Flea weevils are being reported by the Morton Arboretum, and we are receiving calls of leaf tatter symptoms on Siberian elms elsewhere in the state. Because these insects overwinter as adults, control involves preventively spraying the emerging leaves in the spring with acephate (Orthene) or imidacloprid (Merit). These same insecticides should be effective at this time against the adult beetles, but much of the damage is already caused by the leafmining larvae.
The following is from the Morton Arboretum’s Plant Health Care Monitoring Report at http://www.mortonarb.org/plantinfo/plantclinic/phc/index.htm. The adults are 3-mm (1/8-inch)-long, gray–brown to black, oval beetles with a small, snoutlike mouthpart typical of weevils and enlarged hind legs used for jumping. The weevils eat one side of the leaf, leaving the thin epidermis intact. This feeding results in “window pane” symptoms on the leaf. Eventually, the epidermis dries out and pulls away, leaving 3-mm (1/8-inch), irregular holes in the leaves. Flea weevil damage can be differentiated from leaf tatter by the “window pane” symptoms and because the former occurs on newly emerging leaves and the leaf tatter is present on older leaves.