Forest tent caterpillars

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(HOST) The great tent caterpillar invasion of 2005 may be over, but commentator Charlie Nardozzi says it’s likely that they’ll be back – and it’s a good idea to plan ahead.

(NARDOZZI) While traveling to Manchester, Vermont to give a talk this June, I happened to notice many trees on the hillsides with very sparse foliage. When I arrived at my talk, I discovered the cause of the damage. The forest tent caterpillar has been munch- ing its way around the southern and central parts of Vermont for a few years, and now they are being seen in northern regions, too.

These caterpillars can defoliate maple, ash, oak, aspen and other deciduous trees in no time. Although the damage probably won’t kill the tree, it will set it back. These hairy two-inch-long black caterpillars have blue stripes and white spots on their backs. Their population is cyclical. When weather conditions are right – cold winters with warm springs, such as we’ve had the last few years – the population builds.

Unlike the eastern tent caterpillar, the forest tent caterpillar doesn’t form an obvious white “tent” to protect its eggs. The forest tent caterpillar eggs are laid in distinct brown masses encircling branches and twigs. In spring, as leaves emerge, overwintering eggs hatch and the young larvae start eating. They’ll feed from May through June, pupate rolled up in the leaves and emerge in July to mate and lay eggs.

While most trees have leafed back out and recovered from the May and June defoliation, there are ways to reduce next year’s damage. You won’t be alone in fighting the caterpillars. If next spring turns cool and wet, caterpillar diseases may be your ally. Also, beneficial insects that prey on forest tent caterpillars are naturally building in numbers to feed on these pests.

In a large forested area, there’s not much a homeowner can do to reduce the damage. The State of Vermont has been aerial spray- ing certain hard-hit areas to reduce stress on trees. For an indivi- dual tree in your yard, especially short ones, you can look for the egg masses and destroy them this fall and winter. This will reduce the number of caterpillars for next year.

In spring, once the caterpillars emerge, spray Bacillus thurien- gensis (or BT) on the leaves. This biological poison is specifically targeted to members of the caterpillar family, so it won’t harm beneficial insects, animals or humans. As the caterpillars eat, they ingest the bacteria. This eventually kills them. Spray early to get the emerging caterpillars before they become a big problem.

As the cycles of nature turn, there will always be outbreaks of certain diseases, insects and pests. The key for home gardeners is to stay observant, gather information and then enact safe, res- ponsible controls to keep plants as healthy as possible.

This is Charlie Nardozzi checking his maple trees in Shelburne.

Related Link:
Forest Tent Caterpillar

Charlie Nardozzi is an all-around gardening expert with a special fondness for tomatoes and roses.

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