I have received reports that appear to indicate an increase in brown marmorated stink bug (BMSB) activity in central Kentucky. This invasive bug, which has a wide host range, has been in Kentucky for about 5 years, but as yet has not become economically importance in grain crops. This is likely to change at some time, and it is best to not get caught unawares! At present, this pest is likely to be more important to soybeans and possibly corn that is grown in central and eastern Kentucky (Figure 1) as opposed to those grown in western Kentucky. You can keep abreast of the known distribution of this insect by checking with UK Extension Entomology Brown Marmorated Stink Bug in Kentucky Web site.
BMSB is mainly a threat because of its ability to develop very large populations. Bug-to-bug it is not a great deal more important than other brown or green stink bug, but its populations tend to be much larger. Like other stink bugs, BMSB begin moving into soybeans as plants start to bloom and BMSB populations grow to their largest numbers as pods are forming and filling. It is the damage to pods during feeding that is important.
BMSBs look similar to other brown stink bugs in shape and color, though they tend to be a bit larger. The most diagnostic characters for identification are the two small (but distinct) white strips on each antenna near the tip end. Also, along the rear sides are a series of black and white bands (Figure 2).
Sampling Soybean Fields
Sampling for stinkbugs in soybeans is rather straight forward and best done with a 15-inch sweep net. Sample several locations across the field taking 25 sweeps at each location. Count the number of stink bugs in each (25 sweep) sample and average them over the field. The treatment threshold for stink bugs during flowering and podfill (R1-R6) is an average of 9 per 25 sweeps.
BMSB tend to be highly congregated on the field margins. Though some will be found in the interior of a field, most of them will be in the outer rows. In many states edge applications have been found to be sufficient to control this pest.
These insects can be controlled reasonably well with synthetic pyrethyroid insecticides. In particularly difficult situations, mixtures of pyrethroids + neonics or pyrethroids + acephate may provide a little better control. You can find insecticides for use on stink bugs in soybeans in Insecticide Recommendations for Soybeans – 2014 (ENT-13), which is also available at your county Extension office.
By Doug Johnson, Extension Entomologist