Usually, vineyards showing signs of canker disease have been infected by more than one type of pathogen. Growers have several options for controlling the diseases. “You want to minimize the risk of exposing pruning wounds to infection by spores,” Baumgartner explains

One method to delay pruning until late in the dormant season (February or March) when there’s less risk of rain and, thus, fewer spores. Also, pruning wounds made late in the dormant season can heal within about 10 to 14 days. That compares to December or January when such wounds can remain highly susceptible to infection for as long as four to six weeks until they heal.

 

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Another treatment, at least in the case of cordon-trained spur-pruned vines, is to combine mechanical pruning early in the dormant season with pruning the spurs by hand to two buds in late February or in March.

A third choice is to paint pruning wounds with a chemical protectant, such as Topsin or Rally, immediately after pruning.

A survey of grape growers, which Baumgartner’s team conducted at a series of meeting this past winter, found that the usage rate of treatments by these growers to prevent spread of grape vine canker disease varied from as low as 25 percent to as high as 80 percent, she reports. Delayed pruning was the most commonly used practice except in Sonoma County. There, the use of pruning wound protectants was the most preferred practice.

 Jonathan Kaplan, associate professor of economics at Sacramento State University, is one of the team members. He’s run the numbers comparing the effects on yields of treating vineyards for grape vine canker diseases at different times through his bio-economic models.

“We found that adopting preventive practices early, when disease infection rates in the vineyard are very low, produces returns that are very close to what you get in a healthy vineyard, less the costs of the practices themselves,” he says. “Also, we found, in most cases, returns improve when these practices are adopted. The exception is when you wait too long to start treatment, especially if the vineyard is 10 years or older. By then the infection level has become so high that the costs of the preventive practices outweigh any gains in yields.

This research is funded by a grant from the USDA Specialty Crop Research Initiative (The annual report is available online.)

 

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