Potato leafhopper is common on a variety of trees and shrubs in at least southern and central Illinois. The feeding and associated injection of toxins at this time of year causes phenoxy herbicide-like (2,4-D) deformation of young leaves. Several pyrethroids, as well as other insecticides, provide control for at least 2 weeks. Scout before treating for the 1/8-inch-long, wedge-shaped, green insects on leaf undersides because it may be a month until the leafhoppers come back onto the trees after an insecticide application.
Bagworms have hatched throughout Illinois. In central and southern Illinois, the larvae will have fin-ished their ballooning by now so a single application of Bacillus thuringiensis kurstaki (Dipel, Thuricide), cyfluthrin (Tempo), or other pyrethroid should pro-vide control for the season. In northern Illinois, delay application until the week of July 7.
Periodical cicada males should be dying during the first week of July in northern Illinois. The singing will stop, and the dead males should be noticeable on the ground and sidewalks. This will also signal the beginning of heavy egg-laying of the females. Tree trunks up to 2 to 3 inches in diameter should be protected from egg-laying by loosely wrapping them with fine mesh such as fiberglass window screening or shade cloth. Leave this protection on the trunks until the end of July.
Arborvitae leafminer is a very small moth that lays its eggs on tips of arborvitae at this time of year. The hatching larvae tunnel into the scalelike leaves, causing them to turn whitish and then brown. These leaves can cause the entire tree to be less attractive, even from a distance. Application of abamectin (Avid), acephate (Orthene), or spinosad (Conserve) should provide control.
Larch sawfly larvae have also been found at the Morton Arboretum. The caterpillar-like larvae are powder green, with brown heads. They feed in groups, eating off the foliage. Handpicking and various chemical insecticides are effective control measures. Because this is not a caterpillar, Bacillus thuringiensis kurstaki is not effective.