AgWatch

Storms Bring Leafhoppers To Alfalfa Fields





Regrowth After Haying Most At Risk, MU Entomologist Says


COLUMBIA, MO.
    Farmers growing alfalfa should start scouting for the potato leafhopper, an insect that feeds on alfalfa, said Wayne Bailey, University of Missouri Extension entomologist.
   The insects, which are wedge-shaped, greenish- yellow in color and about one-eighth of an inch long, have been arriving in central Missouri since mid-May, he said. They feed on alfalfa juices, causing yellowing, stunted plant growth, or death of seedling alfalfa.
   Adults migrate into Missouri from southern states and Mexico, often in the wake of strong early-spring thunderstorms. “The leafhoppers are thought to actively fly into the storms, where they’re carried great distances by winds,” Bailey said.
   “Right now, they’re out there in moderate numbers and have potential to cause damage once alfalfa is cut,” he said. “Both forage quantity and quality are reduced by this pest.”
   Alfalfa regrowth on stubble recently cut for hay is at highest risk, as plants recovering from harvest can only tolerate one leafhopper per five net sweeps if the alfalfa is not a leafhopper-resistant variety.
   “The economic threshold for potato leafhopper in alfalfa depends on the height of the alfalfa and whether the alfalfa is a resistant or traditional variety,” Bailey said.
   “A traditional variety that’s 8 to 10 inches in height has a threshold of about one or more leafhoppers per sweep. A resistant variety can withstand three leafhoppers per sweep before treatment is justified. However, most farmers don’t have the resistant variety.”
   To detect potato leafhoppers, scout fields using a 15-inch diameter sweep net. Take 10 pendulum sweeps at five random locations in the field, Bailey said. Treat fields if the average number of potato leafhopper adults and nymphs per sweep reaches or exceeds the economic threshold.
   Farmers who start scouting now may prevent leafhopper damage, as recently arrived adults often feed initially on several tree species before moving to alfalfa fields, Bailey said.
   Damage can be caused by both adults and nymphs, which use their piercing-sucking mouthparts to suck out plant juices, he said. Δ

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