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Keep watch for these Southern invaders

Insects from the South are creeping northward. At least three insect pests that have been common in Southern soybean fields for years are finding their way more and more into Nebraska fields.

Here is a postharvest update on the current status of these potential soybean pests from University of Nebraska Extension entomology experts.

Stinkbugs

There are at least three species that are important in Nebraska, including brown, one-spotted and red-shouldered stinkbugs. Others found in the state include green, dormant and twice-stabbed stinkbugs.

“Reports of stinkbugs in Nebraska corn and soybeans have been increasing the last few years,” says Tom Hunt, University of Nebraska Extension entomologist at Haskell Ag Lab, Concord. “Therefore, the Nebraska Soybean board funded a study to assess the damage potential for stinkbugs in Nebraska and to develop a stinkbug integrated pest management program.”

Hunt says that the adult stinkbugs overwinter in leaf litter, under bark or in wood piles. The green stinkbug is believed to migrate north.

“Nymphs and adult stinkbugs injure soybeans by puncturing various soybean plant parts and extracting plant fluids,” he says. Injury often first appears in field borders as bugs move into the field.

Dectes stem borer

The adult Dectes stem borer is a gray, elongate beetle about one-half inch long with antennae that are longer than the body.

“The soybean stem borer has been in south-central Nebraska for several years, coming up from Kansas,” says Keith Jarvi, UNL Extension educator at Dakota, Dixon and Thurston counties. “Not a whole lot can be done with them, because no chemical control is working,” he says. “If it spreads, it could be a real headache, as there is no good control method.”

Jarvi says that the larvae tunnel into the main stem, causing soybeans to lodge late in the year, making harvest difficult. Early harvesting might be one strategy to curb stem borer losses.

“They do not seem to affect yields that much because they move in very late in the growing season,” he says.

Kansas State University is conducting research on a number of potential control measures, Jarvi says.

Green cloverworms, webworms

The cloverworm larva, which is pale green with two white longitudinal stripes on each side, and the webworm, which is a light green caterpillar with a light stripe and small dark green spots, do damage as defoliators.

“Cloverworms and webworms are kind of sporadic pests,” says Mike Rethwisch, UNL Extension educator in Butler County. “We might have populations of them and then go years without seeing them. They are not pests we expect to see in large numbers. This year, we had green cloverworms not only in soybeans, but also in alfalfa, and we had them at the same time we had garden webworms in soybeans.”

Rethwisch observed webworms completely defoliating soybean plants in July that were adjacent to drowned-out plants standing in water. “But I didn’t find any soybean fields that necessitated treatment,” he says.

However, there were alfalfa fields that did reach economic threshold for a combination of cloverworms and webworms this season.

Most of these pests migrate into the state and do not overwinter here. For those that do overwinter, open, cold winters with fluctuating temperatures are hard on them, Jarvi says.

“Last year’s snow cover probably moderated temperatures and helped survival in some areas. Still, many times the weather at egg laying or infestation time is often the most important factor,” he says.

To learn more

For more information on soybean pests in Nebraska, visit the UNL Department of Entomology Web page at entomology.unl.edu/
extension/crops/soybean.shtml
.

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Green cloverworm

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Stinkbug

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Dectes stem borer larva

This article published in the December, 2010 edition of NEBRASKA FARMER.

All rights reserved. Copyright Farm Progress Cos. 2010.