Key Features
- Skeletonized leaves
- Midvein remains
- White powdery larvae
Symptoms
Damage is done by worm-like larvae coated with stripes of white wax that consume the tissue between leaf veins. As larvae get bigger they can cut through thicker veins. Newly molted larvae lack wax, but become more waxy over time. Large larvae eat all but the midrib of the leaf. In August when large larvae are abundant, they can completely defoliate a plant. They are quite common on yellow and red-twig dogwood shrubs. Although defoliation is not likely to kill a plant it is unsightly and may predispose plants to diseases that attack stems.
Biology
Sawflies are stingless wasps that lay eggs into plant tissue using a saw-like tail. Adults emerge from their overwintering site to fly in late spring and lay eggs inside leaves that hatch from May to July. Worm-like larvae skeletonize leaf surfaces. Larvae can grow up to 1.5 inches long, shedding their skin 9 times in the course of a season. Early larvae are yellow and later larvae become dark green. Wax is laid on the larval skin after molting. In late summer larvae dig holes in rotting wood or loose soil to find a place where it will spend the winter in a transitional stage called a pupa. Often this will be moist wood from a porch or a deck.
Management Recommendations
Most effective control is achieved when pesticide is applied early in the season when sawflies are young and small. To control sawflies without promoting later season problems with scale insects use biorational products such as spinosad, chlorantranilioprole, indoxacarb, neem oil, insecticidal soap or horticultural oil. Insecticides are not effective after sawflies burrow into moist wood structures.
Effective Pesticides
Active Ingredients include: Acetamiprid, Bifenthrin, Carbaryl, Chlorantraniliprole, Horticultural oil (Paraffinic or superior oil) , Indoxacarb, Insecticidal soap (Potassium salt of fatty acid), Neem oil, Permethrin, Spinosad
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