David Owens, Extension Entomologist, owensd@udel.edu and Bill Cissel, Extension Agent – Integrated Pest Management; bcissel@udel.edu
Alfalfa
Continue scouting for potato leaf hopper and hopper burn. Yellowing leaves are a sign that yield has been impacted. Thresholds are adjusted for plant height, the smaller the plant, the lower the threshold. As a general guide, use a threshold of 1 leafhopper in 5 sweeps for plants less than 3 inches tall and moving up to 1 leafhopper per sweep for plants greater than 7 inches.
Soybean
Bean leaf beetles, grasshoppers, and thrips are active in fields. A couple of Mexican bean beetles have been spotted in New Castle County. Recent conversations with entomologists from the South have indicated that our early season defoliation thresholds are pretty conservative, although they are currently at 30% defoliation pre-bloom. Thrips feeding is generally only a problem with field wide averages of 8+ per leaflet and in dry years where the plants are under water stress, which is not this year.