kentucky pest news june 26, 2012
TRANSCRIPT
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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
http://www.uky.edu/KPNhttp://www.uky.edu/KPNhttp://www.uky.edu/KPNhttp://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.uky.edu/KPN -
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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
http://www.ca.uky.edu/agcollege/plantpathology/ext_files/PPFShtml/PPFS-OR-W-14.pdfhttp://www.ca.uky.edu/agcollege/plantpathology/ext_files/PPFShtml/PPFS-OR-W-14.pdfhttp://www.ca.uky.edu/agcollege/plantpathology/ext_files/PPFShtml/PPFS-OR-W-14.pdfhttp://www.ca.uky.edu/agcollege/plantpathology/ext_files/PPFShtml/PPFS-MISC-7.pdfhttp://www.ca.uky.edu/agcollege/plantpathology/ext_files/PPFShtml/PPFS-MISC-7.pdfhttp://www.ca.uky.edu/agcollege/plantpathology/ext_files/PPFShtml/PPFS-MISC-7.pdfhttp://ccesuffolk.org/assets/Horticulture-Leaflets/Impatiens-downy-mildew.pdfhttp://ccesuffolk.org/assets/Horticulture-Leaflets/Impatiens-downy-mildew.pdfhttp://ccesuffolk.org/assets/Horticulture-Leaflets/Impatiens-downy-mildew.pdfhttp://ccesuffolk.org/assets/Horticulture-Leaflets/Impatiens-downy-mildew.pdfhttp://ccesuffolk.org/assets/Horticulture-Leaflets/Impatiens-downy-mildew.pdfhttp://www.ca.uky.edu/agcollege/plantpathology/ext_files/PPFShtml/PPFS-MISC-7.pdfhttp://www.ca.uky.edu/agcollege/plantpathology/ext_files/PPFShtml/PPFS-MISC-7.pdfhttp://www.ca.uky.edu/agcollege/plantpathology/ext_files/PPFShtml/PPFS-OR-W-14.pdfhttp://www.ca.uky.edu/agcollege/plantpathology/ext_files/PPFShtml/PPFS-OR-W-14.pdf -
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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