Botryosphaeria canker (or often called as Bot canker) is the leading cause of grapevine cordon and trunk death in CA. Botryosphaeria spores can infect vines through pruning wounds, then cankers form near old pruning wounds and move down following the vascular system. A cross section of an infected vine reveals brown discoloration of vascular tissues, and advanced symptom often form a darkened wedge shape inside the woody tissue. Therefore, Bot canker is often indistinguishable from Eutypa dieback when only a cross section of the infected trunk is examined.. However, Eutypa dieback tends to show stunting of shoots and leaves, while Bot canker may cause water stress-type symptoms on green tissues. Bot canker symptoms generally show up on spurs, cordons and trunks of vines 10 years or older, leading to a slow decline of productivity and eventually result in vine loss. However, young vines, which is also susceptible to Bot cancer infection, can express rapid decline of an infected vine. Botryosphaeria may also cause Marcophoma rot on Muscadine grape clusters.
Causal Agents: Several Botryosphaeria spp.(B. australis, B. dothidea, B. lutea, B. obtusa, B. parva, B. rhodina, and B. stevensii.), cause cankers in older grapevines world wide, and may lead to major losses in vineyard productivity.
Management: The prevention at the time of winter pruning is the best approach for the management. Double pruning, protection of pruning wound using paint with boron (trade name: B-Lock), as well as chemical control, such as use of thiophanate-methyl (trade name: Topsin-M) and/or myclobutanil (trade name: Rally) to protect pruning wounds are known to reduce risk of infection to pruning wounds. Also, it is advised to prune vines on a day followed with several days of sunny condition. (I.e., avoid pruning before the rain) If you decided to use aforementioned fungicides, make sure to obtain the label for the specific uses. Although symptom appears in the vineyard after 5-10 years of planting, young vines are as susceptible as the old vines; therefore, it is advised to implement a management plan from early years of the vineyard.
For infected unproductive vines, remove infected trunk or cordon arm 12 inches below canker, and move the infected woods out from the vineyard for burying or burning. Vine health is extremely important for the recovery after the major pruning of cordon or trunk. Provide sufficient water and nutrients to encourage healthy vegetative growth.