It can kill individual stems or entire plants. Infection usually occurs between bud break and flowering when there is tender young tissue present, although new infections can occur throughout the growing season. This disease is favored by wet weather and temperatures between 50 o to 72 o F. Symptoms. The leaves on these stems turn reddish-chocolate brown and will remain attached to the branch. This sudden wilting is caused by one or several cankers completely encircling the stem.
Cankers are usually at the base of the plant, but can be a few feet aboveground.
By December they have turned red. This canker is usually centered around a leaf scar and often has a target pattern. As the canker grows, the center turns gray and dies, while the edges remain red. Tiny black dots, the fungal spore-producing structures, can be seen in the center of the older cankers. Prune out and destroy stems with cankers as these are the source of the spores.