- Septoria leaf spot: Angular leaf spots, brown to purple in color.
- Foliar nematode: Angular leaf spots, which are easily mistaken for a fungal disease.
- Ovulinia petal blight: Brown discolored areas on flowers, beginning as tiny, water-soaked, round spots and progressing to flower collapse. More aggressive than Botrytis but could be mistaken for Botrytis flower blight.
- Rhizoctonia stem rot: Cankers form at soil line; particularly likely during propagation.
- Phytophthora root rot and wilt or branch dieback: A highly contagious and aggressive disease. Young shoots that are directly invaded wilt, eventually turn brown, and die. If infection is through the roots or crown (as is more common in New York), roots are softened and brown and/or a reddish-brown canker develops at the soil line. All or part of the plant eventually wilts and dies. A reddish-brown canker or vertical streak may be evident just beneath the bark on the lower stem.
- Cylindrocladium blight: May cause purple or brown leaf spots, as well as lethal root rot or cutting rot. Affected stem tissues turn reddish brown in the cankered areas. High moisture and temperatures of 27–29°C (80–85°F) are very conducive to disease.