Caterpillars

Look for large, irregular holes in rhododendron leaves from late spring through summer, particularly on Catawbiense and Pacific rhododendron. Multiple caterpillar species feed on these plants in the Puget Sound; cutworms and loopers are the most common culprits. You will see smooth, clean feeding damage rather than the notching produced by weevils. Many feed at night and hide during the day, so night inspections with a flashlight help confirm their presence before visible damage becomes severe.

Remove heavily infested leaves by hand or prune affected branches early in the growing season. Introduce or conserve parasitoid wasps and tachinid flies that naturally control many caterpillar species. Bacillus thuringiensis (Bt) applied when you see young caterpillars is effective without harming beneficial insects. Monitor new growth regularly; early detection prevents population buildup that might defoliate entire plants.