Issue No. 9, Article 6/May 21, 2004
First Potato Leafhoppers of the Year
The first sightings of potato leafhoppers have been reported this spring. Potato leafhoppers were found by Matt Montgomery, crop systems unit educator in Sangamon/Menard counties, and Dave Feltes, IPM educator for the Quad Cities Regional Center, in sweeps this past week. On May 12, Matt found 18 potato leafhoppers in 10 sweeps in alfalfa approximately 2 feet tall.
Potato leafhoppers do not overwinter in Illinois. They migrate north from the southern Gulf States, riding on northerly winds. Leafhoppers are small (1/8-inch-long), wedge-shaped insects with piercing and sucking mouthparts. Females live for approximately 1 month and during this time will lay two to three eggs in the stems and veins of plants each day. Nymphs hatch after 7 to 10 days and will mature to become adults in about 2 weeks. The entire cycle takes about 1 month, and three to four generations may be observed each year in Illinois.
Potato leafhopper and injury ("hopperburn").
While feeding, potato leafhoppers remove sap and fluid from vascular tissue from leaves, while injecting a toxic substance into the plant. This results in a yellowing of the foliage, typically beginning at the leaf margins, referred to as "hopperburn." An early symptom of hopperburn is the V-shaped yellow area on the leaf tip. However, don't confuse hopperburn with disease and nutritional disorders with similar leaf symptoms. Boron deficiency, which is quite similar to potato leafhopper injury, is usually limited to the younger leaves, whereas leafhopper injury is found on older leaves. Watch field margins for the first signs of potato leafhopper feeding as the insects move into the field.
Alfalfa fields should be monitored on a weekly basis following the first cutting of hay. Feeding on new regrowth may stunt or delay plant growth. 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.