Be on the lookout for potato leaf hoppers. They’ve been an increasing problem, due to more mild winters in the Mid-Atlantic and Northeast. Even if they didn’t show up at threshold numbers at first-cutting hay, they produce three to four generations each summer, points out Jerry Brust, Integrated Pest Management vegetable specialist at University of Maryland.

Leafhoppers are capable of very rapid population increases, so scouting is important to avoid crop damage to crops. Alfalfa, red clover and a few other forage legumes are the primary hosts. But PLH will move into other susceptible crops such as potatoes, raspberries and hops, warns Brust.

Hopper burn — yellowing of leaf margins — is the most obvious symptom. But once you see hopper burn, plants have already been damaged. Because of rapid population surges, it’s crucial to scout and control them before major damage can occur.

There’s no agreed upon threshold for leafhoppers in crops such as eggplant, raspberry or hops. But most recommendations have a threshold at two to three hoppers per leaf. Fields should be scouted weekly by checking the undersides of five to 10 leaves per 10 to 20 plants. If the average number of leafhoppers per leaf is at or above the threshold, then a control is needed.

Females lay two to four eggs per day in the leaf stems or veins of plants. In seven to 10 days, nymphs emerge. Nymphs undergo five instars and reach maturity in about two weeks. Newly emerged nymphs are nearly colorless with red spots that fade. Nymphs turn yellow, then change to pale green in the third and later instars.

Continue sampling in alfalfa
Bill Cissel, University of Delaware IPM specialist, advises weekly sampling of alfalfa for PLHs until final harvest. Ten sweep net samples should be taken in 10 random locations throughout the field when the alfalfa is dry. Treatment thresholds are based on alfalfa height:

• 3 inches or less: 20 leafhoppers per 100 sweeps
• 4 to 6 inches: 50 per 100 sweeps
• 7 to 10 inches: 100 per 100 sweeps;
• Greater than 11 inches: 150 per 100 sweeps

If the field is more than 60% bud stage or if it has experienced “hopper burn,” the alfalfa should be cut instead of sprayed.

Click on Potato leafhopper control in alfalfa for more ID information.

Source: University of Delaware