I manned the University of Minnesota tent at Farm Fest and answered questions from farmers and gardeners across Minnesota. In addition to numerous gripes about Japanese beetles, I talked to a few farmers in southeastern Minnesota who have found potato leafhoppers (Empoasca fabae) in their alfalfa fields. Late June through August is usually when we see them in Minnesota, after they migrate up from southern states.
Potato leafhoppers are true bugs, in the same insect order as aphids. Adults are lime green and about 1/8 inch long. Their bodies are slender and wedge-shaped with heads that are slightly wider than the rest of their bodies. As true bugs, leafhoppers undergo incomplete metamorphosis, meaning that the immature leafhoppers are called nymphs and look similar to the adults except for being smaller, paler, and wingless.
Potato leafhopper adults and nymphs are both very active. The adults jump or fly away as you walk through the field. If you disturb the nymphs, they move very quickly in a distinctive sideways movement across the leaf in an effort to hide on the underside of the leaf. Nymphs feed mostly on the underside of the leaf and are considered even more damaging than adults.
Being true bugs, potato leafhoppers have piercing-sucking mouthparts which they use to feed on the water and nutrient conducting tissue of plants. They also inject their saliva which causes physical damage that plugs the vascular tissue. The first signs of damage are leaf veins turning pale and leaves beginning to curl. Sometimes, yellowing appears in a v-shape at the tip of the leaf, which is referred to as “hopperburn.” Their damage can ultimately lead to stunted growth. A word of warning that curled, chlorotic foliage may also be a symptom of a nutrient deficiency. Therefore, correct identification of the culprit is important for making management decisions.
Potato leafhoppers should be monitored after the first cutting through the end of the season. A sweep net is the most effective way to sample for potato leafhoppers because adults and nymphs are extremely active and easily disturbed. You can find scouting techniques and thresholds on our University of Minnesota Extension website.
Healthy alfalfa stands are able to tolerate some potato leafhopper feeding. An ideal strategy for protecting alfalfa from potato leafhopper involves multiple approaches. Adults are repelled by plant hairs, and nymphs get caught in the sticky hairs and starve. Therefore, glandular-haired alfalfa varieties can significantly reduce yield losses. Additionally, timely cutting will force adults to move to nearby crops, but they often move back into a field after regrowth occurs. It is important to scout seven to ten days after each cutting to monitor for possible reinfestations.
In conjunction with the other two approaches, insecticide applications can protect alfalfa yield from potato leafhoppers and are economically justified with regular scouting and the use of economic thresholds. The variable values of hay and control costs are important considerations for making a treatment decision. Thresholds and values can be found on our Extension website.