- Botrytis: Petal spotting or petiole collapse from crown rot.
- Cylindrocarpon root, corm, and petiole rot (Cylindrocarpon sp.): Elliptical brown cankers at petiole base; brown discoloration inside corm; partial or entire wilting of plant. Remove infected plants. Sanitation is important.
- Fusarium wilt (Fusarium oxysporum f. sp. cyclaminis): Chlorosis of older leaves, followed by wilting and collapse of plants. Corm is firm but shows brown to purplish discoloration of vascular system when sliced open. Remove infested plants. Raise pH to 6.0, and avoid ammonium nitrogen fertilizers. Cultural controls to reduce wilt losses include using media with a pH of 6.0 or above, composted growing mix, and fertilizers low in ammoniacal nitrogen.
- Impatiens necrotic spot or tomato spotted wilt tospoviruses: Leaves may show round brown or black spots, “fingerprints” (ring spots of brown or yellow), or brown patches at the base of the leaf. Stems may show black bands. Control of the vector, the western flower thrips, is essential.
- Soft rot (Erwinia carotovora): Soft, mushy decay of corm leading to plant collapse. Control fungus gnats, and plant shallowly in a well-drained mix.