Last week, I mentioned that potato leafhoppers had been spotted in several counties across the state. Potato leafhoppers are small, pale-green insects that are "wedge shaped." Only about 1/8 inch long, these insects may cause quite a bit of damage. Potato leafhoppers migrate from southern states, arriving in Illinois during the spring. Females lay two or three eggs in the stems and veins of plants each day. Nymphs hatch after 7 to 10 days and mature in about 2 weeks. Three to four generations are observed each year in Illinois.
Potato leafhopper adult.
Injury caused by the potato leafhopper is due to its piercing and sucking activities. Fluids are removed from alfalfa plants, and toxic substances are injected into the vascular system. Symptoms of this injury, hopper burn, are identified by the yellow, V-shaped area at the leaf tip. Disease and nutritional deficiencies are similar to hopper burn, but these disorders generally begin at the leaf margins. Damage caused by leafhoppers may not become apparent for a few weeks. Consequently, symptoms will be found on older leaves. Severely injured plants also are stunted and bushy in appearance because the internodes stop growing normally.
Potato leafhoppers and injury ("hopperburn").
Alfalfa fields should be monitored on a weekly basis following the first cutting of hay. Using a 15-inch sweep net, make 20 sweeps in five locations of the field. Be sure to avoid sweeping wet fields; results are not necessarily representative of the damage potential of the field. Calculate a field average of potato leafhoppers per sweep. Randomly collect 20 alfalfa stems across the field to determine the average stem length. Table 1 provides the economic thresholds for potato leafhoppers. Potato leafhopper infestations will persist in fields until hard frosts occur in the fall.
Insecticides suggested for control of potato leafhoppers in alfalfa are listed in Table 2. Please follow all label directions and precautions.--Kelly Cook