University of Illinois Extension
Bruce Spangeberg

These articles are written to apply to the northeastern corner of Illinois. Problems and timing may not apply outside of this area.

Stateline Yard & Garden

Sawflies and Tent Caterpillars Return

April 30, 1998

Spring has sprung in northern Illinois. As trees leaf out, insect pests cannot be far behind. Two of the early pests include Eastern tent caterpillar and pine sawfly.

Although not in huge numbers this year, the white, tent-like webs of eastern tent caterpillar have been appearing in crabapple, apple, cherry, and plum trees. This insect can be a serious problem since it may consume most or all of the foliage. Trees being defoliated so early in the season may become stressed. Recall from discussions in this column over the past few weeks this is not gypsy moth—which does not make webs.

If Eastern tent caterpillar appears on your trees, there are several control options. Perhaps the easiest is to carefully clip out the web and destroy it. Do this in the evening or on a cold, cloudy day when the caterpillars are inside. On sunny, warm days, they are out feeding.

Another control option would be to apply Bacillus thuringiensis (Dipel, Caterpillar Attack, etc.), which is a microbial insecticide that is very specific to the larva of butterflies and moths. Other types of insects, including beneficial insects, would not be harmed.

The second early insect to watch for is the European pine sawfly. If branches on mugo pine appear to move when you walk past, it’s probably a mass of European pine sawfly larva. They will feed on last year's needles, so will disfigure pines but most likely won't kill them. Mugo, Scots, and Red pine are among the favorite targets.

Control pine sawfly larva with carbaryl (Sevin) as soon as they appear. Instead of spraying insecticides, another possible option is to knock the larva off the branches with a stream of water or remove them by hand.

Don't cut off infested branches, as the terminal bud will be removed and new growth will not appear on that branch in 1998. Pines should only be pruned by cutting back the new candle growth, which typically appears in June.


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