Insect Quiz May, 2005

May Quiz 2005

You are working in your perennial garden when you notice the leaves of some of your plants have brownish spots on them.   You also notice some greenish beetle-like insects with black stripes .   Many of them appear to be feeding.   As you get closer to look, they move away quickly.

1. What are these insects?

These insects are fourlined plant bugs.   Although they may be confused as beetles, they are true bugs, possessing needle-like mouthparts and wings that crisscross and form an 'X' when folded.   When nymphs first hatch, they are red, later turning yellow and black.   As adults, they are 1/4 inch long with greenish-yellow bodies and four black stripes.   Fourlined plant bugs are first active in mid to late May and feed until early July.

2. On what kind of plants do they feed?

Both nymphs and adults commonly feed on many types of perennials, including chrysanthemum, mint, Russian sage, Chinese lantern, liatris, basil, and shasta daisy. They may also occasionally feed on annuals, like geraniums, and have even been known to attack fruits, trees and shrubs, although their damage is usually not noticed on these plants.

3. How injurious are these insects to plants?

As they insert their needle-like mouthparts into foliage, they produce round, tannish to black, sunken spots on the tops of leaves.   As feeding becomes more severe, leaf tips can wilt and curl.   Leaf tissue may even dry and fall out leaving holes in leaves.   Despite the appearance of injured plants, fourlined plant bug feeding is usually cosmetic, affecting only the plants' appearance.   The health of plants is typically not at risk.

4. What is the best management for these insects?

If you are only concerned about the health of your plants, then you can usually just ignore fourlined plant bug feeding.   If you wish to protect the plants' appearance, then early detection is important to minimize plant damage.   Inspect your perennials regularly, starting in about mid-May.   As soon as you notice feeding injury, treat your plants.   If you don't notice any damage until late June or July, it's too late to spray your perennials.

Common garden insecticides that are effective against fourlined plant bugs include products that contain the active ingredients cyfluthrin, esfenvalerate, permethrin, or carbaryl.   Treat as soon as you see feeding to prevent any additional plant damage.  

Unfortunately, there isn't a good solution for treating basil or other herbs.   You can spray these plants with insecticidal soap but it's not very effective on mobile insects like fourlined plant bugs.

** Read insecticide labels carefully to be sure that the plants you wish to spray are listed.   Do not treat any plants that aren't listed on the label.