Joanne Whalen, Extension IPM Specialist; jwhalen@udel.edu
Alfalfa and Grass Hay Crops
Be sure to watch for corn earworm, fall armyworm, beet armyworms and webworms — as well as any other defoliators. In addition to checking labels for rates, be sure to check for comments on control under high populations and size of larvae; days to harvest as well as forage/silage restrictions, as well as other use restrictions. Continue to watch grass hay fields for armyworms – especially on re-growth after cutting. Larvae must be small at the time of treatment to achieve effective control.
Soybeans
We are starting to get reports from consultants of economic levels of corn earworms in Kent and Sussex counties in Delaware and on the lower eastern shore of Maryland. Trap catches remain high throughout the state and moths can be found laying eggs in fields. In general, threshold levels are being found in drought stressed full season and double crop fields at this time. However, this could change quickly so all fields will need to be scouted since it appears we are the beginning of the egg hatch period. Since population levels vary from field to field, the only way to know if you have an economic level will be to scout all fields. Remember, corn earworms can feed on the foliage and blossoms as well as the pods. Although there is no threshold for corn earworm feeding on flowers or leaves, data from North Carolina has indicated that feeding on flowers can result in reduced yields by delaying pod set. When looking at foliage feeding by corn earworm, you will need to use defoliation as well as the presence of worms to make a decision (again – there is no worm threshold available for leaf and/or blossom feeding). Once pods are present, the best approach to making a decision on what threshold to use for corn earworm is to access the Corn Earworm Calculator developed at Virginia Tech (http://www.ipm.vt.edu/cew/) which estimates a threshold based on the actual treatment cost and bushel value you enter.