Continue to watch for cankerworms, eastern tent caterpillar, European pine sawfly, and spruce spider mite. Cankerworms can be scouted by forcefully striking branches of crabapple, elm, honey locust, hackberry, and other host trees. The caterpillars will drop off and hang below the branch on silk threads. Eastern tent caterpillar is easily identified by its silk tents in the twig crotches of crabapple, hawthorn, mountainash, and other hosts.
Watch for European pine sawfly and spruce spider mite on needled evergreens. European pine sawfly occurs as groups of greenish caterpillar-like insects with black heads on scotch, mugo, and other pines. Spruce spider mite and other mites that feed on needle evergreens can be scouted by forcefully striking branches above a sheet of white paper and then looking for signs of the tiny, crawling mites. Slow-moving mites that make green streaks when they are smashed are usually pest mites; fast-moving mites that make red streaks are likely to be beneficial predatory mites.
Honeylocust plant bugs and ash plant bugs are present in northeastern Illinois. It usually takes one to two honeylocust plant bugs per compound leaf to result in damage. At that level, you should be able to see several of the pinhead-sized green bugs running across a cluster of leaves when they are disturbed. Ash plant bugs will cause numerous light spots or stippling on the leaflets, which may turn brown later in the year. This pest is usually not treated unless the tree is located in an obvious part of the landscape and has low limbs where the damage will be easily noticed. Consult the Illinois Commercial Landscape and Turfgrass Pest Management Handbook, 1998–1999 for control recommendations.