Joanne Whalen, Extension IPM Specialist; jwhalen@udel.edu
Alfalfa and Grass Hay Crops
It is the time of year to watch for the first defoliators in 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. No thresholds are available; however, controls should be applied before significant defoliation occurs.
Soybeans
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. You will need to sample for both adults and nymphs when making a treatment decision. Available thresholds are based on beans that are in the pod development and fill stages. As a general guideline, current thresholds are set at 1 large nymph/adult (either brown or green stink bug) per row foot if using a beat sheet, or, 2.5 per 15 sweeps in narrow-row beans, or 3.5 per 15 sweeps in wide-row beans. Although we do not have thresholds for brown marmorated stink bugs (BMSB), we continue to use this threshold for the stink bug complex present for BMSB as well.
We continue to survey for Kudzu Bug and we still have not found any more in soybeans but we did find adult, eggs and nymphs on a kudzu patch in eastern Sussex County. So be sure to scout soybeans for this insect and follow the Kudzu Bug website – (www.kudzubug.org) for identification, treatment information in soybeans and new detections. So far, all of our detections this year have been in Sussex County.
As far as corn earworm, corn surveys in states to our south have indicated that the wet season could result in lower populations in soybeans this year. However, if the weather changes this could change as well. So be sure to check fields for corn earworm. 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 (http://www.ipm.vt.edu/cew/) which estimates a threshold based on the actual treatment cost and bushel value you enter.