kentucky pest news june 26, 2012

7/31/2019 Kentucky Pest News June 26, 2012

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Online at:www.uky.edu/KPN

Number 1308 June 26, 2012

CORN

-Aflaguard for Aflatoxin Control

TOBACCO-Update on Black Shank and Foliar Diseases

FIELD CROPS

-I Hate Crying WolfBut Forewarned is

Forearmed!!

CORN

Aflaguard

for Aflatoxin ControlBy Paul Vincelli and Don Hershman

The current dry conditions across much of western

Kentucky has some producers concerned about

potential aflatoxin problems. Aflatoxin is a

natural toxin and carcinogen produced in corn

(and other crops) infected by the fungus

Aspergillus flavus. Aflatoxin contamination infood and feed is regulated by the U.S. Food and

Drug Administration

(http://www.ca.uky.edu/agc/pubs/id/id59/id59.pdf)

.

When preharvest aflatoxin contamination occurs

in corn, it is most often associated with drought

and high temperatures, especially during grain fill.

Damage to the kernels increases the risk of

contamination.

A novel product called Aflaguard is beingmarketed for reducing aflatoxin contamination in

corn and peanuts. It consists of non-viable barley

seed coated with spores of a naturally occurring

strain ofA. flavus which is atoxigenic. This

means that this organism does not produce

aflatoxin. It is thought to otherwise behave like

toxin-producing strains ofA. flavus, outnumbering

ORNAMENTAL

-Disease Alert: Impatiens Downy Mildew Found

in Kentucky

DIAGNOSTIC LAB HIGHLIGHTS

INSECT TRAP COUNTS

the native, toxin-producing strains and displacing

them within the ear of corn. This helps to reduce

preharvest contamination. This approach is used

successfully for aflatoxin control in cottonseed

using another product, AF 36, which is a different

atoxigenic strain ofA. flavus.

Dr. Tom Isakeit of Texas AgriLife Extension has

evaluated Aflaguard in replicated, randomized

field trials, a challenging task for something as

complex as this issue. His research thus far showsthat, as expected, Aflaguard often (though not

always) reduces aflatoxin contamination in corn.

His studies, done in a year of severe drought,

show that these reductions sometimes result in an

economic benefit through a reduced discount on

the harvested grain, though sometimes not,

particularly when contamination levels are low.

Dr. Isakeit is continuing to test the product under

commercial conditions, under varying levels of

aflatoxin pressure.

Reducing mycotoxin contamination through theuse of a biocontrol agent in the field is biologicallya very difficult challenge, yet Aflaguard often

provides measurable and significant reductions in

aflatoxin contamination. To a microbiologist like

me, this is really impressive. However, there are

several complications in deciding where theproduct fits.

Lexington, KY 40546
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The product should be applied beforetasseling for optimal benefit, but aflatoxincontamination in Kentucky is often

affected by the conditions that occur after

silking.

The majority of Kentucky corn fields thatexperience heat and drought during grainfill generally dont develop significantaflatoxin contamination, so widespread

use may not make economic sense. And if

contamination potential is high, not even

Aflaguard can bring down levels tomake it safe for human consumption.

The atoxigenic strain requires moisture tobe activated to produce spores.

Application of the product during drought

conditions can result in control failure.

Thus, if a producer is concerned about the risk ofaflatoxin contamination, application of

Aflaguard prior to silking may help reduce

anxiety, and that may be enough justification to

use it. Plus, the product may sometimes improvemarketability of the grain. However, I dont

foresee widespread use of the product in

Kentucky, even under the drought conditions we

have seen this growing season.

Thanks to Tom Isakeit, Texas AgriLife Extension,

for reviewing a draft of this article.

TOBACCO

Update on Black Shank and Foliar DiseasesBy Kenny Seebold

Reports of black shank have risen sharply across

Kentucky over the past 7-10 days. We generallythink of black shank as a wet-weather disease, but

severe damage can occur during a drought and thisis the scenario we now face. Plants showing

symptoms of black shank now were probably

infected following a rain event after setting.

Plants with low-to-moderate levels of disease wilt

more quickly than healthy plants in hot weather or

ground with low soil moisture (Fig. 1). Once

wilted, heat and a lack of soil moisture result in

sudden and widespread mortality of plants.

Wilting and death can be so sudden that plants

remain green when they die, not showing the

yellowing that is characteristic of black shank.

The classic blackening of the stem from whichblack shank takes its name can be less pronounced

as well during a drought because of the quick

disease cycle. It is not uncommon to find few

symptoms above the soil line. Instead, girdling

lesions can be observed at or near the root tip (Fig.

2) and this is why water uptake is restricted,

causing plant death during the drought. Even

tobacco varieties with high levels of resistance to

the black shank pathogen (Phytophthora

nicotianae) such as KT 204, KT 206, KT 209, or

KT 210 will suffer greater-than-anticipated lossesunder hot and dry conditions. Infected plants pose

another risk to healthy plants around them because

they represent a source of inoculum that can

explode should significant rainfall occur later in

the season.

When black shank crops up after setting, a

fungicide application may be necessary to reduce

the potential for further losses (especially where

fungicides were not applied prior to transplanting).

These rescue applications will be most effective

on varieties with moderate-to-high levels ofresistance. Recommended fungicides include

Ridomil Gold SL, Ultra Flourish, or MetaStar

2EC. Applications should not be made after layby

(last cultivation) and need to be directed at the soil

and stems of plants for best control of black shank.

The fungicide should be incorporated as quickly

after application as possible, either mechanically

or by irrigation (natural rainfall or overhead

irrigation). Soils need adequate levels of moistureto activate fungicides and permit uptake into the

plant.

Dry conditions have kept foliar diseases in check

so far this season. Blue mold is not active in theU.S. at the moment. Target spot has yet to be

reported, and weve found just a few cases of

frogeye on burley, mainly in low-lying fields near

creeks and rivers. Dry weather should help keep

these problems in check for now; however, thesediseases could be problematic if we get rains later


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in the season particularly just before and after

topping. Quadris fungicide, applied at 8 fl oz/A,

will provide good control of target spot and

frogeye if applied at least once at around layby.

Try not to apply Quadris during the hottest parts ofthe day to avoid plant injury. A second

application may be needed at topping to help withthis disease if needed, and to suppress late-season

frogeye leaf spot should that disease be active.

Quadris should never be mixed with pesticides

formulated as emulsifiable concentrates (ECs) or

those that have high solvent levels to avoid the

risk of severe leaf burn. We have had some

reports of injury in Kentucky when Orthene is

tank-mixed with Quadris; however, many have

applied this combination with no ill effects. To be

safe, dont use Orthene and Quadris together in

hot and dry weather.

Blue mold is still being reported in North Carolina

but is not thought to be active elsewhere in the

United States. For Kentucky, the threat from blue

mold is low at this time. The weather has been

unfavorable for disease development, and should

remain this way during the week of June 21. Still,

growers should scout fields regularly and be

prepared to act if the disease is found.

For recommendations on the control of tobacco

diseases, please consult past issues of the

Kentucky Pest News, or the Kentucky-TennesseeTobacco Production Guide (ID-160), available at

http://www.ca.uky.edu/agc/pubs/id/id160/id160.pd

f.

Figure 1. Wilting of young tobacco affected by black shank.

Figure 2. Root necrosis on a 'KT 204' plant infect by P.

nicotianae.

FIELD CROPS

I Hate Crying WolfBut Forewarned is

Forearmed!!By Doug Johnson

Twospotted spider mites (TSSM) are an

occasional pest of soybeans and corn in Kentucky

(KY). They are present every year but only

important during hot, dry periods. Unfortunately,

this is the type of weather we currently have and

have had for several months. Additionally, states

to the north of us, including Nebraska and Iowa,

are already experiencing some problems. I have

not received information about spider mites on KY

field crops but have seen some large populations

in fruit trees (different mite but same

circumstances). I, therefore, think it wise for those

with field crops interest to keep an eye peeled for

this pest.

Figure 3. Twospotted spider mites on a soybean leaf.
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TSSM are greenish-white with two dark spots on

the back. Adults are about the size of salt grains.

Juvenile TSSM have six legs, but adults have eight

legs. Other species of spider mites also attack field

crops.

Spider mites become active early in the spring andremain active throughout the summer. They live in

thinly webbed colonies on the underside of leaves.

Occasionally, you will see web strands between

leaves. Hot, dry weather allows rapid population

growth with each generation taking about five to

seven days to complete.

Infestations tend to start on field margins near

broadleaf weeds and/or the side from which the

wind is blowing, as they may drift on a breeze.

They may then spread out in ever increasing spots

if the weather allows.

In corn, damage presents as yellow stippling on

the upper surface of the leaves. Heavy and / or

prolonged infestations may cause premature

drying resulting in loss of tissue, stalk breakage

and kernel shrinkage.

In soybean, injury could resemble herbicide

damage, foliar disease or nutrient deficiency.Feeding results in tiny yellow spots or stipples

which may turn orange. Multiple damaged spots

may merge in to larger areas of damage. Withsevere damage, leaves may turn brown and

eventually fall off. Spider mites reduce yields bycausing pod shattering, wrinkled seed and early

maturity.

Scouting is best done in times of prolonged hot

dry (low humidity) weather. In soybeans the most

important time is during the reproductive stages of

R1-R5 and where a synthetic pyrethroid

insecticide has been used. Shake plants over a

piece of white paper and look for tiny white

moving specks. A hand lens is very useful indetermining if the specks are actually mites. In

corn, scouting is much more difficult and less is

known about making a control decision. The mites

are no harder to find, simply follow the

instructions for soybean but using corn leaves.

One simply wishes to determine if the infestation

is only on the outer edges or is across the field.

Large and widespread, mite infestations usually

happen when hot, dry and low humidity conditions

have occurred early in the season (like this year!).

In these circumstances, scouting should start well

before R1 (soybean) and in younger corn. Coolertemperatures and high humidity allow a natural

fungus to control spider mites. Rainfall will helpthe plant tolerate the infestation but will not reduce

the mite population. Application of synthetic

pyrethroid insecticides and fungicides may worsen

the infestation because these insecticides dont

work well on mites and the fungicide may hamper

the natural occurring fungus that kills the mites.

If direct control is required, consider using an

organophosphate insecticide like chlorpyrifos or

dimethoate. If you must use a pyrethroid consider

bifenthrin. An application is warranted when most

plants are infested with spider mites and leafspeckling and discoloration are apparent.

Reference: Field Crop Insects. Iowa State Univ.

CES. CSI 0014. Jan. 2012

Photo: Frank Peairs, Colorado State Univ.,

bugwood.org

ORNAMENTALS

Disease Alert: Impatiens Downy Mildew Found

in KentuckyBy Nicole Ward

Downy mildew was confirmed in Franklin County

this week in a commercial landscape; stock plants

originated in Jefferson County. Thus, we suspect

that there are many undetected cases here in thestate.

Symptoms often begin as unthrifty, yellowing

plants that have few blooms (Fig. 4). Under

irrigated or humid conditions, the fungus-like

organism develops white growth on undersides of


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leaves (Fig. 5). Advanced symptoms include bare,

leafless stems that eventually die.

In last weeks article in KPN, I recommended that

homeowners and landscape managers remove anddestroy infected plants, as well as asymptomatic

impatiens in the immediate vicinity since earlysymptoms may be subtle. This is the best way to

reduce the inoculum load. However, if downy

mildew is observed in the landscape, nearby non-

infected plants may be treated with fungicides

such as Subdue Maxx, Segway, Heritage, or other

fungicide approved for water molds (oomycetes).

These plantings should be monitored carefully for

any signs of disease even after fungicide

treatment. Fungicides are not recommended for

infected plants.

Fungicide guides are available for:Commercial landscapes:

http://www.ca.uky.edu/agcollege/plantpathology/e

xt_files/PPFShtml/PPFS-OR-W-14.pdf

And home landscapes:

http://www.ca.uky.edu/agcollege/plantpathology/e

xt_files/PPFShtml/PPFS-MISC-7.pdf

For more information on impatiens downy

mildew, see

http://ccesuffolk.org/assets/Horticulture-

Leaflets/Impatiens-downy-mildew.pdf

Figure 4. Early symptoms of impatiens down mildew include

leaf yellowing that resembles a nutrient deficiency. Often,

white fungal growth is apparent on undersides of leaves

(Photo by D. Ferrin).

Figure 5. As symptoms advance, impatiens downy mildew

causes defoliation. Under humid or irrigated conditions,

white fungal growth can be seen on undersides of leaves

(Photo by A. Windham).

DIAGNOSTIC LAB HIGHLIGHTS

By Julie Beale and Paul Bachi

Agronomic samples during the past week includedpotassium deficiency and common rust on corn;

potassium deficiency, stress symptoms andsoybean cyst nematode on soybean; manganese

toxicity, tomato spotted wilt virus, black shank

and soreshin on tobacco.

On fruit and vegetable samples, we have

diagnosed anthracnose and black rot on grape;

Phytophthora crown rot and Phomopsis leaf blight

on strawberry; Rhizoctonia root/stem rot on bean;

Stewarts wilt on corn; bacterial wilt on cucumber;

Phytophthora crown rot on lettuce; bacterial leaf

spot and Alternaria leaf spot on okra; sour skin on

onion; bacterial spot on pepper; bacterial wilt,early blight, Septoria leaf spot, Fusarium wilt,

Rhizoctonia root rot, pith necrosis and tomato

spotted wilt virus on tomato; and Rhizoctonia

root/stem rot on watermelon.

On ornamentals and turf, we have seen black root

rot and Pythium root rot on catharanthus and
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petunia; Phytophthora crown rot on liriope;

Pythium root rot on miscanthus; bacterial soft rot

on daylily; Botryosphaeria canker on goldenrain

tree and juniper; Entomosporium leaf spot on

hawthorn; scab on crabapple; powdery mildew ondogwood; Cryptodiaporthe twig blight on

chestnut; Seiridium canker on Leyland cypress;Phomopsis twig blight on juniper; and Pythium

root rot on bentgrass.

INSECT TRAP COUNTS

June 14 - 21

Graphs of insect trap counts for the 2012 season are availableon the IPM web site at -

http://www.uky.edu/Ag/IPM/ipm.htm.View trap counts for Fulton County, Kentucky at -http://ces.ca.uky.edu/fulton/InsectTraps

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 0 0

Armyworm 2 2

Corn earworm 4 0

European corn

borer

0 0

Southwestern

corn borer

3 0

Fall armyworm 0 0

kentucky pest news june 26, 2012

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