Stink Bug Populations Developing in Soybeans and Corn - UNL CropWatch, Aug. 4, 2011

Stink Bug Populations Developing in Soybeans and Corn - UNL CropWatch, Aug. 4, 2011

August 4, 2011

Reports of stink bugs in Nebraska corn and soybean have been increasing the last few years. In the past, stink bugs have not been considered a significant pest of corn or soybean in Nebraska, but they are economic pests to a variety of crops in the southern United States. Over the last five to ten years there appears to be a general trend of increasing stink bug populations in more northern states, including Nebraska.

Green stink bug

Green stink bug   (All photos from UNL Department of Entomology)

Brown stink bug

Brown stink bug

Spined soldier bug

Spined soldier bug, another brown stink bug, is a beneficial predatory insect.

To address this developing situation, the Nebraska Soybean Board funded a study to assess the damage potential for stink bugs in Nebraska and to develop a stink bug integrated pest management program.

We have not had reports of economically damaging stink bug populations this year, but populations are growing. Soybeans are probably most susceptible to injury, but we have had a few reports of problems in vegetative and reproductive stage corn the last couple of years.

Nebraska Stink Bugs

Surveys conducted in Nebraska from 2009 to 2011 indicated that four main species of stink bugs are found in Nebraska soybeans and corn. They are the green stink bug, the brown stink bug, the onespotted stink bug, and the red-shouldered stink bug. All are shield-shaped as nymphs and adults.

In general, adult green stink bugs are bright green, and adult brown stink bugs are brown with a yellow or light green underside. Green stink bug nymphs change color and pattern as they grow. Brown stink bug nymphs are yellow to tan with brown spots down the center of the abdomen. The onespotted stink bug looks similar to the brown stink bug, except it has a small spot on the underside of the abdomen. The red-shouldered stink bug is green and has a red stripe across the base of the wings. Another brown stink bug, the spined soldier bug, is a beneficial predatory insect.

General Stink Bug Biology

Adult stink bugs overwinter primarily in leaf litter, under bark, or in wood piles. We believe that the green stink bug does not overwinter in Nebraska, but migrates north in late spring to early summer. We typically begin to find the green stink bug in July. Brown, one-spotted, and red-shouldered stinkbugs, as well as a few other recently collected species, appear to overwinter in Nebraska.

In the spring, adult stink bugs leave the overwintering sites and feed on a variety of wild and cultivated hosts. In Nebraska crops, the first appearance of significant numbers of bugs in the spring is in wheat, followed by alfalfa. After feeding a few days, stink bugs mate and lay clusters of eggs. As the season progresses, female stink bugs are attracted to a variety of flowering plants, including corn and soybean. Populations in corn and soybeans peak during the pod filling stages of soybean and ear filling stages of corn. There are likely one to two generations in Nebraska, depending on species.

Stink Bug Injury to Corn and Soybean

Stink bugs have piercing and sucking mouthparts and feed by piercing a plant part (or another insect in the case of the spined soldier bug), injecting digestive enzymes, and removing fluids.

Nymphs and adult stink bugs injure vegetative stage corn by feeding at the base of the seedling corn plant. Feeding results in irregularly shaped oblong holes with yellow margins in the leaves as they emerge from the whorl, twisting of the whorl, and in some cases, death of the growing point. Nymphs and adult stink bugs damage reproductive stage corn by piercing the husk and feeding on the developing kernels from the beginning of kernel formation through milk stage, although they can feed through the hard dough stage. Damage appears as missing or shrunken kernels. Severe damage causes ears to curve (banana ears).

Nymphs and adult stink bugs injure soybeans by puncturing various soybean plant parts and extracting plant fluids. They prefer young tender growth and developing seeds. As they feed, they inject digestive enzymes, which cause deformation and abortion of seeds and pods, and predispose the feeding site to various pathogens. In addition, stink bugs can cause delayed maturity and deformed leaf growth. Yield and quality losses depend on when the bugs injure soybean, and can be severe.

Injury often appears first on field borders as the stink bugs move into the field (both corn and soybean fields). With time the stink bugs can move throughout the field.

Management of Stink Bug in Corn and Soybean

In general, thresholds are based on counts of large nymphs and adults, as those are the most damaging stages. Green stink bugs are more numerous in soybeans and brown stink bugs are more numerous in corn, but don’t be surprised to find a mix of species.

For Soybeans

Thresholds for stink bugs on soybeans vary considerably by state, and do not explicitly consider the variable costs of control or market value of the crop. They range from 0.3 stink bug per ft-row (Illinois) to three stinkbugs per ft-row (Wisconsin), or 0.2 stink bugs per sweep (Indiana) to six per sweep (Ohio). Recommendations are not consistent with respect to timing, row spacing, or soybean use (seed or grain).

The most common threshold for stink bugs in soybeans is one bug per row-ft during the reproductive stages. We believe this is the most appropriate for Nebraska. If using a sweep net, the threshold is 3.6 stinkbugs per 15 sweeps (0.25 bugs per sweep).

For Field Corn

Florida recommends that “for corn in the early silk through milk stage, treatment may be justified when there is one stink bug per five plants. From the end of the milk stage through the hard dough stage treatment may be justified when there is an average of one stink bug per plant. Only stink bugs 1/4 inch or longer should be considered when determining thresholds.”

Georgia notes that “corn is most sensitive to stink bug injury during ear elongation before pollen shed. The treatment threshold at this stage is one bug per four plants (25% infested plants). Once pollination occurs, feeding through the husk causes damage to individual kernels. Kernels are susceptible to damage up until the milk stage (R3) and possibly early dough stage (R4). The threshold at this time is one bug per two plants (50% infested plants).”

Research is ongoing in Nebraska, but until we have more definitive information, use the treatment threshold of one bug per four plants (25% infested plants) prior to pollination, and one bug per two plants (50% infested plants) after pollination up to early dough stage.

If thresholds are met, the standard insecticides registered for corn or soybean should be effective.

Tom Hunt, Extension Entomologist, Haskell Ag Lab, Concord
Bob Wright, Extension Entomologist, Lincoln
Keith Jarvi, Extension Educator, Dakota, Dixon, and Thurston Counties