Gypsy moth eggs have been hatching in northern Illinois. The Illinois Department of Agriculture (IDOA) and USDA APHIS will treat for the larvae toward the end of the month. Oaks, major hosts for gypsy moth, break bud relatively late. Waiting until oak leaves are half expanded provides additional surface area, result-ing in better control. Where gypsy moth is numerous--as in Lake, Cook, DuPage, and McHenry counties --application can be made by arborists, landscapers, and others. In counties other than Lake, check to be sure that you and IDOA are not treating the same trees. Bacillus thuringiensis kurstaki (Dipel, Thuricide, others), spinosad (Conserve), tebufenozide (Mimic), diflubenzuron (Dimilin), and cyfluthrin (Tempo) are all very effective against the caterpillars.

Whitemarked tussock moth is hatching and can be treated in southern and central Illinois. It commonly feeds on crabapple, oak, linden, maple, and sycamore. Bacillus thuringiensis kurstaki (Dipel, Thuricide, others), spinosad (Conserve), and several other insecticides are very effective.

Maple petiole borer damage has been reported from Effingham County in southeastern Illinois. The borer is a sawfly that lays its eggs at the base of the leaf petiole in the spring. The resulting larvae tunnel through the petiole, causing the leaf blade to fall off close to where it joins the petiole. The larva remains in the petiole that stays on the tree. Later, the petiole drops to the ground, where the larva pupates. There is one generation per year. Although this insect’s damage is impressive--with up to 30% of the leaves without petioles falling from the tree in May and June--it typically has no serious impact on the tree, and there is no control. As the larva is not in the fallen leaves, raking and destroying the leaves has no effect.

Birch and alder leafminers are treatable at this time in central and southern Illinois and will be treatable in a week or so in northern Illinois. Typically, these and most other leafminers are not numerous enough to warrant treatment, and plants seem to do well in spite of them. It is common for birch leaf-miners to be in numbers high enough to warrant treatment in the northernmost row of Illinois counties. If these leafminers are very numerous, acephate (Orthene) or imidacloprid (Merit) should be effective.

Scale crawlers of several species are present at this time and treatable. Before treating, check to make sure that the crawlers are out. They are period-sized insects moving around on the leaves and branches. Double-sticky tape wrapped around a branch captures the crawlers, making it easier to scout for them.

Scurfy scale appears to be more common recently in Illinois. This white scale is on the trunk and branches of crabapple, maple, alder, hickory, ash, willow, and many other trees. Its purplish red crawlers are treatable now. Heavy infestations kill the tree. Pine needle scale should be treatable as brick red crawlers around the state. Euonymous scale (bright yellow crawlers) and oystershell scale (gray crawlers) are treatable in central and southern Illinois and should be out as crawlers in northern Illinois later in May. Most contact insecticides are effective against scale crawlers, including insecticidal soap, summer spray oil, and pyrethroid.