Potato leafhoppers have been detected in northern Illinois alfalfa fields. Yes, it has been very challenging to harvest alfalfa, but don't forget about this pest. These small, pale-green, wedge-shaped insects represent an important economic threat to alfalfa every year.

Potato leafhoppers are "brought" into Illinois each spring from southern states on wind currents. Depending upon temperatures during the summer, three to four generations occur each year. Typically, regrowth from cutting is most at risk for damage from the leafhoppers.

The insect has piercing and sucking mouthparts and hence remove fluids while injecting toxins into the alfalfa's vascular system. Plants that have been fed upon display the characteristic "hopper burn", a v-shaped yellowing at leaf tips. Once this symptom is seen, the damage has already been done.

Assessing leafhopper numbers and making subsequent management decisions requires the use of a 15-inch diameter sweep net. Insecticide application to conventional alfalfa (as compared to "leafhopper resistant" alfalfa) is justified at these combinations of alfalfa height and potato leafhoppers per sweep: under 3 inches, 0.2 leafhopper; 3 to 6 inches, 0.5 leafhopper; 6 to 12 inches, 1 leafhopper; and 12 inches or taller, 2 leafhoppers.

A University of Illinois fact sheet contains more details on the life cycle and management of potato leafhoppers; it is available at this web site http://ipm.illinois.edu/fieldcrops/insects/potato_leafhopper/index.html or from local Extension offices.