Pests to Watch for on Ornamental Trees and Shrubs

Eastern Tent Caterpillar.

Now is the time when we should first begin to notice the silvery-gray webs of the eastern tent caterpillar on apples, crab apples, wild plum, cherry and related trees. Larvae should be emerging from eggs that were laid on small twigs last summer by the female moths. These larvae gather at a major branch fork or crotch and begin to build the silk web or tent.

Eastern tent caterpillars feed on tree buds and foliage on warm sunny days. The remainder of the time is spent in the protective confines of the tent. As the caterpillars feed and grow, they enlarge the tents, making them more obvious in the landscape and along roadsides.

Damage can be reduced by removing and destroying tents and caterpillars as soon as they are noticed. Tent removal should be done in early morning or late evening or on cool rainy days when the caterpillars are occupying the tents. The caterpillars and the silk webbing are harmless to people; no harm comes from taking down the tent with your bare hands, although I understand some people would rather do this operation with a pole or gloved hands.

Foliage sprays of Bacillus thuringiensis can be used if necessary.

Pine Needle Scale Egg Hatch Should Happen Soon.

According to the phenological indicator system we use to predict when important events in the life cycle of insect pests will happen, the pine needle scale eggs should start to hatch soon. This common scale insect, found on pine and spruce trees, primarily spends the winter in the egg stage. The eggs hatch in early to mid-May and the tiny first instar nymphs, called crawlers, move about before settling to feed and develop in the same spot for the rest of their lives.

Because the crawler stage is vulnerable to insecticides, including soapy water and horticulture oil sprays as well as traditional insecticides such as diazinon, Orthene, malathion and Sevin, it is important to know when the eggs hatch. Close observational work done over the years has shown the pine needle scale egg hatch coincides with the bloom of Vanhouttei spirea, horse chestnut and Zabels honeysuckle. These events usually closely follow full bloom on common lilac, so now is the time to get ready to treat pines for scale if necessary.

This article originally appeared in the May 4, 1994 issue, p. 65.


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