Description
The potato leafhopper (PLH) is a pest of alfalfa and dry edible beans. The adult is a pale green, wedge-shaped, winged insect about 3 mm long with piercing and sucking mouthparts. It is most broad towards the head, tapering evenly to the wing tips. It has a row of six rounded, white spots behind the head. Nymphs are smaller than adults, wingless, and often bright green in colour.
Life Cycle
PLH do not overwinter in Ontario but migrate north every spring, carried by weather fronts that start in the Gulf of Mexico. Adults may arrive in late spring, and may arrive in a field at threshold levels. Females lay their eggs in the tissue of main veins and petioles of leaves. Development from egg to adult takes approximately 4 weeks.
Damage
Potato leafhopper nymphs and adults suck juices from plant foliage, and in doing so they inject a protein that blocks plant vascular tissue. This causes the leaf edges to become yellow and puckered, with a characteristic yellow “V” shape beginning at the tip of the leaves. When severe, the leaves appear burned or necrotic, which is called “hopperburn”. Field border areas are usually affected first. Because yield is lost before hopperburn is evident, do not use the presence of hopperburn as a management guide. The symptoms of PLH are commonly confused with herbicide injury problems, nutrient deficiency and moisture stress during dry conditions.
Most of the damage occurs from June to mid-August. High-risk factors include hot, drier-than-normal seasons. Fields along Lake Erie tend to experience more frequent infestations. Leafhoppers tend to come into soybean and dry edible bean fields after neighbouring alfalfa fields are cut.
Scouting
The small size of PLH as well as their high mobility makes them difficult to spot in the field, but they can be found on upper and lower surfaces of leaves. Economic losses occur before plant symptoms develop, so it is important to identify the presence of large leafhopper populations before the damage occurs.
Scout in 10 areas of the field and check for PLH on newly and fully expanded trifoliates on 10 plants in each area, focusing on the center of the plant canopy. It is important to note that PLH adults readily fly away when disturbed, which makes them difficult to count on excised leaves.
Apply a foliar insecticide if the number of nymphs or adults per trifoliate has reached threshold as per the table below. A threshold has not been developed for scouting PLH in dry beans using a sweep net.
| Dry Bean Growth Stage | # of Adults or Nymphs per Trifoliate |
| Unifoliate | 0.2 |
| Second trifoliate | 0.5 |
| Fourth trifoliate | 1.0 |
| First bloom | 2.0 |
Management Strategies
- Insecticide seed treatments are recommended for this pest since populations can migrate from the southern U.S. via storm fronts and from neighbouring alfalfa fields at threshold levels. Once hopperburn symptoms are noticed, yield is already lost. Research conducted at the University of Guelph, Ridgetown Campus has shown that insecticide seed treatment can last at least 4–6 weeks after planting, eliminating the need for at least one foliar insecticide application.
- Consider using insecticide seed treatment on fields with a history of leafhopper infestations, to reduce the number of foliar applications required.
- Use foliar insecticides only if thresholds have been reached.
- A naturally occurring fungal pathogen helps reduce the populations of the PLH under warm, moist conditions. Predators and parasites appear to play a minor role in controlling the pest.
- If spraying during bloom, spray in the evening when bees are less active, and contact local beekeepers so they can protect their hives. Rotate insecticide chemical families to reduce the risk of resistance.
Dr. Art Schaafsma, University of Guelph, is acknowledged for his contribution to this information.
