The alfalfa crop's No. 1 enemy is on the attack. The potato leafhopper has made it's northward migration from the sunny South and is in fields sucking the life juices from valuable alfafa plants right now. The bright green, wedge-shaped insects can cause hopper burn on leaves, stunting alfalfa plants. That can result in yellowing of alfalfa leaves and could cause significant yield loss and impact the plants' nutritional value, says Ron Hammond, Ohio State University extension entomologist.
Potato leafhoppers are an annual pest problem in Ohio in the spring as the pest migrates north from Gulf Coast states, carried on winds in storm systems.
"In alfalfa, potato leafhopper is definitely our No. 1 pest," Hammond says. "It's an insect that, if allowed to go past threshold and develop young population, can lead to damage such as stunting.
"Most growers have already had their first cutting, so now is the time for scouting for this pest because we know it has arrived in Ohio. Growers can begin scouting for the leafhopper once alfalfa regrowth reaches sufficient height for sweep-net sampling."
In glandular-haired, leafhopper-resistant alfalfa, the economic threshold is three times the normal threshold, or three leafhoppers per inch of growth. In that case, the threshold would be 18 leafhoppers for 6-inch tall alfalfa, Hammond says.
"If the resistant alfalfa is a new planting this spring, growers might want to use thresholds meant for regular alfalfa during the very first growth from seeding," he says. "After the first cutting, growers can then use three times the normal level threshold.
"Growers who take the time to sample and spray are better able to control the pests, while those growers who don't, tend to get hit by them."
More information on potato leafhopper, including how alfalfa-growing conditions might affect the threshold, can be downloaded.