Potato Leafhopper Numbers High in Some Alfalfa Fields

Published: July 27, 2009

Potato leafhopper adults greenishyellow in color, wedge shaped and about 1/8-inch in length. Adult leafhoppers are very mobile and quickly move sideways, jump, or fly when disturbed. This is a native insect which migrates into Missouri each spring from more southern states and Mexico. The potato leafhopper is often transported into the state by early spring storms, especially those that contain hail. Migrating leafhoppers are thought to actively fly into storm fronts and be carried great distances by low level winds (jets) which approach 100 mph in speed. After a storm passes, high numbers of leafhoppers often can be found in the trail of the storms. In Missouri, the potato leafhopper adults generally arrive in early May of each year. The arriving adults may feed initially on several tree species before moving to alfalfa to feed and reproduce. Two to three generations of potato leafhopper are often produced with economic damage generally occurring on alfalfa following removal of first and possible second harvests.

Damage is caused when both adult and nymphal (immature) leafhoppers use their piercing-sucking mouthparts to penetrate alfalfa leaflets and stems. They remove plant juices and often cause yellowing of established plants, stunted plant growth, and mortality of seedling alfalfa. Both forage quality and quantity are reduced by this alfalfa pest. Potato leafhoppers typically arrive in Missouri about May 5th each year, although their arrival in Missouri was delayed in 2009 with arrival in late May. Scouting is best accomplished using a 15-inch diameter sweep net. Take 10 pendulum sweeps at five random locations in the field. If the average number of potato leafhopper adult and nymphs per sweep reach or exceed the threshold numbers listed below, treatment is justified. The economic threshold for potato leafhopper in alfalfa depends on the height of the alfalfa and whether the alfalfa is a potato leafhopper resistant variety or a traditional alfalfa variety. Second and third cutting alfalfa crops are most at risk.