Agronomic Crop Insects – August 12, 2016

Joanne Whalen, Extension IPM Specialist;

We continue to find low levels of defoliators (Japanese beetles, bean leaf beetles, grasshoppers, silver spotted skipper, green cloverworm, yellow striped armyworm and isolated spots of fall armyworm) in both full season and double crop soybeans. As a general guideline, treatment decisions for defoliators should be based on the following defoliation thresholds:

(a) Full Season Plantings – 30% defoliation pre-bloom; 15% defoliation from bloom through the end of pod fill; 35% – once fully developed seeds are present

(b) Double Crop Plantings (especially if growth is poor) – 20% defoliation pre-bloom, 10% defoliation from bloom through pod fill; 15% defoliation – once fully developed seeds are present.

Another defoliator that we are starting to find is the soybean looper. This insect is a migratory pest and in past years we have seen it cause significant defoliation in outbreak years. It is often a problem in dry years. Since resistance to pyrethroids has been documented in states to our south, a non-pyrethroid option will need to be selected if they become a problem. We also have other looper species in our fields so proper identification is important. The following link from Virginia includes pictures to help with identification

Continue to watch for an increase in stinkbug populations. Economic damage from stink bugs is most likely to occur during the pod development and pod fill stages. As far as BMSB, we are only finding a few in fields in New Castle County so far. For management of BMSB in soybeans, please read the following bulletin:

We continue to survey for Kudzu Bug but have not found any in soybeans or kudzu. In Virginia, kudzu bugs have been found in soybean fields in 22 counties ( but none have been found near threshold levels. Be sure to scout soybeans for this insect and follow the Kudzu Bug website – — for identification and treatment information. The treatment threshold is still one nymph per sweep.

If we see a return to cooler temperatures in August, be sure to watch for soybean aphids. Cooler weather patterns favor an increase in populations. The economic threshold for soybean aphid established in the Midwest is 250 aphids per plant. Populations should be increasing and most of the plants should be infested (>80 percent) in order to justify an application. This threshold is appropriate until plants reach mid-seed set (R5.5). Spraying at full seed set (R6) has not produced a consistent yield response in the Midwest. You should also consider beneficial insect activity before making a treatment decision. Most products labeled for soybean aphid will provide effective control

As far as corn earworm, we continue to find low levels of small larvae, mainly in double crop fields. Although trap catches are still moderate, we have seen an increase in a few pheromone traps so it is important to start scouting fields for corn earworm. In making a treatment decision, the use of the Corn Earworm Calculator – developed in VA and NC ( will provide the best decision making information since it estimates a threshold based on the actual treatment cost and bushel value you enter.