When it comes to detecting and treating vineyards for grapevine canker diseases (also called trunk diseases), like Botryosphaeria dieback (Bot canker), Esca, Eutypa dieback and Phomopsis dieback, the earlier the better, says plant pathologist Kendra Baumgartner, with the USDA’s Agricultural Research Service, based at the University of California, Davis. That’s why she’s leading a team of researchers and UC Cooperative Extension specialists and farm advisors to develop tools that will enable growers to do just that.

 

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These trunk diseases are triggered by rain splash which disperses fungal spores that enter the vine through wounds left by pruning or other injury. Typically, growers take action to control these disease once they begin seeing symptoms in the field. Usually, though, those signs aren’t apparent until the vines are about seven to eight years old. By then, the diseases may have been festering inside healthy-looking wood for several years, starting the vineyard on a slow, steady decline in grape yields and quality. While various treatment practices at this point can prevent infection of pruning wounds, they won’t eradicate wood cankers from already infected vines, which slowly succumb to the effects of the disease. Eventually, productivity drops to uneconomic levels.

Baumgartner’s team is working on field and laboratory techniques that would offer growers a simple, quick way to identify canker diseases on vines as young as, say, three years. It would involve placing traps in the vineyard to collect fungal spores following a rain event and sending them to a lab for analysis. Researchers currently use spore traps to study powdery mildew infections in vineyards. Baumgartner’s team is developing new, relatively easy-to-perform lab procedures for analyzing the ‘trap catches’ that would identify any disease spores within a day.

“Rather than having to wait until 20 percent to 25 percent of their vineyard is infected before they even know they have the disease, growers would be able to start treating their vines before the diseases get a good foothold,” she says.  “As a result, instead of having to pull out a diseased vineyard after just 15 or 20 years, the vineyard would remain productive for much longer.”

Delay pruning

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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