Joanne Whalen, Extension IPM Specialist; jwhalen@udel.edu
Alfalfa
Continue to scout fields on a weekly basis for leafhoppers.
Soybeans
We continue to see a number of defoliators (grasshoppers, blister beetles, Japanese beetles, green cloverworm, etc.) present in full season and double crop beans. As fields enter the bloom to pod fill stages, remember that the defoliation threshold drops. In addition, bean leaf beetle populations and defoliation significantly increased, especially from Greenwood north on the western side of the state. This insect can also feed on pods. Bean leaf beetles can clip pods or plant diseases may enter the pod through their feeding sites. This can result in seeds that appear shrunken, discolored, and moldy, resulting in a reduction in seed quality. Although we have not established thresholds for pod feeding in our area, the following link provides information that is used in the Midwest. (http://www.ipm.iastate.edu/ipm/icm/2000/8-21-2000/lblroof.html)
As indicated last week, continue to watch full season beans that are starting to set pods for stink bugs. We continue to see an increase in both brown and green stink bug populations. Economic damage 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. We are currently following the same guidelines that are being used in Virginia. Thresholds are also based on numbers of large nymphs and adults, as those are the stages most capable of damaging pods. 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.
Spider mites can still be found in fields throughout the state. Remember, early detection and multiple applications are often needed to achieve control.