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Scouting Watch

April 25, 2001

There are a number of early spring pests that you should be scouting for. Many appear on deciduous hosts as soon as leaves start to appear.

Eastern tent caterpillar appears as small, dark larvae grouped in silk tents in twig crotches when crabapple, wild cherry, hawthorn, and other host leaves are about half expanded. As larvae grow, they develop a broad, light stripe down the back and other markings but are dark overall. On cool or rainy days, they will be inside the silk tent and are removed when the tent is removed by hand or pruning. Bacillus thuringiensis kurstaki (B.t.k., Dipel, Thuricide) and other insecticides applied to the foliage are also effective.

Cankerworms hatch from eggs as leaves emerge on crabapple, honey locust, elm, hackberry, and other hosts. They have fewer prolegs than other caterpillars, causing a looping or inchworm-like movement. Attacked trees appear slow to leaf out because the larvae eat the leaves as they expand. Detect cankerworms by sharply striking the branch. This dislodges many of the green to brown larvae, and they will hang from the branch on silk threads. B.t.k. and other insec-ticides sprayed on the foliage control them.

European pine sawfly larvae appear early in the spring in groups on the needles of scotch, mugo, and other pines. They eat the second- and third-year needles but do not feed on the developing candle. Heavily attacked branches are not killed but have only a tuft of the current year’s needles at the end of the branch. Although the dark- and light-green striped larvae look like caterpillars, they are not. Therefore, B.t.k. (as noted) is not effective; but carbaryl (Sevin), acephate (Orthene), and other chemical insecticides provide control. Hand removal of larvae also works.

Hemlock rust mite, discussed in the mite article, has been found in northern Illinois by Don Orton, Illinois Department of Agriculture. Thus, they will be present throughout the state.

Northern pine weevil and Pales weevil can still be treated in northern Illinois with trunk drenches and seedling sprays of chlorpyrifos (Dursban). In central and southern Illinois, some control can still be obtained by spraying seedlings.

Author: Phil Nixon


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