Diseases Thielaviopsis, Pythium, and Rhizoctonia are most prevalent in Vinca when the plant is under stress, usually resulting from cool temperatures and overwatering. Pythium causes black lesions on the roots, and the medium has a musty smell. The best prevention for Black root rot is to maintain the proper growing conditions, especially proper temperature and medium pH, and pay careful attention to sanitation. The major garden disease of Vinca is aerial Phytophora. This disease is prevalent where overhead watering splashes soil and fungus spores onto lower foliage and stems.
Lesions develop on leaves and stems, killing the shoot but leaving a healthy root system.
The best preventative is to use drip irrigation. For information about obtaining these publications, contact your county Extension agent. For more information , contact your county Extension office. Look in your telephone directory under your county's name to find the number.