Bill Cissel, Extension Agent – Integrated Pest Management; bcissel@udel.edu
Potato leafhopper populations have increased dramatically over the last couple of weeks. There has also been a lot of alfalfa knocked down over the past 7-10 days. If you recently cut your field, sample the re-growth as soon as it starts to green up, especially if your field was at or near threshold for leafhoppers before you cut it. Continue to sample all other fields on a weekly basis until the final cutting. To scout, 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): http://extension.udel.edu/ag/insect-management/alfalfa/
Here is a Youtube video discussing how to sample for potato leafhoppers: https://youtu.be/7ybclcNu2rA