Columns, In the Garden

Watch Out for These Two Pests

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BURLINGTON – Many gardeners are reporting damage lately from two pests, the fourlined plant bug and slugs. The plant bug causes minor cosmetic damage, but slugs can be quite destructive if left unchecked.

photo by Ben Pomykala
Sunken brown angular leaf spots on sage and other host plants are caused by adult fourlined plant bugs feeding on the foliage.

The fourlined plant bug (Poecilocapus lineatus) feeds on mint, basil, sage and Shasta daisies. This little insect causes sunken brown angular leaf spots that resemble disease symptoms.

The insects hatch in the spring, and the nymphs, or larval stage, are bright red with black wing pads and black dots on their abdomen. As the nymphs grow, they become reddish orange with larger wing pads with a light-colored stripe on each pad.

The adults are about 1/4-inch long and greenish yellow with four black stripes running down the wings. Their heads are orange-brown, and their legs are yellow-green. Both life stages have piercing sucking mouthparts and can cause this leaf-spotting damage.

These pests do damage and do not sit still for very long. Usually, the damage is cosmetic, and row covers will protect important plants.

photo by Ann Hazelrigg
Slugs feed on a wide variety of host plants, leaving irregular-shaped holes on foliage and flowers, such as the damage found on this zinnia.

Slug populations and damage are high this season due to all the wet weather last summer. Slugs can vary in color and are basically snails without shells. Their heads have two pairs of feelers, one pair that carries the eyes and one pair that is used for smelling. They can range in size from1/4-inch to eight inches or more.

Slugs lack legs but produce slime to help them glide. You can often see dried slime trails that indicate slugs are active. They are present in cool, moist areas with shade throughout the growing season.

They feed on lots of different hosts and can be especially destructive on seedlings and ripening fruits and vegetables causing irregular-shaped holes and rasping damage. Hostas are a favorite food, but they seem to prefer certain cultivars over others.

Slugs are reduced by a variety of methods. Modify their habitat by pruning and thinning trees and perennials to let in more sunlight and allow the soil to dry out.

Remove containers, boards, pavers and flat stones where slugs tend to hide. Don’t over mulch or leave plant refuse on the ground.

Choose plants and cultivars that slugs do not prefer. Set out slug traps like boards or cardboard to collect and handpick the pests. There are also organic slug baits that can be used as a last resort.

Dr. Ann Hazelrigg is the University of Vermont Extension plant pathologist and director of the UVM Plant Diagnostic Clinic.

Ann Hazelrigg

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