Organic gardener faces webworm infestation


July 11, 1999

Q. My honey locust trees were covered last fall with brown webs filled with caterpillars. I think they are back again. What are they and what can I do about them? I'm an organic gardener and don't want to use chemicals.

A. Your trees are infested with mimosa webworm. The 1/2 -inch-long larvae feed on leaves under the protection of silken webs. You are witnessing the first generation, which will be followed by a second generation in late July and August.

If the webs aren't yet dense, you can spray the larvae with B.t., a microbial insecticide used by organic gardeners and farmers. Otherwise, try to prune out the large webs at the ends of branches or hit them with a hard water spray.

Q. I have very small, narrow black bugs all over my flower buds and open petals and on my raspberries. I've never seen such an infestation. What kind of insect am I dealing with? Will they be this bad all summer?

A. The pest is thrips, sucking pests that feed on foliage, buds, flowers and soft fruits. They seem to be especially bad this summer -- a result of drought. Infested flower buds and opened flowers turn brown, and their leaf undersides may appear dirty and silvery.

There are several generations of thrips each summer. Predatory insects will help keep their numbers down, but you can take steps yourself. Submerge your raspberries in cold water to wash the thrips off. Check for them by tapping foliage or buds over a piece of white paper and looking for small, quick-moving specks.

Q. I'm always on my guard against the squash vine borer, but now I have a new problem. They're big, ugly, brown bugs and they are trashing my plants. I've been dropping them into a jug of soapy water. Will I be looking at them all summer?

A. Your new nemesis is the squash bug. Luckily, there is only one generation each year. Adults over-winter and emerge in late spring, and the females lay clutches of dark-gold, oval-shaped eggs on leaf undersides and stems.

Continue to hand-pick the adults and find and squash the eggs to prevent a large-scale invasion. A note of caution: These are stink bugs; the adults emit a very unpleasant odor when threatened or squashed.


1. Check trees for the gauzy nests of the fall webworm. Prune out and discard any nests you find.

2. Control slugs in your garden by placing shallow containers of beer or a mixture of molasses, yeast and water around affected plants. Check traps daily and remove captured slugs.

3. Remove weeds from garden beds before they produce flowers and seeds.

Garden tips are provided by the Home and Garden Information Center of the Cooperative Extension Service of the University of Maryland. For additional information on these questions, or if you have questions of your own, call the center's hot line at 800-342-2507, or visit its Web site at

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