Discourage disease by keeping dahlia foliage as dry as possible. Water deeply once or twice a week, allowing the top inch of soil to dry out in between. Clip off the bottom 12” of foliage to encourage good air circulation.
Slugs and snails love eating young dahlia foliage. Sluggo Plus is an effective organic control when it is applied early and refreshed often. Earwigs are another troublesome dahlia pest. Like slugs and snails, they prefer cool, moist conditions and can damage buds, flowers and foliage. Keep the area around your dahlias clear of spent flowers and foliage, and avoid using leaves or straw as mulch. This will give earwigs fewer places to hide and breed.