Answer: Based on your description it sounds like they are being attacked by sunflower stem weevils. These overwinter inside the base of the stems and then emerge in late spring or early summer to lay eggs and begin the cycle again. To stop the cycle, remove and destroy the old stems and roots (and thus the overwintering pests) of the sunflower plants each fall. You could also delay planting the new crop until June so that the new seedlings are too small to be attractive for egg laying purposes should any adults be in the area.
Q&A Library Searching Tips