Controlling Caterpillars on Petunias and Restoring Blooms

Tiny black grains on petunia flowers and leaves are likely caterpillar frass (droppings). Insecticidal soap won’t work. Use Spinosad (organic, e.g., Captain Jack’s Deadbug Brew), spraying in the evening to protect bees. It’s effective on a wide range of larvae.

To restore blooming: cut back about half the stems by half, water deeply, and apply liquid fertilizer. Petunias flower at stem tips, so pruning stimulates new flowering growth.