Certainly this is the time to be checking your soybeans for the presence of stink bugs. I have not noticed economically important problems in the beans I have sampled, but stink bugs are certainly common and our light traps have been capturing very large numbers compared to previous years (Figure 1). At Princeton in particular, the increase is greater than three times what we have captured in the past 2 years, and the season is not over. Black light trap data do NOT translate directly to numbers in the field! Nevertheless, this very large increase begs taking a look at the situation.
Soybeans are at some risk to stink bugs from beginning bloom until R6/R7stage. So, while full season beans are probably well advanced, there are lots of double-crop and late double-crop beans still at risk. For many, people the damage stinkbugs cause in grain is never noticed until the crop is harvested. This is because these sucking bugs feed directly on seed inside pods and cause very little obvious damage to plants. Losses are due to damaged and shriveled beans and aborted pods. It is therefore necessary to actually sample for the pest to determine if the plants are at risk.
Green Stink Bugs
Although we have several species of stinkbugs in our beans, it is the green stink bug that is most numerous. Adults are ½” long, green (and a few slightly smaller browns) with sucking mouthparts. The body is shield-shaped. Nymphs are wingless and are quite variable in color, but yellows and reds are common. Both adults and juveniles feed on plants.
Stink bugs are most often found in border rows and against woodlots. One may use a shake cloth to sample, but as we generally have narrow row beans (e.g. less than or equat to 15”), a 15” sweep is most often used. Using this sweep net, take a series of 25 sweeps in each location and sample in multiple locations within the field. At each location, count the number of stink bugs captured and average this number over the number of locations sampled in the field. Our threshold for recommending an insecticide treatment is 3 stink bugs per 25 sweeps at R1-R3 growth stage and 9 stinkbugs per 25 sweeps at R4-R6 growth stage. Treatment of more mature beans is not recommended. If insecticidal control is warranted, you may find a list of insecticides labeled for use in Insecticide Recommendations for Soybeans‐ 2014 (ENT-13), available online and at your county Extension Office.
Brown Marmorated Stink Bug
In addition to our “normal” stink bugs, brown marmorated stink bug (BMSB) is now well established in the central Kentucky region. My colleague in Lexington, Dr. Ric Bessin, has this year, for the first time, captured BMSB in his black light trap. In addition, he has seen them in soybeans and in fruit and vegetable plots on the UK farms. BMSB are also quite common on fruiting trees and ornamental plants in and around Lexington. These changes indicate that BMSB is adapting very well to our state and may yet develop into a major pest of crops and as a home invading pest. BMSB is still quite rare in the western half of the state. As far as grain crops are concerned, BMSB is counted just like any other stink bug for making spray decisions.
Sampling for Kudzu bug indicates that there is little or no risk of economic problems with this soybean pest this year. I have added one western KY county (Christian) to the list of counties where the pest is found. However, in all cases (including resampling of last year’s locations along the I-75 corridor), although the pest is present, populations are very small, and thus far, restricted to Kudzu.
Be reminded that sink bugs feed on a wide range of crops and ornamental plants. See Dr. Bessin’s article (Brown Marmorated Stink Bug Update) elsewhere in today’s KPN postings.
Doug Johnson, Extension Entomologist, University of Kentucky