Potato Leafhopper Can Damage Alfalfa

Potato Leafhopper Can Damage Alfalfa

Alfalfa growers should pay particular attention to potato leafhopper because it can be a serious pest in alfalfa, causing losses in both yield and quality. Knowledge of this pest and the degree it infests each field will help to control it and curb losses.

Know the Enemy

The adult potato leafhopper is yellowish-green, wedge-shaped, and approximately one-eighth inch long. The nymphs resemble adults but are wingless and more yellowish in color.

The potato leafhopper lives year round in the Gulf Coast region and disperses in the north each spring via weather fronts. The first adults can appear in late May or early June in the northern U.S., often arriving in the later stages of first crop alfalfa. Females may live a month or more and deposit two to three eggs a day within the stems, petioles, and major veins of leaves. The eggs hatch in about 10 days, after which the nymphs begin to feed.

Figure 1: Potato Leafhopper

Potato leafhopper nymphs will go through five stages and reach the adult stage in about two weeks. Several generations may occur during a single season and leafhoppers remain until the first killing frost.

Look for These Alfalfa Symptoms

The potato leafhopper has piercing-sucking mouth parts to penetrate plant tissue and remove sap. A toxin in the leafhopper saliva that is injected into the plant phloem during the feeding process causes a condition known as hopperburn. Wedge-shaped yellowing of leaf tips (see Figure 1) characterizes hopperburn. Hopperburn is sometimes confused with boron deficiency symptoms. However, hopperburn most likely appears on older leaves due to the delay in appearance; boron deficiency symptoms appear on younger leaves.

Heavy leafhopper infestations can stunt alfalfa and greatly reduce regrowth after cutting. Left unchecked, leafhopper damage may affect not only the current crop quality and yield, but the following season’s yield potential may also be reduced. The added stress of drought will further enhance the damage from potato leafhoppers.

Scout to Determine Level of Infestation

It is important to detect potato leafhopper infestations early before the visible symptoms are evident. Loss has already occurred when leaf yellowing is present. Begin scouting after the first cutting.

Potato leafhopper scouting is done with a sweep net sampling method. The standard sweep net has a 16-inch rim, a heavy muslin net and a three-foot handle. Insect sampling is generally done at five sites using an X pattern within a field and maintaining a minimum distance of 100 feet from the field border. The proper technique is to take 10 pendulum sweeps per sampling site and then stop to count the number of adult and nymph leafhoppers collected. Use this count to determine the average number of leafhoppers per sweep.

Table 1. Potato Leafhopper Economic Thresholds in Alfalfa

Stem Height (inches)	Average Number of Leafhoppers per Net Sweep
<3	0.2 adults
6	0.5 adults
8 to 10	1.0 adults
12 to 14	2.0 adults