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Four-lined plant bugs are now active

Jeffrey Hahn, Extension Entomologist

If you have perennials in your garden, start monitoring for four-lined plant bugs now, especially if you have had problems with them in the past. These insects are bright red and 1/16th inch long when they first hatch. The immature nymphs and adults feed with piercing-sucking mouthparts which creates small, dark, circular, sunken spots on leaves. To determine whether these insects are present in your garden, watch for both four-lined plants bugs and their damage.
To the causal observer, these wild geraniums look pest free.
  Photo: Jeff Hahn, UMN Extension

Fortunately, while four-lined plant bug damage can affect the plant’s appearance, it normally does not seriously injure them. How much damage is deemed unacceptable is subjective and will vary with different gardeners.

Early detection is crucial for effective four-lined plant bug management. It is easy for gardeners to overlook the damage until it becomes too severe. Your goal should be to find the insects before they cause unacceptable damage. As you long as you do not find them feeding on your plants, you do not need to take any action. Even if you find that they are present, if only small numbers are present, it may not be necessary to treat them. You can also base your action on how severe their feeding has been in your garden in the past.

If you discover their presence, you have several options. Insecticidal soap, a low impact product,
However, when examined more closely, these same plants
reveal some minor feeding and a four-lined plant bug nymph.
Photo: Jeff Hahn, UMN Extension
would work reasonably well against the young nymphs but it is necessary to hit the insects directly. Insecticidal soap also does not have any residual activity so repeat applications will probably be necessary. Insecticidal soap is not very effective on older nymphs and adults. Pyrethrins, another insecticide without any residual, can be effective as long as you hit the insects directly. There are also a variety of residual insecticidal insecticides, such as permethrin, that can be sprayed to protect the appearance of the plants.

For more information, see Four-lined plant bugs in hone gardens.
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