Leaf crumpler overwinters as a caterpillar in its damage on pyracantha, cotoneaster, crabapple, and hawthorn. Damage appears as several damaged leaves webbed together in a mass of frass-filled silk. Sprays of Bacillus thuringiensis kurstaki (Dipel, Thuricide), bifenthrin (Talstar), lambda-cyhalothrin (Scimitar), and other insecticides are effective when sprays are soaked into damaged areas.
Boxwood psyllid was heavy in several areas of Illinois last year. Damage appears as cupped leaves, particularly at branch tips, that later turn brownish. One method of control is to apply imidacloprid (Merit) to the soil so that this systemic insecticide is taken up into the plant. Application into the root zone with a soil needle may be the most effective method. Because Merit can take 2 months to circulate through the plant, application should be made now.
Japanese beetle can also be controlled with imidacloprid (Merit) as a soil application as described under boxwood psyllid. Due to the time required for circulation through trees and shrubs, this application should be made by the end of April. Research indicates that this application is effective in many situations, but expect spotty cases of little or no control.
As described in the book Coincide by Don Orton, saucer magnolia (Magnolia x soulangiana) is a major phenology plant during its bloom, which is occurring now or will soon occur in Illinois. Accordingly, the following insects should be scouted to verify treatment timing. Cooley spruce gall adelgid and eastern spruce gall adelgid can be controlled on spruce at this time in the northern half of Illinois. It will be too late once the galls form. Ash plant bug and pine sawfly should be present and treatable in southern Illinois and treatable in central Illinois in mid-April. Spring cankerworm and fall cankerworm will be present in all but northern Illinois, where hatch should occur in mid April. Refer to the 2003 Commercial Landscape & Turfgrass Pest Management Handbook for management suggestions. The book Coincide can be obtained from the publisher, Labor of Love Conservatory at (630)668-8597.