Bill Cissel, Extension Agent – Integrated Pest Management; bcissel@udel.edu
Scout Alfalfa for Potato Leafhoppers
Continue to sample alfalfa for potato leafhoppers. Sample weekly starting seven days after the first cutting until final harvest. Ten sweep net samples should be taken in 10 random locations throughout the field when the alfalfa is dry. The threshold for alfalfa 3” or less is 20 leafhoppers per 100 sweeps, 4-6” tall is 50 per 100 sweeps, 7-10” tall is 100 per 100 sweeps and greater than 11” is 150 per 100 sweeps. If the field is more than 60 percent bud stage or if it has experienced “hopper burn”, the alfalfa should be cut instead of sprayed.
For more information on the identification, biology, and management of potato leafhoppers, please review our fact sheet: http://extension.udel.edu/factsheets/potato-leafhopper-control-in-alfalfa/
Here is a link to our Insect Control in Alfalfa Recommendations (pure stands only): https://cdn.extension.udel.edu/wp-content/uploads/2012/05/18063238/Insect-Control-in-Alfalfa-final-for-2017.pdf
Here is a YouTube video discussing how to sample for potato leafhoppers: https://youtu.be/7ybclcNu2rA
Soybeans
Continue to sample soybeans for defoliating insects including green clover worms, grasshoppers, silver spotted skippers, bean leaf beetles, and Japanese beetles. During vegetative growth stages, the threshold for defoliating insects is 30% defoliation. Once the plants begin blooming and during pod fill, the threshold is 15% defoliation. When several defoliating insect pests are present, combine the damage from all the pests when determining if your field is at threshold. To estimate the percentage of defoliation, randomly look at leaves from the whole plant, not just the new leaves.
Silver Spotted Skipper (last week’s Guess the Pest)
Green Clover Worm
Japanese Beetles
Here is a link to our Soybean Insect Management Recommendations for chemical control options:
https://cdn.extension.udel.edu/wp-content/uploads/2012/05/18063934/Insect-Control-in-Soybeans-2017-final.pdf