Agronomic Crop Insects – August 1, 2014

Joanne Whalen, Extension IPM Specialist;

Alfalfa and Grass Hay Crops
Continue to watch for defoliators in all hay crops. Fall armyworm can cause significant damage in grass hay so be sure to watch carefully since early detection is important to achieve effective control with labeled products. In alfalfa, a number of defoliators can cause problems including corn earworm, fall armyworm, beet armyworm and webworms. Although there are no specific thresholds, as a general guideline if the crop is more than 2 weeks from cutting and 25 to 30 percent of the terminals are damaged, treatment is suggested.

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. When plants reach the R5 stage (seed fill), they will become even more attractive to stink bugs. Although the numbers are still low, we are starting to see an increase in Brown Marmorated stink bug populations along field edges that border woods in New Castle County. In past years, edge treatments have been effective if populations are detected early.

We continue to survey for Kudzu Bug but have not found any in soybeans or kudzu. However, the first bugs have been found on a Kudzu bug patch in Talbot County, Maryland so it does appear that populations were able to overwinter in some locations. In addition, the number of counties with detections has significantly increased in Virginia ( Be sure to scout soybeans for this insect and follow the Kudzu Bug website – — for identification, treatment information in soybeans and new detections. The treatment threshold is still one nymph per sweep.

We continue to hear reports from the south about fall armyworms (FAW) in double crop soybeans (especially wheat beans). In Sussex County, we are starting to hear about a few fields with increased levels of FAW as well. They will act as defoliators so watch for defoliation from this insect since there are no established thresholds for numbers per sweep. Although corn earworm trap catches have not increased, we are starting to find corn earworm in full season and double crop fields so be sure to scout for corn earworm as well. When populations are high, corn earworm larvae also feed on soybean leaves so you should include them in the mix when scouting for defoliators. They can also feed on blossoms when populations are high before pod set. In the past, we have used the treatment threshold of 3 corn earworms per 25 sweeps in narrow fields and 5 corn earworms per 25 sweeps in wide row fields (20 inches or greater). These are static thresholds that were calculated for a 10-year average soybean bushel value of $6.28. A better approach to determining a threshold is to access the Corn Earworm Calculator ( which estimates a threshold based on the actual treatment cost and bushel value you enter.