Botryosphaeria Canker

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Botryosphaeria canker (also known as bot canker and black dead arm) is known to occur in most viticulture regions of the world. In California, recent research has shown that over nine species of Botryosphaeria can infect grapevines and that the disease is prevalent in that state. The information on this page is based on information from California and other viticultural areas. 

However, the disease was found in B.C. during a 2007-2009 survey of grape decline problems by Agriculture and Agri-Food Canada.

Bot canker was detected in vines ranging from 3-11 years old in several vineyards. Two species of Botrytosphaeria were identified: B. parva and B. dothidea. The vineyards where B. parva was isolated showed severe decline problems. The disease had not been previously diagnosed in grapevine from B.C.

Symptoms

Botryosphaeria produces black streaks in the xylem of infected wood, typically causing wedge-shaped cankers in the trunk and cordons. The cankers are most easily seen when the vine is cut in cross section.

Black pycnidia (fungal fruiting bodies) form on diseased vine parts under the bark of cordons, trunks and spurs. Other diseases, including Eutypa canker, cause similar symptoms.

In California, botryosphaeria canker causes death of arms, cordons and vines, often so suddenly that there are no foliar symptoms. It is commonly seen in vines 10 or more years old. In other areas, foliar symptoms such as chlorosis and stunting are more common.

Symptoms may vary depending on the species of Botryosphaeria present. Typically, diseased vines fail to break dormancy or will suddenly wilt during the following growing season.

Spread

The fungus overwinters as pycnidia on diseased wood. Pycnidia release conidia (spores) when wet by rain or irrigation. Conidia are spread by water splash and wind, and cause new infections primarily through fresh pruning wounds. Moisture is needed for infection, along with temperatures above 5°C.

Botryosphaeria can also infect other tree species and could also be present in adjacent orchards, forests and riparian areas. The importance of spread from other host species to vineyards is not well understood.

Management

• Remove visible cankers and dead or declining arms, cordons and vines.
• Burn prunings from infected vines, or remove them from the vineyard.
• Prune healthy looking vines before pruning sick vines. Disinfect pruning tools periodically, particularly after pruning vines with symptoms.
• In California, late pruning during March results in less infection of pruning wounds. Optimal timing may be different in our climate. In general, warmer temperatures accelerate healing of pruning wounds, so wounds are susceptible for a shorter time.
• Pruning during a period of forecast dry weather would also help reduce infection.
• Good cultural practices help maintain vigour and reduce losses.
• There are no fungicide treatments for botryosphaeria canker available in Canada.