Time to Scout for Potato Leafhopper in Alfalfa Fields

Published: May 17, 2010

Around May 5 each year potato leafhopper adults generally migrate into Missouri. In most years these adults and their offspring will build in number and may severely damage alfalfa plants. Potato leafhopper adults are about 1/8-inch in length, wedge shaped, and greenishyellow 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 (jets) which approach 100 mph in speed. Arrival of leafhoppers is 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. The arriving adults may feed initially on several tree species before moving to alfalfa to feed and reproduce. Immature leafhoppers, called nymphs, look very similar to the adult stage except they possess wing pads instead of functional wings. Two to three generations of potato leafhopper are often produced each year 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, stunting of plant growth, and possible mortality of seedling alfalfa. Both forage quality and quantity are reduced by this alfalfa pest. Alfalfa plants damaged by potato leafhopper feeding will often turn yellow as sugars from photosynthesis are trapped in the plant foliage and cause the change in color to yellow, commonly referred to as "hopper burn". Scouting for this pest 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 leafhoppers per sweep (adult + nymphs) reach or exceed the economc 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. Most alfalfa varieties sold in Missouri in recent years are PLH resistant, although it is best to check the seed label. Alfalfa fields containing a companion grass are often less susceptible to potato leafhopper infestations than fields of pure-stand alfalfa.