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Potato leafhopper adults and nymphs continue to infest alfalfa throughout the state. Many alfalfa fields in the state have required insecticide applications this year. Many other fields are exhibiting the wedge shaped yellowing of leaflets referred to as "hopper burn."

Potato leafhoppers are about 1/8-inch in length, wedge shaped, and greenish-yellow in color. They 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 which move in a northeast direction. The leafhoppers are thought to actively fly into the storms and be carried great distances by low level winds which approach 100 mph in speed. Leafhoppers are usually associated with strong thunderstorms containing hail. After a storm passes, high numbers of leafhoppers can often be found in the trail of the storms. In Missouri, the potato leafhopper adults generally arrive about 5 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 harvest. 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. This year potato leafhopper adults were found in alfalfa very early this year with adults arriving sometime during mid-April. 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.

Wayne Bailey
573 864-9905
BaileyW@missouri.edu