Jeffrey Hahn, Asst. Extension Entomologist
If you are out in your garden and notice small, uniformly sized spots on your favorite perennials, be suspicious of fourlined plants bugs. Fourlined plants bugs hatch in late May or early June and feed until early to mid July. Newly emerged nymphs are about 1/16th inch long and bright red. As they grow larger, they develop black wing pads which eventually develop yellow stripes. Eventually they mature into 1/4 - 1/3 inch long insects with a reddish orange head and greenish yellow wing covers with four black stripes.
Photo 1: Adult fourlined plant bugs. Jeff Hahn
Fourlined plant bugs feed on a wide variety of perennials, especially plants in the mint family. They are also known to feed on various shrubs. They use piercing-sucking mouthparts to feed on sap from the leaves which creates sunken, usually round spots. These lesions are of a similar size and are regularly distributed which helps to distinguish this damage from leaf spot diseases. Fourlined plant bug injury can also distort, cup, or curl leaves. This damage normally does not kill plants, but it can affect their appearance.
When managing fourlined plant bugs, it is important to discover their presence as early as possible to minimize injury to plants. If you are finding just a few fourlined plant bugs, you can just crush the insects. Otherwise, there are a variety of residual insecticides, including permethrin, bifenthrin, cyfluthrin, carbaryl, and malathion, that can be used reduce fourlined plant bug numbers.
Photo 2: Fourlined plant bug nymph and damage. Jeff Hahn