Battling the leafhopper blues

Leafhoppers are not common pests in the greenhouse, but because they can plague production of outdoor-grown herbaceous perennials, they can be found as invaders from the outdoors trapped on yellow sticky cards. Of the more than 2,500 species of leafhoppers found in North America, growers are most likely to encounter just a few species: potato, aster and mint (also known as sage) leafhoppers.

Adult leafhoppers are small insects (about 1/8 to 3/16 of an inch long) with slender, wedge-shaped bodies that taper at the end. With piercing-sucking mouthparts, leafhoppers feed on plant sap, causing pale spotting or distortion of leaves, yellowing, stunting and loss of plant vigor.

Potato leafhopper
The potato leafhopper is found primarily in eastern North America. Feeding causes leaves to develop yellow and brown margins, which is known as ‘hopperburn,’ and growth may become stunted. This damage is sometimes mistaken for fertilizer (or high soluble salts), drought or herbicide damage. Look for the pale green nymphs with their characteristic crab-like walk, especially on Alcea, Astible, Baptisa, Dahlia, Gaura, Hibiscus, Lupinu, and Nepeta.

Very active leafhoppers dart around and fly up from foliage when disturbed, so using yellow sticky cards is helpful. Using yellow sticky cards also makes it easier to determine which species of leafhopper is present. Potato leafhopper adults are approximately 1/8-inch long and light green with six characteristic white spots just behind their head that are visible under high magnification. This species overwinters only in the warmer parts of the southeastern United States, migrating northwards annually. There may be three to five generations per year in the Midwestern states. Consult your local extension’s vegetable crops IPM or pest alert messages to learn when leafhoppers arrive in your area and establish infestations in commercial potato and bean fields. You know then to start looking for leafhoppers on your ornamentals.

Aster leafhoppers
Adult aster leafhoppers are about 1/8-inch long and yellow-green, with six black spots just behind the head. Use sticky cards to trap adults in order to see the distinguishing spots behind the head. Aster leafhoppers overwinter as an egg on various grasses and perennials. In southern Ontario, there can be up to five generations during the growing season.

Aster leafhoppers transmit the pathogen that causes aster yellows disease; insects migrating in from southern states are especially known for this. Aster yellows may be found on herbaceous perennials, annuals, cut flowers, vegetables and weeds. Members of the aster family (Coreopsis and Echinacea) are commonly affected. Plants infected early in the season become stunted, with shortened internodes and deformed yellowish-green flower heads. Severely infected plants develop a bushy mass of leaves (known as a “witches’ broom”) with no normal flower production. Infected plants cannot be cured. Manage weeds in and around production areas to prevent infection of alternative hosts and overwintering of aster yellows.
 

Sage leafhopper
The sage (also known as mint) leafhopper prefers herbs in the mint family, such as rosemary, sage, catnip, spearmint, lavender and oregano. Native to Europe, this insect is now established around the United States and has been a pest both outdoors and in greenhouses. Adults are small (slightly larger than 1/8 inch) and pale with distinctive brownish oval markings. Feeding damage may be confused with leaf injury caused by thrips, lacebugs or spider mites, and young leaves may become distorted.

Leafhoppers are notoriously difficult to control because they are so active and mobile. In some cases, the source of infestation may be outside the greenhouse or production area. Potato leafhopper is particularly notorious for repeated waves of migrating insects moving into crop areas. In such cases, using just contact insecticides has limited efficacy, since new leafhoppers can enter an area after sprays have dried. Systemic or other residual insecticides may be necessary to prevent feeding damage.

Leafhoppers’ natural enemies include general predators such as lady beetles, lacewings, spiders and nabid bugs. Unfortunately, these enemies usually do not provide adequate control in such situations. Microscreening can also help keep leafhoppers out of greenhouse production and propagation areas.

Pundt is an extension educator at the University of Connecticut and a frequent contributor to Greenhouse Management. Have a question? Reach her at leanne.pundt@uconn.edu.