Issue No. 10, Article 2/May 29, 2009
Don't Neglect Scouting of Alfafa for Potato Leafhoppers
In many areas of Illinois, late May and the arrival of potato leafhoppers coincide. These small (1/8-inch long), pale-green, "wedge-shaped" insects represent an important economic threat to alfalfa production each year. Potato leafhoppers are migratory and fly into Illinois each spring from southern states. The females can lay two to three eggs in the stems and veins of plants every day. The immature leafhoppers (nymphs) hatch after 7 to 10 days and subsequently reach maturity in roughly 2 weeks. Depending on temperatures throughout the summer, three to four generations of this pest occur each year in Illinois.
Potato leafhopper adult (Courtesy of Matt Montgomery, University of Illinois Extension).
Potato leafhoppers, with piercing and sucking mouthparts, remove fluids while also injecting toxins into a plant's vascular system. Plants that have been fed upon may display the characteristic "hopper burn"--a yellow V-shaped area at leaf tips. This symptom is often found on older leaves because damage may not become obvious for a few weeks following injury. Alfalfa that is severely damaged will become stunted and bushy.
Scouting alfalfa for potato leafhoppers and making subsequent sound management decisions requires the use of a sweep net. As few as 0.2 leafhoppers per sweep represents a potential economic threat in stands of alfalfa that have been harvested recently (stubble-alfalfa height less than 3 inches).
Sampling alfalfa stubble for potato leafhoppers.
A University of Illinois fact sheet contains a more detailed description of the biology, life cycle, and management tactics.--Mike Gray