Botrytis blight causes the flowers to turn brown and decay especially in wet weather. A gray mold forms on the fading flowers. Pick off and destroy the infected flowers and spray with benomyl. Aster may infect marigold, particularly french and dwarf types.
Infected plants wilt and die.
Remove and destroy infected plants. No chemical control is listed A leaf spot causes oval to irregular, gray to black spots on the leaflets. The spots may be speckled with black fruiting bodies. The disease starts on the lower leaves and progresses upward. Varieties of african marigolds are most susceptible.