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Online at: www.uky.edu/KPN
Number 1288 November 1, 2011
ANNOUNCEMENT
-New Publication
CORN-Corn Seed Treatment for Nematodes
ANNOUNCEMENT
New Publication
By Cheryl Kaiser
A new publication, Foliar Fungicide Use in Corn
and Soybean (PPFS-MISC-05), is now available at
http://www.ca.uky.edu/agcollege/plantpathology/e
xt_files/PPFShtml/PPFS-MISC-5.pdf . It can also
be accessed via the publications page of the Plant
Pathology Extension Web site. The authors are
Drs. Donald Hershman and Paul Vincelli,
Extension Plant Pathologists. This fact sheet
discusses the use of fungicides for controlling
various corn and soybean diseases, the importance
of making a disease risk assessment, and thepotential for negative impacts of unnecessary
fungicide applications. In addition, recent ‘plant
health’ claims made by some fungicide
manufacturers are addressed.
CORN
Corn Seed Treatment for NematodesBy Paul Vincelli
This article provides a short review of nematicidal
seed treatments for corn. Nematodes are
microscopic roundworms that attack roots of thecorn plant (Fig 1). There are two products
currently on the market:
SOYBEAN
-Western Corn Rootworm ‘Soybean Variant’
Surveillance in Kentucky, 2011
Avicta® productsThese include Avicta® Duo and Avicta®
Complete Corn seed treatment. The nematicidal
active ingredient in these products is abamectin.Both products also contain an insecticide, and
Avicta® Complete Corn also contains a fungicide.
Based on the available published data,
performance of Avicta® against nematodes in
corn and other field crops is erratic. In the
majority of tests, Avicta® provided no statistically
significant reduction in nematode numbers or in
crop performance. However, in some tests,
abamectin does indeed provide a statistically
significant reduction in nematode number or
reproduction, and sometimes this results inimproved crop performance (improved root
weight, increased yield). Also, in some tests,
Avicta Complete Corn improves crop performance
not from nematode control, but from the
insecticide/fungicide component.
VOTiVO™ productsThe nematicidal active ingredient in VOTiVO™
products is a bacterium called Bacillus firmus.
Bacillus firmus is not a chemical poison, but rather
is a bacterium that forms a protective barrier that
may repel nematodes. It is currently sold only in apremix as Poncho/VOTiVO™, which also
contains an insecticide. There are very few
published studies on performance of Bacillus
firmus. Those that are available suggest results
are very erratic.
Lexington, KY 40546
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Are nematicide seed treatments worth using?
There isn’t a clear-cut answer. Here are some
things to consider:
• Soil populations of nematodes in
Kentucky vary greatly from field to field(see Figure 2, for an example). So it is
hard to know which fields have the
greatest threat from nematodes unless the
fields are sampled every year or two,
which most producers aren’t doing.
• Nematodes are a greater risk in sandy
soils. Since Kentucky soils are generally
not sandy, we don’t have as much risk as
some regions of the USA. There still is
risk, just not as much as in sandy soils.
• These seed-treatment nematicides perform
erratically, and they are certainly notcheap.
Case Study: Scott County, 2011I visited several corn fields this past season with
very dramatic plant-to-plant differences in planthealth: some plants were healthy-green and knee-
high, others were chlorotic and severely stunted,
and others were in-between. Careful inspection
and follow-up lab work revealed a complex of stresses:
1. Fusarium rot of the mesocotyl, severing
the plant’s connection to the seedling root
system (Fig. 3). This forces the seedling
to rely prematurely on an underdeveloped
nodal root system.
2. Temporary drought stress soon after crop
emergence.
3. Some temporary zinc deficiency early in
crop growth.4. Low numbers of endoparasitic nematodes
in the roots of healthy plants, at least 2Xhigher numbers in the sick plants.
The nematode numbers alone were not enough tocause significant crop loss in a healthy, growing
crop, according to available nematode thresholds
for corn. However, in this case, it seemed
reasonable to conclude that the nematodes may
have been a factor. Fusarium rot of mesocotyl
tissue is a destructive disease, but its presence
usually suggests that one or more early season
stresses were present. Zinc deficiency is
obviously a candidate, but so are the nematodes,and they may have worked together to stress the
plants and allow Fusarium to attack. Once
Fusarium caused the mesocotyl rot and cut off the
seedling root system, a temporary drought caused
dramatic stunting in the sick plants but had little
effect on plants with a healthy mesocotyl and root
system.
Figure 1. "Head" of nematode,
showing the spear-like stylet (arrow)
that it uses to puncture plant cells.
gure 2. Range of populations of lance nematode in 33 Kentucky corn fields
ampled in 2009.
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Would a nematicide seed treatment have helped in
this case? No one can say for sure. But it might
have. Even reducing one of these stresses might
have been enough to keep the Fusarium from
attacking, allowing the plants to tolerate the
temporary drought conditions.
ConclusionMy experience in Scott County this year makes me
more open to the possibility that a nematicidal
seed treatment might occasionally be beneficial in
corn, particularly if multiple stresses occur during
stand establishment. However, this is not a
blanket endorsement for widespread use of these
products. I expect cases like Scott County to be
the exception, rather than the rule. Producers who
are considering these products will improve their
chances of getting a profitable return by using
them in fields where soil samples show moderate
to high nematode counts. So there still is value in
sampling for nematodes. Finally, there are quite abit more public data on performance of Avicta®
than VOTiVO™, so users of Avicta® have a more
solid research base for using the product.
SOYBEAN
Western Corn Rootworm ‘Soybean Variant’Surveillance in Kentucky, 2011By Ric Bessin, Doug Johnson, Jerry Brown,
Myron Evans, David Fourqurean, Clint Hardy,Carla Harper, Darian Irvan, Darrell Jones, Cam
Kenimer, Philip Konopka, Tom Miller, Andy
Mills, Traci Missun, and Diane Perkins
This past summer we worked with county agents
in thirteen counties (Ballard, Boone, Carlisle,
Carter, Daviess, Fulton, Hancock, Hickman,
Lewis, Livingston, Meade, Oldham, Trigg) to
monitor soybean fields for the ‘soybean variant’ of the western corn rootworm that is has become the
major corn pest in states to our north. This is
similar to our survey last year, but we included
four additional counties and lost one county with aretirement of an agent. We surveyed for thewestern corn rootworm beetle variant that moves
out of corn and into soybeans to lay its eggs.
Agents that placed yellow sticky cards placed in
several soybeans fields in each county found
extremely low numbers of western corn rootworm
beetles during a four-week period in the
midsummer. These results are consistent with
what we observed last year, with very low western
corn rootworm levels in soybeans. That means we
did not find any evidence that the ‘soybean
variant’ is a problem. In fact the results this yearare even lower (eg. better) than what we saw last
year!
Figure 3. Rotted mesocotyl (arrow), cutting off the seedling
root system emerging from the kernel (Photo: Alison
Robertson, Iowa State University).
Figure 4. Western corn rootworm pupae, larvae and root damage.
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The western corn rootworm is considered one of
our billion dollar pest due to the damage it causes
and the cost of resources used to control it.
Typically, most western corn rootworms remain in
corn after they emerge in early to late July. InKentucky they mate and the females lay their eggs
at the bases of corn stalks. The eggs then hatch thefollowing spring and the young larvae are only
able to move a short distance (less than a meter) to
find corn roots to feed on. Normally only a verysmall percentage of the population moves out of
corn and into soybean fields. Because of this and
the use of crop rotation, western corn rootworm
problems in Kentucky have been restricted to
fields that have been left in corn for several years.
Recently a biotype was discovered in Illinois and
Indiana where a substantial proportion of the
population moved to soybeans to lay their eggs.
The result being that first-year corn in these areas
is at risk to economic levels of root damage by
rootworms. This biotype is called the ‘soybean
variant’ of the western corn rootworm. Since this
initial discovery it has spread rapidly to the north
east into Michigan and eastward into Ohio.Movement to the south has been relatively slow.
This summer the county agents placed yellow
sticky cards in several soybeans fields in each of
these counties and checked those cards weekly.
Last year we discovered that although we can
detect the beetles in soybean fields along the Ohio
River, levels are far below those that would
require action. This year beetles were only
trapped in one county in northern KY (Boone), all
other counties found no beetles in their soybean
fields.
What this means for our corn producers is that
corn following soybeans is a little risk to westerncorn rootworms. While corn that follows corn is
still at potential risk to rootworm attack, simply
rotating corn and soybeans, or
corn/wheat/soybeans will effectively manage
western and northern corn rootworms in
Kentucky. In states to our north where the western
corn rootworm variant is a problem, growers may
need to manage this serious pest with rotated corn
as well as continuous corn.
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.
Figure 5. Western corn rootworm adult female.