Psyllid sugar and potato/tomato psyllid nymphs are visible on the leaves of a tomato plant.

Psyllid sugar and potato/tomato psyllid nymphs are visible on the leaves of a tomato plant.

Ten years ago, new insect pest of tomatoes and potatoes was found in the Pacific Northwest. The insect is the potato/tomato psyllid (Bactericera cockerelli). Psyllids are small insects, about one-tenth of an inch long when fully grown.

Like aphids, they have piercing-sucking mouthparts that they use to suck fluids from the leaves and stems of potatoes and tomatoes. They can feed on other related plants such as peppers, eggplants, tomatillos and wild nightshade, but only potatoes and tomatoes appear to be injured. Potato/tomato psyllid excrement looks like granulated sugar, and collects on the leaves of infested plants. “Psyllid sugar” is often the first sign of an infestation.

The insect was first described in 1909 from specimens collected in Colorado, and was thought to occur mostly in Mexico, the southwestern United States and the Rocky Mountains. But in 2011 an outbreak occurred in the Pacific Northwest that caused substantial losses to the commercial potato crop. Potato/tomato psyllids damage plants by feeding on them, and also carry a bacterium that causes a potato disease called “zebra chip.”

Zebra chip damages potatoes and makes them unmarketable. The insect is best known as a potato pest, but infestations in home garden tomatoes have been reported in Chelan County in recent years. Infested plants may develop a condition called “psyllid yellows,” with discolored leaves and deformed growth. Tomato fruits may be dull-colored and lack flavor.

Entomologists once thought potato/tomato psyllids could not overwinter in the Pacific Northwest, but migrated annually from the south. However, they have recently been observed overwintering on climbing nightshade.

Adults resemble miniature cicadas. In late spring, females lay their eggs on the undersides of leaves. Eggs hatch in four to 15 days, depending on temperature. Newly hatched nymphs are pale brown or tan, becoming increasingly green as they develop. They become adults in two to three weeks, and can produce three to four generations in a season.

There are few tools available for controlling potato/tomato psyllid, as most pest control products have not been evaluated for this insect. Predatory bugs are important natural enemies of potato/tomato psyllid, especially damsel bugs and minute pirate bugs. Lady beetles and green lacewings will also feed on them, but are less important.

If you see potato/tomato psyllids in your garden, be cautious about using broad-spectrum insecticides. While these may kill psyllids, they also eliminate important natural predators and may increase populations of other damaging insects such as spider mites and leaf miners.

To reduce the chances of repeated infestation, remove debris from any tomatoes, potatoes or other plants in the Solanaceae family at the end of the growing season. Eliminate any nightshade growing in the area. Research on this insect is ongoing, and more information should be available soon.

A WSU Master Gardeners of Chelan County column appears weekly in The Wenatchee World. Connie Mehmel is one of four columnists featured. To learn more, visit wwrld.us/cdmg or call 667-6540.