Answer: You didn't mention whether or not the flower buds have holes in them. If so, you're dealing with a bud worm caterpillar and they typically hide on the undersides of the leaves so unless you carefully spray all plant parts, they will be difficult to control. Sometimes they can hide within the unopened flower bud and be protected from sprays. In any case, Bt (bacillus thuringensis, sold as Dipel) is a botanical which acts as a stomach poison. Caterpillars must consume the product in order for it to be effective, but it is a very efficient agent in controlling caterpillars.
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