STINK BUGS IN NEBRASKA CORN AND SOYBEANS
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 pest to a variety of crops in the southern United States . There seems to be a general trend of increasing stink bug populations in more northern states, and in 2007 there were reports of significant injury to field corn in Nebraska .
Nebraska Stink Bugs: The major stink bug species found in Nebraska corn and/or soybeans are the green stink bug, Acrosternum hilare , the brown stink bug, Euschistus servis , and the one-spotted stink bug, Euschistus variolarius . In general, a dult 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, but brown stink bug nymphs are yellow to tan with brown spots down the center of the abdomen. The one-spotted stink bug looks similar to the brown stink bug, except it has a small spot on the underside of the abdomen. Another brown stink bug, the spined soldier bug, Podisus maculiventris , is a beneficial predatory insect.
General Stink Bug Biology: Adult stink bugs overwinter primarily in leaf litter, under bark, or in wood piles. It is believed that the green stink bug migrates north. Brown and one-spotted stinkbugs 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. After feeding a few days, they 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. 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 reproductive stage corn by piercing the husk and feeding on the developing kernels from the beginning of kernel formation through milk stage, although the can feed through the hard dough stage. Damage appears as missing or shrunken kernels. Severe damage causes ears to curve (banana ears) (see CropWatch Newsletter No.08-13, June 6 & 13 for info on stink bug in seedling corn).
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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. |
I njury 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
Little research or experience with stink bugs is available in the northern parts of their range, including Nebraska, and even in the south the information is variable for corn and soybean. In general, thresholds are based on counts of large nymphs and adults, as those are the most damaging stages.
For Field Corn: Florida recommends that “for corn in the early silk through milk stage, treatment may be justified when there is 1 stink bug per 5 plants. From the end of milk through the hard dough stages 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 recommends the “corn is most sensitive to stink bug injury during ear elongation before pollen shed. The treatment threshold at this stage is 1 bug per 4 plants (25% infested plants). Once pollination occurs, feeding though 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 1 bug per 2 plants (50% infested plants)”.
For Soybeans: Thresholds for stink bugs on soybeans vary considerably by state, and also do not explicitly consider variable costs of control or market value. They range from 0.3/ft-row (IL) to 3/ft-row (WI), or 0.2/sweep (IN) to 6/sweep (OH) and are not consistent with respect to timing, row spacing, or soybean use (seed or grain). The most common threshold for stink bug in soybeans is 1 bug/row-ft during the reproductive stages. If thresholds are met, the standard insecticides registered for soybean should be effective.
Insecticides: Insecticide efficacy data for stink bugs in Nebraska is not available. Insecticides labeled for stink bug control in soybeans include; Baythroid 1.6 – 2.8 oz per acre, Cobalt 19-38 oz/a, Leverage 3.8 oz/a, Lorsban (southern green stink bug only on label) 2 pts/a, Mustang Max EC 3.2 – 4.0 oz/a, Proaxis 3.2 – 3.84 oz/a and Warrior 3.2 – 3.84 oz/a. Several of these products are available as generics under various trade names. Check with your local Ag dealer for generic products. All of the above except Lorsban are labeled for stink bug control in corn . Rates may vary slightly from soybeans. Check the label before using any insecticide. (TH&KJ)
SOYBEAN APHID UPDATE
Several growers and consultants have called in the last several days with reports of soybean aphids in fields. Usually what is described as fields with overall low numbers, but with areas of “hot spots” of 50 to 100 square feet where aphids are at or near threshold levels. Remember the economic threshold is an average of 250 per plant over the entire field. Hot spots come and go, so don't jump the gun and treat when the field average is below 250. That being said, aphids can reproduce very rapidly and the field should be checked at least twice a week. The 250 threshold should give producers 5-7 days of lead time before average numbers hit 600, which is about the point where yield loss begins. Aphids will be active though August, so now is the time to devote scouting efforts to this sometimes major pest. (KJ)
SOIL AND PLANT ANALYTICAL LAB CLOSES
A review of the Soil Plant Analytical Lab (SPAL) was recently completed by IANR administration. In this review several factors were examined to determine the future success of the lab including cost of operations, competition, and demand for the lab's services. Unfortunately, it was concluded that the demand for the lab services will continue to diminish as operational costs continue to rise. In light of this, IANR Administration has elected to cease the operations of SPAL effective immediately. Samples that have been received prior to July 18 will be completed and the results will be returned to the client as soon as possible. We sincerely thank the Soil and Plant Analytical Lab staff for their years of dedicated service to the university and the operation of the Soil and Plant Analysis Laboratory.
Mark Lagrimini, Professor and Head, Agronomy and Horticulture Department
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