Because of delayed planting and a cool summer,
Kentucky soybean producers are likely to have considerable acreage of late-maturing soybeans. This probably causes most folks to be concerned with frost. However, this extended maturity may also set up fields for additional damage by stink bugs. Producers and consultants should remain watchful as long as pods are still filling.
By far, the most common stink bug found in Kentucky is the green stink bug. Our research indicates that green stink bugs make up greater than 80 percent of the population. Nonetheless, there are several species of brown stinkbugs in Kentucky-grown beans as well.
Stink bugs can cause decreases in both yield and seed quality. These pesky bugs feed directly on the bean using their piercing-sucking mouth parts. They puncture the pod wall and stab the developing bean, removing nutrients and sometimes allowing entrance of pathogens into the pod / bean. Usually, there is no clear evidence of this damage until the pods are mature. The only clear evidence one has of these important pests is observing them in the field; damage symptoms are too late.
Stink bugs will hang around until frost, feeding on whatever is available to them. In soybeans we consider the pods at risk up through to R6 stage. So if you have beans less mature than this you should definitely be looking for these critters. Once soybeans are in the R6 stage stink bug damage is much more difficult to predict.
Stink bug sampling in narrow or wide rows
In wide-row beans, a shake cloth, or drop cloth) may be used. This is a 3- foot long section of white cloth wide enough to reach from row to row. Shake the beans on both sides over the cloth and count the stink bugs that fall to the cloth. Adults can fly so you need to count quickly. Juveniles do not yet have wings so they are a bit slower to escape.
In narrow-row beans, use a sweep net. The 15-inch-diameter sweep net is the standard tool for most thresholds. Take 25 sweeps per location and count the stink bugs captured. In both types of sampling, each field should be sampled at multiple locations. The more locations you sample, the more accurate and precise your estimates will be. Average the number of stink bugs captured over all locations.
Thresholds that warrant control are when with a shake cloth an average of one stink bug per row foot, or if sampled with a sweep net, treat if you collect an average of 9 stinkbugs per 25 sweeps at R4-R6.
If control is required, synthetic pyrethroid insecticides are commonly used for control and are very effective on green stink bugs. Brown stink bugs are a bit more tolerant of pyrethroids. So if they are plentiful, inclusion of an organophosphate like acephate may be needed.
Producers in the central and eastern Kentucky production areas need to keep their eyes open for the two invasive stink bug species. Populations of the brown marmorated stink bug, or BMSB, have become established in central and eastern Kentucky over the last 3 years. BMSBs look typically like other brown stink bugs except that they are often a bit larger and have two small but very distinct white bands surrounding the joints in their antennae. In addition, the Kudzu bug has been found in three southeastern Kentucky counties bordering I-75. They are dark green to olive with a rounded shape and about the size of an English pea.
Neither of these species is believed to be of major importance in this year’s crop, but as their populations become established and grow larger in size they have the potential to become major soybean pests.