Joanne Whalen, Extension IPM Specialist; jwhalen@udel.edu
Alfalfa
Continue to sample for potato leafhoppers on a weekly basis. The treatment thresholds are 20 per 100 sweeps on alfalfa 3 inches or less in height, 50 per 100 sweeps in 4-6 inch tall alfalfa and 100 per 100 sweeps in 7-11 inch tall alfalfa.
Soybeans
Continue to sample fields for bean leaf beetles, grasshoppers, green cloverworms, spider mites and thrips. Grasshopper populations have exploded, especially in recently harvested wheat and barley fields. Please refer to past newsletters for general treatment guidelines and control options.
With the recent dry weather, we are again finding low levels of mites in soybeans. Early detection and control is needed to achieve spider mite suppression. In addition to dimethoate and Lorsban, we now have Hero labeled on soybeans. The bifenthrin component in this mix is the material that will provide spider mite suppression. However, to be effective it should be applied before mites explode. Please refer to the label for use rates and restrictions – you will need the high rate for spider mite control. It should also be noted that the label states, “Do not make applications less than 30 days apart.” (http://www.cdms.net/LDat/ld80Q005.pdf). We have also submitted a request for an Oberon Section 18 for soybeans – we will let you know as soon as we hear anything from EPA.