Answer: What you describe are most likely budworms. They are the larvae of moths. The moths lay their eggs on the unopened flower buds. The eggs hatch and the little worms bore their way into the unopened bud and feast on the petals. Then they exit, spin a little web to transport them to the soil where they pupate. There are several things you can do. Handpick the caterpillars you see or use the organic insecticide B.t. (Bacillus thuriengiensis) which is effective against caterpillars but is harmless to other insects, pets and humans. Bt is a bacterium which acts as a stomach poison so the caterpillars must continue to feed in order for it to be effective. Or you can use synthetic pyrethrins which are also effective. So, carefully inspect the unopened flower buds for evidence of eggs and wipe them off or hose them off. Then spray the unopened buds with Bt or a pyrethrin based insecticide. If you see caterpillars, hand pick them or spray them with Bt. Finally, be sure to cultivate the soil beneath the petunia plants to expose the pupating insects to the elements and to predacious insects and birds.
Best wishes with your petunias!
Q&A Library Searching Tips