IPM

Managing Potato Leafhoppers

In Southwest Michigan Alfalfa Fields

Paw Paw, MI. Have you noticed alfalfa fields that have less than acceptable regrowth after the first cutting? Sometimes a lack of adequate soil moisture causes the problem, but if growing conditions have been favorable, the lack of growth may have been caused by leafhoppers. Potato leafhopper is an important pest of several Michigan crops, including alfalfa, dry beans, and potatoes. Damage from direct feeding is a result of not only adults, but also the tiny nymphs. What makes this pest especially dangerous is that early symptoms are very subtle and can easily be missed. Another concern is that once the leafhoppers arrive, they continue to feed and reproduce until killed by fall frosts.

Adult Leafhopper (actual size 1/8 inch)

(photo courtesy of North Central Region Extension Publication NCR547)

Identification

Adults: About 1/8-inch long, the adults are elongated with short, bristle-like antennae. They are lime green with translucent, greenish wings which are held at a roof-like angle over the body.

Eggs: The whitish, elongated eggs are about 1/24-inch long. Eggs are inserted in the plant stems and petioles.

Nymphs: The immature stages (nymphs) resemble the adults, but are wingless. When first hatched the nymphs are approximately 1/32-inch long. Nymphs are pale green and 1/8-inch long when fully grown. The potato leafhopper passes through five nymphal stages before becoming an adult.

Life Cycle

Potato leafhoppers overwinter in the Gulf states and migrate northward each spring on air currents. They usually arrive in Michigan during May or early June. Migration commonly occurs when a high pressure system east of Michigan and a low pressure system to the west combine to produce sustained flows of air to the north. These wind drafts can deposit adult leafhoppers on to Michigan crops virtually overnight. After arrival, adults locate forage crops for food and a place to lay eggs.

(diagram courtesy of MSUE Crop Advisory Team ALERT vol. 12, no. 2)

Adult potato leafhoppers readily fly or run sideways when disturbed, Females deposit one to six eggs daily on plant stems, leaf petioles, and leaf veins. The nymphs hatch in about 10 days. Like adults, they suck sap from leaf veins and run sideways when disturbed. Nymphs molt five times over a period of one to two weeks before maturing into winged adults. There may be several overlapping leafhopper generations per year in Michigan. By late June, leafhopper populations may increase sufficiently to damage hay crops. Leafhoppers will stay in crop fields until killed by fall frosts.

Damage

The feeding of both immature and adult leafhoppers is damaging to forage crops. Potato leafhoppers inject saliva into plants as they feed, resulting in abnormal cell growth and interference with transport of fluids in the leaves. A visible result of this damage is the characteristic "hopperburn," which is a wedge-shaped yellowish pattern on the tips of the leaves. Prior to this a slight yellowing or curling of leaves occurs, which is often overlooked.

Severely damaged plants are stunted and chlorotic. Leafhopper burn appears as yellow wedge-shaped areas on the tips of leaflets.

(photo courtesy of North Central Extension Publication NCR547)

Damage reduces forage yield and quality in several ways. Damaged plants may be stunted, with heavily infested fields experiencing as much as a 50% yield reduction. Damage also results in substantially lower protein levels. General stand vigor is decreased, leading to slow regrowth following cutting and increased winter kill.

Detection

Check alfalfa, clover, and trefoil fields for leafhoppers on the latter part of June or shortly after the first cutting, whichever comes first. A heavy duty sweep net should be used to properly sample for potato leafhoppers. Take 20 sweeps in five representative areas of the field and determine the average height of the crop at each location. Economic thresholds for alfalfa vary with crop height (see table below). In clover or trefoil, an insecticide application is recommended when there are one or more leafhoppers (adult or nymphs) per sweep of the net. If the infested crop is almost ready to cut, remove it first, check the regrowth and spray if needed. The potato leafhopper remains a threat throughout the season, so checks should continue until the final hay cutting is made.

Field use of sweep nets to determine economic thresholds

(photo courtesy of North Central Region Extension Publications NCR 586)

Management

Biological Control- A naturally occurring fungal pathogen helps reduce the populations of the potato leafhopper under cool, moist conditions. Predators and parasites appear to play only a minor role in regulating this pest.

Cultural Control- Cutting of forages is an effective method for reducing leafhopper damage. Adult leafhoppers will leave the fields when it is cut. The wingless nymphs will remain behind, but without foliage to feed on they quickly die. If a field is at or above threshold and is mature, cutting is the preferred control measure.

Resistant Varieties- There are alfalfa varieties on the market that are tolerant to leafhopper feeding or deter leafhopper feeding because of inflorescence (or leaf hairs) on the plant leaves. These varieties are currently being field tested by MSU in research trials.

Chemical Control- An insecticide treatment is justified when leafhoppers exceed thresholds and the crop is not yet mature enough for harvest. With systemic insecticides, 10 gallons of spray is sufficient for effective control. With non-systemic insecticides, a minimum of 10 gallons of spray per acre in small plants (less than about 6 inches tall) and 20 gallons per acre in taller plants should be a applied.

For further information on control of potato leafhoppers in Michigan refer to MSU Extension Bulletin E-1582 "Insect and Nematode Control in Field and Forage Crops" (updated annually).

Information in this document was adapted from MSU Extension Bulletin E-2270 "Managing Potato Leafhoppers in Forage Legumes", Doug Landis and Mike Haas, Department of Entomology and PRC, Michigan State University and "Potato Leafhopper Where Are They Now?", Christina DiFonzo, Department of Entomology, Michigan State University.

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Last modified: May 16, 1997