The Bay Gardener

by Dr. Frank Gouin

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Don’t Let These Caterpillars Set Up Camp in Your Trees

Spray Eastern tent caterpillars with safe, organic Bt

It is very apparent that we will have a heavy infestation of Eastern tent caterpillars this year. You can already see an extensive distribution of nests on wild cherry and crab apple trees along roadsides in Southern Maryland. They are most visible in the crotches of branches near the tops of trees, especially near an asphalt roadway where they benefit from the reflected heat.

Don’t try to control these insects the old-fashioned method of burning them with oil-saturated rags at the end of a stick. This method is not only dangerous but also ineffective. Furthermore, the heat from the flame damages the bark of the trees, often causing a dieback of a large branch or treetop.

The best method of control is to use an organic Bt spray such as Thuracide or Dipel. Bt is a bacterium that is specific for such caterpillars and is safe to apply. It is the same spray used to control bagworms, cabbage looper and Gipsy moth. This spray is also approved for use by organic gardeners.

For maximum effectiveness, spray the foliage surrounding the web nest early in the morning or late in the evening. During daylight hours, the young caterpillars stay in their silk nests, which are impervious to water and sprays, but they emerge late evening or early morning to feed.

Generally a single thorough spraying of the foliage will produce excellent results. The longer you delay spraying the area surrounding the nest, the less effective the spray. Young caterpillars are more susceptible to Bt than mature caterpillars.

Bt sprays have a very limited shelf life. Purchase only what you will need for this year. Any container of Bt spray that is two or more years old is not likely to be very effective no matter how well it was stored.

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Tomato Planting Is Near

Q Each year I have planted my tomatoes in the same location in a raised bed. It’s the best and sunniest location in my yard, and in the past they have grown well. But the last two years they’ve developed some problems, including tiny beetle-like bugs.

I know I shouldn’t plant tomatoes in the same location year after year, but is there anything I can do to treat the soil or the tomatoes so that I can continue in this sunny spot?

–M.L. Faunce, Churchton

A The tiny beetles feeding on your tomatoes are most likely flea beetles, especially if they are making small pinholes in the foliage. They can be controlled by spraying every 10 to 14 days with the insecticide Sevin. If you are an organic gardener, you can try rotenone.

Yes, planting in the same location year after year causes soil problems. The accumulation of soil-borne diseases can be significantly reduced by spading a layer of one to two inches of fresh compost into the soil just prior to planting. The disease-suppressing properties of fresh compost will minimize the spread of those diseases. Also select tomato varieties that are disease resistant.