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Fourlined Plant Bugs

Damage is easily mistaken for a plant disease

By: Sandy Feather 2011
Penn State Extension


Q. I started an herb garden last year and everything grew very well. This spring, I noticed that some of my plants had spots on the leaves. The spots have continued to get bigger, and it seems to be on more of the plants now. Can you tell me what is wrong and how I can save my plants?

A. The writer attached photos that show signs of classic damage from fourlined plant bugs  (Poecilocapsus lineatus) - circular brown to black spots about one-sixteenth of an inch in diameter. The spots often coalesce to create a more blotchy appearance that could easily be mistaken for some kind of disease. These insects move very rapidly and are often difficult to see. They are one of a few pests that injure a wide variety of plants, including herbs that are rarely bothered by anything else.

Other plants that often sustain damage from this pest include shasta daisies, Russian sage and blue-mist shrub, as well as the new growth of many shrubs, such as forsythia, deutzia, dogwood, and weigela.

Fourlined Plant Bug on a leaf
Fourlined Plant Bug
Photo: Sandy Feather

Fourlined plant bugs overwinter as eggs lain in the twigs of woody plants during the previous growing season. Females cut a slit in the new growth and lay their eggs while it is still tender. The eggs hatch in the following spring at about the same time as forsythia leaves begin to unfold. They generally feed on tender new growth with their piercing-sucking mouthparts. They extract the chlorophyll as they feed, and also inject a toxin, which results in the characteristic spots. Fourlined plant bugs feed for about six weeks in May and June. Adults die once they mate and lay eggs for next year's generation, so you will not see more damage from them until next year.

 


Fourlined Plant Bug Description

Adult fourlined plant bugs are yellowish-green with four black stripes. They are about one-quarter of an inch long. The smaller nymphs range from bright red to yellow. The black lines on the nymphs do not extend all the way down their bodies because their wing covers are not fully developed until they molt into adults. Both nymphs and adults create damage as they feed.


Damage

Although the damage they cause is unsightly, it is not generally life threatening to affected plants. On herbaceous plants such as herbs and perennial flowers, one of the easiest ways to deal with the damage is to wait until the pests have gone for the year, and then cut the plants back below the damage. They will regrow nicely, and you will never know how bad they looked in spring. This treatment can delay blooming of herbaceous perennials a bit, but removing the affected foliage improves the appearance of severely damaged plants.


Controls

If the damage really bothers you and you choose to spray, begin making applications at the first sign of their activity, because just a few of these pests can create a lot of damage. Also, nymphs are easier to control than the adults. Insecticides labeled to control fourlined plant bugs include insecticidal soap (nymphs only), neem oil, pyrethrins and piperonyl butoxide, a combination of rotenone and pyrethrins, and Sevin (carbaryl).

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