Leafhoppers

Several species of Empoasca leafhoppers occur in alfalfa. They all have the same general overall appearance: small [0.125 inch (3.2 mm) long], bright green, wedge-shaped bodies. Nymphs (immatures) also have green wedge-shaped bodies and run rapidly when disturbed. They may run forward, backward, or from side to side. Their curious movement plus their shape serve to distinguish them from lygus bug nymphs and slower moving aphids. Other green leafhoppers may be present in alfalfa, such as the threecornered alfalfa hopper, but they are much larger in size. Other small leafhoppers found in alfalfa are brown or gray in color and do no apparent damage.

The most common damage symptom is a yellow, wedge-shaped area at the tip of the leaf known as 'hopperburn'. Frequently, the leaf margin and tissue surrounding this area turns red. This symptom may occasionally be confused with boron deficiency but can easily be distinguished from it by the presence of the insects. Empoasca leafhoppers also inject a toxin into the plants, which can cause stunted plants with very short internodes. Stunting and yellowing may persist into the next cutting cycle, even in the absence of leafhoppers.

Although Empoasca leafhoppers may be found throughout the year, damage in the Central Valley is generally found during July, August, and occasionally September. In the Imperial Valley, damage may occur from May through September; infestations are often adjacent to or upwind from sugarbeets. Some years this insect is a major pest, other years it is not. Its cyclical nature may be associated with warmer winters where they overwinter in fields or they may be migrating in from other areas.

Scheduling an early cutting can effectively manage damaging leafhopper populations, otherwise insecticide treatment may be warranted.

If alfalfa is within a few days of harvest, early cutting will control Empoasca leafhoppers.

Only cultural controls are acceptable for use on an organically certified crop.

Check the field in July and August (and if necessary into September) to see if leafhoppers are present, especially for fields that are re-growing after harvest. At the first sign of injury, sample the field with a standard sweep net. For stubble fields, watch for damage when walking across the field, including: stunting of plants, poor regrowth, and high leafhopper numbers. Leafhopper infestations usually begin on the field margin so be sure to include field edges in your samples.

• Sample four areas over the entire field by taking five sweeps in each area and counting the number of adults and nymphs.
• Record observations on a monitoring form (PDF).
• If alfalfa is 2 or more weeks away from harvest: apply insecticides if counts reach five leafhoppers per sweep (adults and nymphs combined).
• If alfalfa is scheduled for harvest in 10 days to 2 weeks: apply insecticide if counts reach ten per sweep.

For information on sweep sampling, see the SAMPLING WITH A SWEEP NET section.

Leafhopper damage on stubble fields can be much more severe and the toxins they inject can stunt the plants, arresting growth and reducing yields. In these situations, threshold levels may be low. As a result, it is important to visually look at fields for the presence of leafhoppers and damage on newly cut stands. Often, leafhopper infestations with high enough numbers to justify treatment are confined to the first 50 to 100 feet of the field margin. If this is the case, apply insecticide only to the field edges where high leafhopper counts are found.