Agronomic Crop Insects – July 13, 2012

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

Alfalfa
Continue to scout fields on a weekly basis for leafhoppers. It is also time to start watching for defoliators in alfalfa, including grasshoppers, corn earworm, webworms and beet armyworm.

Soybeans
In full season as well as soybeans planted after barley, the major defoliators continue to be Japanese beetles and green cloverworm. We are also starting to see an increase in bean leaf beetles and blister beetles. In double crop soybeans planted behind wheat, grasshoppers continue to be the predominant defoliator present at this time. Remember, at the bloom to pod fill stage in full season soybeans, the defoliation threshold drops to 10-15% defoliation. Double crop soybeans can not handle as much defoliation as full season fields at the pre-bloom or pod-fill stages.

Economic levels of spider mites continue to be found in both irrigated and dry land fields in Kent and Sussex counties. It is important to continue to scout the entire field since hot spots can be found throughout fields and edge treatments may not be effective. As a reminder, under heavy mite pressure and extended hot, dry weather, it often takes extended periods of free moisture on leaves, high humidity during the day and cool evening temperatures to get an increase in the fungal pathogens that can significantly reduce exploded mite populations. If egg populations are high at the time of application, two applications will mostly likely be needed. Be sure to read the labels for use rates and restrictions – there is a limit on the number of applications as well as the time between applications on all of the materials labeled for spider mite control. Lastly, be sure to consult your crop insurance provider regarding their rulings this year regarding the need to make an attempt to control mites under drought stress conditions.

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