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Eastern tent caterpillars

Eastern tent caterpillars inside and outside of silky nest.

Q • Can you tell me what is eating my cherry trees? There are these large white webs filled with worms and they are eating the leaves.

A • The Eastern tent caterpillar is the “worm” that spins the conspicuous white webs or “tents” on the branches of trees in the spring.

Tent caterpillars have a general preference for fruits and ornamental fruits, which would include your cherry, as well as plums, apples, crabapples and pears.

The caterpillars begin to hatch out in early spring from egg masses laid on the branches the previous summer and actively feed on the new leaves just as they start to grow. This occurs about the same time that saucer magnolias, wild plum and serviceberries are in bloom.

Their progress has been slowed somewhat this spring by cooler temperatures, but with the arrival of warmer weather their appetites increase as they grow in size. Emergence usually occurs over a two-to three-week period, and individual caterpillars then feed for four to six weeks.

When fully grown at about 2 inches in length, they stop feeding, spin a cocoon and pupate for several weeks before emerging again in summer as adults to mate and lay eggs. Pupal cocoons may be attached to the trunks of trees, but are also frequently affixed to the siding of a house or other structure near infested trees.

Even though defoliation sometimes occurs, healthy trees quickly recover with a flush of new foliage in a matter of weeks.

While still young and small, caterpillars tend not to venture too far from their webs. If these webs are located near the tips of branches, they can be easily pruned off. If they are located in in the crotch of a major limb and the trunk, to avoid removing too much of the tree they are best physically destroyed rather than being pruned off.

This can be easily accomplished with a stick, if you are squeamish about using your hand. Caterpillars return to the web at night, so evening is the best time to destroy the web. Find additional information and control options at tinyurl.com/dy9d62b.

The best way to control this pest is to keep it from hatching in the first place. Learn to recognize tent caterpillar egg masses.

These are dark brown, generally oval-shaped “collars” that encircle small twigs. They have a varnished appearance and are easily noticed all winter once the leaves fall off. They are the consistency of soft Styrofoam and can be simply peeled off the twigs with your thumbnail. Pruning the twigs is an alternative that is just as effective. On a small tree like a purple leaf sand cherry this is easily done from the ground or with the aid of a pole pruner. Place such prunings in the hot part of a compost pile or fold them tightly in a paper bag and discard them.

Write to Chip Tynan of the Missouri Botanical Garden at chip.tynan@mobot.org or Horticultural Answer Service, 4344 Shaw Boulevard, St. Louis, 63110.

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