Answer: One of the most common pests of petunias is the budworm caterpillar. These small green worms appear in late June and July. You won't often see the worm itself. Instead, you'll see the droppings, which often are described as small black seeds. The worms feed on the flower buds, making small holes in the buds and the leaves.
These caterpillars are difficult to control but Bacillus thuringensis (B.T.) and Bifenthrin are reasonably effective insecticides. If left unchecked, the presence of the caterpillars will cause petunias to stop blooming.
You have the timing just right - start treating your plants in late June and you should be able to get ahead of the worms. As for the aphids, they're interested in the plants because of the sticky fluid that the plants are exuding after being attacked by the budworms. If you can get the budworms under control, the aphids won't be quite so interested in your petunias.
Better luck next year!
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