. BMSB can be recognized

as a relatively large and flattened stink bug. It

gets its name from the marbled brown and gray

colors on its back. The underside is variable in

color but is much lighter than the upper side. In

some specimens the underside can be very light

in color. To distinguish it from other similar

stink bugs, it has two wide light-colored banded

areas on the antennae. The abdomen on the

BMSB extends past the wings such that there are

light colored triangles visible past the wingedges. The BMSB also has only one small tooth

along each leading edge of the thorax, and thistooth is just behind the eye. It is a stink bug and

will produce are cilantro-like odor when

disturbed. On warm days in the fall, this stink

bug is attracted to and can enter buildings in

large numbers. During the summer months it canbe a very serious pest of many fruit, vegetable,

nursery, and field crops.

One insect that has been mistaken as both a stink

bug and the brown marmorated stink bug is the

squash bug. However, the squash bug has an

elongate body rather than the roundish body of a

stink bug. Some specimens appear to havelighter bands on the antennae that can be

confused with the BMSB. On occasion, a fewsquash bugs may be found entering buildings.

Another non-stink bug that is common and

enters homes in the fall in Kentucky is the

western conifer seed bug. It is similar to the

squash bug in size but differs a bit in colorationand expanded tarsi on the hind legs. This home

invader belongs to the leaf-footed group of true

bugs. Its shape and coloration are distinct from

that of BMSB.

Brown stink bugs are common throughout the

state and are commonly found on many of the

same fruit, vegetable, and fields crops where

BMSB can be a pest. We actually have at least

three species of brown stink bugs in Kentucky

and they are common pests of many crops. TwoFigure 11. A brown marmoratedstink bug. Note the wide banding

on the antennae.

Figure 12. Squash bug. Some specimens have

been mistaken for stink bugs.

Figure 13. Western conifer seed bug (Joseph

Berger photo, bugwood.org).


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of the larger species of brown stink bugs can

have the last segment and a half of the antennae

darkened. However, they dont have the light-

colored bands on the antennae. Our brown stink

bugs are just a bit smaller on average than theBMSB. Brown stink bugs have a series of fine

teeth on the leading edges of the thorax. Brownstink bugs also dont attempt to enter homes in

large numbers like BMSB.

Another group of stink bugs are theBrochymena

species in Kentucky. There are several species in

Kentucky that are often found on trees or near

wooded areas. These are common and are about

the same size and color of the BMSB. Their

antennae may have some lighter spots, but not as

pronounced as the two banded areas found on

the antennae of BMSB. What clearlydistinguishes them from BMSB are the

pronounced teeth along the leading edge of the

thorax behind the head and just ahead of their

shoulders (aka. humeral angle). As with the

brown stink bugs, these are not known to be

attracted to buildings in the fall.

Another stink bug species that is foundoccasionally isMenecles insertus (sorry, but it

doesnt have a common name). This brown-

colored stink bug is a bit smaller than BMSBand does not have the light colored bands on theantennae. The front edge of the thorax is more

rounded than the other stink bugs and its color is

not the marbled brown of the BMSB. This stink

bug is not considered to be of economic

importance.

One of our beneficial stink bugs, and there are a

few that are beneficial, can also be mistaken for

the BMSB. This is the spined soldier bug. It

feeds on a wide variety of vegetable and fieldcrop pests. The spined soldier bug is a bit

smaller than BMSB, has a similar marbled

appearance but does not have the light bands onthe antennae. The spined soldier bug can also be

distinguished from other stink bugs by a dark

marking on the membranous part of the front

wings. When they overlap there is a brown mark

Figure 14. A Brown stink bug

(Euschistus sp.).

Figure 15. A Brochymena stink bug.

Note the toothlike projections along

the leading edge of the thorax.

Figure 16. Another Brochymena stink bug common

to Kentucky. Again note the teeth that are on the

front edge of the thorax just behind the head.

Figure 17. Menecles insertus, another

brown-colored stink bug in Kentucky.


9/9

near the tip of the wings that is visible in the

picture below.

Note: Trade names are used to simplify theinformation presented in this newsletter. No

endorsement by the Cooperative Extension Service is

intended, nor is criticism implied of similar products

that are not named.

Figure 18. Spined soidlier bug with the

dark marking on the membranous

portion of the front wings.

kentucky pest news, october 26, 2010

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