kentucky pest news november 1, 2011

8/3/2019 Kentucky Pest News November 1, 2011

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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

http://www.uky.edu/KPN



http://www.ca.uky.edu/agcollege/plantpathology/ext_files/PPFShtml/PPFS-MISC-5.pdf



http://www.ca.uky.edu/agcollege/plantpathology/extension/pubs.html











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.



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.



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.

kentucky pest news november 1, 2011

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