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Stink bug numbers growing in Missouri soybean fields

Agriculture.com Staff 12/22/2006 @ 9:03am

The proliferation of stink bugs has one University of Missouri entomologist sniffing around for a solution.

Wayne Bailey, an associate professor of plant sciences, said he is unsure why the number of stink bugs in soybean fields in Missouri is increasing, but if scientists don't get a handle on the problem the insects could affect yields.

"There are a number of reasons why we could be seeing more stink bugs," he said. "It could be all those reasons or none. We really don’t know why."

Stink bugs are "pod-feeding" insects equipped with a piercing, sucking mouth part that probe plant stems, leaves and pods and suck out their juices, Bailey said. Although there are three species of stink bugs commonly found in Missouri -- green, brown and Southern green -- it's the green variety that is causing soybean growers the most angst.

Damaged plants are generally found on the edge of the field, typically in the first 25 to 30 rows. Bailey said some brown stink bugs have been found in the center of some fields, but they aren’t a threat to soybeans.

Green stink bugs "can cause problems with plant growth," he said. Damaged plants often exhibit delayed senescence, in which the entire plant remains green after nearby undamaged plants damaged plants dry down. This can cause harvest problems.

About three years ago, MU entomologists used to catch one to three adult stink bugs a night using a black light trap in area soybean fields. Recently, the numbers have reached as high as 60 a night during the growing season, Bailey said. The numbers are even higher in Arkansas, Georgia and Louisiana.

Bailey suspects the increase is due to a combination of factors, including more no-till practices, which allow fields to go undisturbed providing insects such as stink bugs more opportunity to reproduce. Warmer weather and the normal fluctuation of insect populations also might explain the proliferation of the pest. So might farmers planting more glyphosate-tolerant soybeans and allowing weeds to grow later in the spring, giving stink bugs more places to hide and multiply.

Bailey said producers can get a jump on stink bugs by scouting their fields every seven to 14 days through the growing season. Admittedly, that's tough to do for most farmers due to time restrains, he said.

"Most producers are very good at scouting once they know an insect problem exists in the area," Bailey said. "I recommend that producers begin scouting with the emergence of any field crop. A majority of insect damage to most field crops occurs on seedling plants from the time of emergence through early growth stages."

In general, stink bugs are tough to kill with insecticides because they tend to hide deep in the foliage where sprays often don’t reach, Bailey said. They also winter in surrounding weeds and wooded areas near farm fields.

Entomologists don't use the black light as a tool for determining the actual field number of insects because the light only attracts adult stink bugs, not immature nymphs. "The black light is more of an indicator to entomologists as to what insects are flying to provide a rough estimate of stinkbug population levels," Bailey said.

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