These articles are written to apply to the northeastern corner of Illinois. Problems and timing may not apply outside of this area.
Early Season Tree Insects
April 27, 2000
Insect pests can vary from year to year in numbers, but some make annual appearances. Two early season tree pests that show up every season to some degree are the eastern tent caterpillar and the European pine sawfly.
White, tent-like webs of eastern tent caterpillar may appear 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. Do not mistake this insect for gypsy moth that do not make webs in trees.
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 season tree insect to watch for is the European pine sawfly. If branches on mugo pine appear to move when you walk past, its 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 2000. Pines should only be pruned by cutting back the new candle growth, which typically appears in June.
Certainly there are many other insect pests that may appear during the season on trees and shrubs. But these two early species are almost a sure bet to show up somewhere in the area.