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Midwest alfalfa growers should scout for potato leafhoppers

Agriculture.com Staff 07/05/2006 @ 7:03am

Summer cold fronts and associated thunderstorms bring more than rain -- they can drop clouds of potato leafhoppers onto Midwest alfalfa fields.

"After the last two storm fronts, we started finding lots of adult leafhoppers," Wayne Bailey, a University of Missouri Extension entomologist, said last week.

Leafhoppers are carried on upper-level winds from Gulf Coast states where they overwinter in large numbers.

The adults and nymphs suck juice from the leaves and stems of alfalfa plants, leaving wedge-shaped injuries on the leaf tip. The leaves die and turn yellow, and heavily infested fields take on a yellow color as well.

The damage not only reduces hay yields for the current year, but also reduces stand vigor for the next year.

Newly seeded alfalfa fields and fields recently cut for hay are most vulnerable, Bailey said. A stubble field starting to grow again after hay harvest can be heavily damaged by a small infestation of leafhoppers.

The recommended economic threshhold for treatment is only 10 hoppers per 50 sweeps when a stand is less than three inches tall. For alfalfa 12 inches or taller, the threshold is 100 hoppers per 50 sweeps. Scouting sweeps are made with a 15-inch insect net.

"Alfalfa producers should be scouting their fields at least twice a week, especially after thunderstorms," Bailey said. "If high numbers of insects are found, an insecticide treatment should be considered," he said. However, if the alfalfa field is ready for a third cutting of hay, an insecticide treatment can be avoided.

"University of Missouri research shows that harvesting with a disk mower conditioner can reduce hopper nymph counts by 90%," Bailey said. "Fewer adult leafhoppers are killed by mechanical harvesters, as the hoppers jump out of the way."

Newer alfalfa varieties, with glandular hairs on their stems and leaves, are resistant to leafhoppers. "The hairs form a physical barrier which holds the hoppers away from the plant surface."

Learn more on the MU plant protection group's integrated pest management Web site at http://ipm.missouri.edu.

Photo: University of Minnesota IPM

Summer cold fronts and associated thunderstorms bring more than rain -- they can drop clouds of potato leafhoppers onto Midwest alfalfa fields.

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