Many gardeners have been encountering four-lined plant bugs on a wide variety of plants, especially perennials, such as chrysanthemums, Chinese lantern, Russian sage, mint, and wild geranium. They can also feed on shrubs, fruits, and vegetables. Immature four-lined plant bugs are bright red when they first hatch and gradually become darker as the black wing pads become larger. They eventually turn into yellowish greenish adults with four black stripes.
These insects use their piercing-sucking mouthparts to create small, sunken, dark-colored spots on the leaves. Heavily damaged leaves can become browned and misshapen. Despite the appearance, the injury is primarily cosmetic and the health of the plants is not typically impacted. It is possible that when plants are severely attacked a few years in a row, that their health can be affected.
|Fourlined plant bug nymphs on wild geranium. Note
dark colored necrotic spots on the leaves from their feeding.
Photo: Jeffrey Hahn, UMN Extension
There are several options for treating four-lined plant bugs. Insecticidal soap can be effective on nymphs but you have directly contact the insects to kill them. Insecticidal soap is not very effective on adults. Contact insecticides, such as permethrin, give good control; one application should be sufficient. When trying to treat these insects on basil and mint, try pyrethrins as they are usually broadly labeled to include herbs. However, like insecticidal soap, the spray has to directly contact the insects to be effective.
Four-lined plant bugs are active until early July so treating them now will still minimize feeding injury. For more information see Fourlined plant bugs in home gardens.