Approximately one week after second crop alfalfa has been cut, or by July 4, growers should start scouting the next crop for potato leafhopper, says Lisa Behnken, crops specialist with the University of Minnesota Extension Service. She has reported high levels of the insect in southeastern fields this season.

Growers need to act swiftly during the 30-day window between cuttings. They should scout for the pest with about one weekís worth of growth, sample to determine its population levels and then make treatment decisions.

If the population is below the treatment threshold, scout again in about a week. Insecticides vary from three to 14 days in their pre-harvest interval, the time between treatment and harvest. Behnken urges growers to choose one that fits their harvest schedule.

The potato leafhopper migrates into Minnesota each year via strong, southerly winds. How much harm the insect causes depends largely on weather conditions and wind patterns.

The potato leafhopper generally strikes alfalfa crops in southern Minnesota every year, due to wind patterns; however, it can be a serious pest in western Minnesota and North Dakota during some growing seasons.

The sampling method for potato leafhopper U experts and many entomologists recommend utilizes the sweep net. The grower sweeps the field in several locations, making 10 pendulum sweeps per location. The contents of the sweep net are then dumped into a plastic bag and sealed. The plastic bag is placed in the freezer for about an hour to slow the potato leafhopper. Then the insects are counted to determine the number of leafhoppers per individual sweep.

The U does not recommend treatment until a threshold level of 0.1 potato leafhoppers per one inch of alfalfa growth is reached, thus the threshold increases as the plant height increases. For example, if a grower has 10-inch alfalfa plants and counts one insect per sweep, the economic threshold has been reached.

Behnken says both adult and young (nymph) potato leafhoppers should be counted when using this sampling method.

What if a grower is getting very close to harvest and has already reached threshold? The U recommends cutting the crop a few days early. ìIt becomes a point of common sense when making that decision,î said Behnken.

Potato leafhoppers, very small, wedge-shaped insects, are bright green, quick-moving and have piercing mouthparts. When feeding, they cause alfalfa leaves to turn yellowish to reddish-yellow, crinkle and cup. Excessive feeding will lead to stunted plants and yield loss.

Source: Lisa Behnken, University of Minnesota Extension Service Regional Center, Rochester, (507) 280-2867