Dusky Birch Sawfly Larvae: Not Caterpillars, Need Different Treatment

Identifying and Controlling Dusky Birch Sawfly

The larvae defoliating your 'Whitespire' birch look like caterpillars but are actually the larvae of a sawfly (a wasp relative). This distinction matters because Bacillus thuringiensis (Bt) only works on true caterpillars.

Effective Controls

• Carbaryl (contact insecticide) sprayed on the entire canopy.
• Imidacloprid (systemic) applied as a soil drench before feeding begins.

Monitor in late summer; early intervention prevents severe defoliation. Though the tree refoliates next spring, repeated attacks weaken it over time.