Sweep nets can be used to sample potato leafhopper numbers in alfalfa.
Potato leafhoppers are showing up in eastern South Dakota alfalfa fields, says Ada Szczepaniec, Extension entomologist with South Dakota State University.
Minnesota and Nebraska growers are already dealing with high numbers of the pests and some have had to treat for them, she adds.
Potato leafhoppers are small, wedge-shaped, pale-yellow-to-green-colored insects that feed on plant xylem, causing V-shaped yellowing on the tips of alfalfa. Heavy populations of the pest can stunt plants and significantly reduce yield.
Second and third cuttings of alfalfa are usually the hardest hit, according to Szczepaniec. She suggests growers scout fields every week following first cutting.
A grower should sample using a 15” sweep net and take 10 sweeps at 10 random locations within a dry field. The entomologist advises walking in a “U” pattern and avoiding field margins.
After swinging the net to force insects to the bottom, a grower should grasp it about 10” from the bottom.
“Count the potato leafhoppers while slowly opening the net,” she says. “They are going to be jumping out fast, but if you unfold the net slowly, you will be able to count them.”
Only pale green or yellow leafhoppers should be counted and the average number captured per 10 sweeps calculated. Szczepaniec recommends using University of Nebraska tables to decide whether chemical treatment is economical.