As the season winds down, soybean growers need to continue scouting their fields, especially those later planted fields that will remain green well into September. As other fields in the area begin maturing and turning yellow, some insects will migrate to soybeans that are still green and continue their feeding. Two of those insects, with one being a complex, are second generation bean leaf beetles and the stink bug complex consisting of the green, the red shouldered, and perhaps the brown marmorated stink bug. These insects feed on the pods and seeds of the plant, causing direct damage to the harvestable part of the soybean. We calculate that losing only 1-2 seeds per plant will cost growers an economic loss because of the high price of soybeans and the relatively low cost of making an insecticide application. Indeed, based on observations over the past few years, Ohio growers are probably losing yield and thus money to these insects in late maturing soybeans.
Treatment to prevent pod damage from bean leaf beetle is based on the level of insect injury observed on the pods. Evaluation of pod injury should be based on inspection of all pods on 10 randomly selected plants. On each plant sampled, count the number of total pods and the number of pods exhibiting pod scar injury, and then determine the percent pod injury based on the 10 plants inspected. It is important to estimate percent pod injury on inspection of the entire plant. Treatment is justified if the percent pod injury is approaching 10-15%, and BLB adults are still present and still active. More information can be found at http://ohioline.osu.edu/ent-fact/pdf/0023.pdf .
Scouting for stink bugs should be done by walking into the field at least 100 ft from the field’s edge. Sampling should be taken as sets of 10 sweeps at 3 to 5 locations in a field. Both adults and nymphs should be counted together. Experience suggests that the brown marmorated stink bug is difficult to sample using sweep nets, so you might need to walk slowly through the soybeans and attempt to count the bugs directly on the plants. Insecticide treatments should be considered when an average of 4 or more adults or nymphs of all species are collected per 10 sweeps in regular soybeans. When grown for seed or are food grade soybeans, we suggest lowering the threshold to only 2 adult or nymphs per sample. For brown marmorated stink bug, control is suggested if you see 1-2 per row ft through at least the R4 stage. More information on stink bugs can be found at http://oardc.osu.edu/ag/images/StB_Factsheet_June_26.pdf .
When the decision to make a rescue treatment is made to prevent pod and seed injury to later maturing soybeans, there are numerous foliar insecticides to use for bean leaf beetle and stink bug control. Growers should also be aware of pre-harvest intervals for the insecticides, which range from 14 days to 60 days. The time period left before anticipated harvesting of a field might dictate the insecticide chosen. See Bulletin 545 for all insecticides labeled on soybean (http://entomology.osu.edu/ag/545/soy545.pdf ).