Now is a good time to start scouting for potato leafhopper in alfalfa, as second-cut alfalfa grows. Potato leafhoppers migrate up from the south in late spring to early summer. While they may be present in first-cut alfalfa they’re seldom a problem. But in the second-cut alfalfa numbers can increase rapidly. Younger alfalfa is more susceptible to damage at lower leafhopper numbers. Also, vigorous alfalfa can tolerate higher numbers, and stressed alfalfa can tolerate fewer – an important consideration should the current dry conditions continue. If alfalfa is more than 7 days from a cut and plants are under normal stress, a good rule of thumb for a treatment threshold is: when the number of leafhoppers in a 10-sweep set is equal to or greater than the height of the alfalfa. For example, if the alfalfa is 8 inches tall and the average number of leafhoppers per sample is 8 or higher, treatment is warranted. If the average is 7 or lower, the grower should come back within a few days to see if the population is higher or lower. While we don’t have specific guidance for thresholds in stressed alfalfa, consider the guidelines above and lower them some.
For a comprehensive list of products labeled in different field crops, their active ingredients, and scouting/threshold guidance, download the Michigan/Ohio State Field Crop Insect Pest Management Guide at https://aginsects.osu.edu/extension-publications/msuosu-ipm-guide
For a video on scouting technique visit https://forages.osu.edu/video/scouting-potato-leafhopper-alfalfa?width=657px&height=460px&inline=true#colorbox-inline-51399545
For a video with detail on damage, ID, and control options visit https://forages.osu.edu/video/potato-leafhopper-identification-and-damage-alfalfa?width=657px&height=460px&inline=true#colorbox-inline-397628030
Our extension factsheet on potato leafhopper in alfalfa is at https://ohioline.osu.edu/factsheet/ENT-33
A great resource for other forage-related questions is the Forage Page at https://forages.osu.edu/home