Agronomic Crop Insects – July 17, 2015

Joanne Whalen, Extension IPM Specialist; jwhalen@udel.edu

Alfalfa
Continue to scout fields on a weekly basis for leafhoppers. In past years, we have also seen an increase in thrips when weather conditions turn hot and dry. Reports from other areas of the country indicate that thrips feeding on the developing leaf tissue can cause the leaves to distort as they emerge. Leaves may also be curled, with a cupped or puckered appearance. Although there are no thresholds for thrips in alfalfa, the following information from other areas of the country may be helpful when considering the need for thrips management: “(a) high populations of bean or onion thrips may cause damage, especially in dryland conditions and (b) if a thrips treatment is contemplated, it is best to cut as soon as possible and treat the regrowth if the infestation persists. Thrips are very difficult to control in alfalfa, so excellent coverage is important and two applications may be required for satisfactory results.”

Soybeans
We continue to see a number of defoliators (grasshoppers, Japanese beetles, Oriental beetles, silver spotted skipper, bean leaf beetles and green cloverworm) present in full season and double crop beans. As full season fields enter the bloom to pod fill stages, remember that the threshold drops to 15% defoliation. As a reminder, double crop soybeans cannot handle as much defoliation as full season fields at the pre-bloom or pod-fill stages.

We are starting to see an increase in stinkbug populations (native green and brown). Very few brown marmorated stink bugs (BMSB) have been found except for an occasional adult on field edges near woods in New Castle County. 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.

Be sure that you continue to sample for mites since economic populations are starting to show up in hot spots throughout the state. We can find hot spots present both along field edges and in the interior of fields. Early detection and control before populations are exploded is necessary to achieve effective control. In addition, two applications may be needed to achieve control.

As part of our Delaware Soybean Board funded survey project, we are continuing to survey for Kudzu Bug. As of this week we have not detected any in the 75 fields soybeans we are monitoring statewide. In other states they are indicating in newsletters that kudzu bugs are showing up in very small numbers near traditional “hot spots” where they have overwintered. Please refer to the following link from North Carolina for more information on monitoring and decision making.

http://soybeans.ces.ncsu.edu/2015/07/kudzu-bugs-beginning-to-migrate-into-soybeans/?src=rss

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