Answer: There are several fungal diseases that result in black spots on sunflower leaves, as well as on other plants, and fungi love humidity! Sunflowers need drainage, so that may be weakening the plants' natural defenses further. You can try something to keep the disease from spreading, such as Silka-Ben (available from Gardener's Supply Co., http://www.gardeners.com, ph# 800-863-1700) or Shield-All Organic Fungicide from Gardens Alive (812-537-8650, email@example.com). Best of luck!
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