Phomopsis and Phoma are wilt diseases on vinca groundcover
***It is no longer recommended to plant Vinca minor (Periwinkle or Vinca), especially near or adjacent to natural areas because it is an alien invasive plant.***
The usual symptoms on vinca include wilted shoots that darken and die with lesions near the base of the stem. The lesions are dark sunken areas on the stem near the soil line that enlarge and girdle the shoot. These fungal diseases attack through wounds, spread by water, and are favored by high levels of moisture. Stressed plants are also more prone to infection and dieback.
Avoid overhead irrigation and thin plantings to increase air circulation that will promote faster leaf drying. Thinning can be accomplished by selective pruning of infected leaves or by mechanical removal such as with a lawn mower set at the highest setting. Removal of fallen debris and clean up of old leaves etc. will also help reduce the amount of moisture trapped and will promote faster drying of the planting bed.