Potato leafhopper adults have been observed in alfalfa fields in Ohio. These adults have likely begun laying eggs, and it only takes about 3 weeks for these eggs to hatch into nymphs and develop into adults. Populations of PLH will begin increasing. The second and third crops of alfalfa each year are the most vulnerable to this serious insect pest.
Growers should begin scouting their alfalfa fields now within the first two weeks after the first harvest. New spring seedings of alfalfa must be checked regularly, as they can be extremely damaged by relatively low numbers of PLH. Action thresholds can be exceeded very quickly in these slow-growing new stands. Once damaged, PLH can impact their growth for the rest of the year. The PLH can also reduce root growth and development in the seeding year that might impact the alfalfa yield potential in future years.
Proper scouting must be done with a standard-sized sweep net. For a video on scouting techniques visit: https://forages.osu.edu/video/scouting-potato-leafhopper-alfalfa
If alfalfa is more than seven days from a cut and plants are under normal stress, a good rule of thumb for an action threshold for treatment is when the number of PLH (nymphs+adults) in a 10-sweep set is equal to or greater than the height of the alfalfa. For example, if the alfalfa is 10 inches tall, and the average number of PLH per sample is 10 or higher, treatment is warranted. If the average is nine or lower, the grower should come back within a few days to see if the population is continuing to increase (treatment warranted), staying the same (come back again in a few days), or declining (treatment not warranted). Vigorous alfalfa can tolerate higher numbers, and stressed alfalfa can tolerate fewer, so you may need to adjust your action threshold based on the condition of the alfalfa.
For a video with detail on damage, ID, and control options visit: https://forages.osu.edu/video/potato-leafhopper-identification-and-damage-alfalfa
Ohio State University Extension’s factsheet on potato leafhopper in alfalfa is at: https://ohioline.osu.edu/factsheet/ENT-33
An excellent resource for other forage-related questions is the OSU Extension’s Forage Page at: https://forages.osu.edu/home