Three Tips For Preventing Trunk Disease

Grapevines exhibiting Eutypa dieback. Common symptoms include stunted spring foliage. Photo: Allison Ferry-Abee

Grapevines exhibiting Eutypa dieback. Common symptoms include stunted spring foliage.
Photo: Allison Ferry-Abee

With proper control of trunk disease, a vineyard can last as long as 40 years. But trunk disease isn’t always a top priority among growers and PCAs.

“The problem with trunk diseases is that symptoms may not be seen until several years after the initial infection,” says Allison Ferry-Abee, University of California Cooperative Extension Advisor for Tulare and Kings counties. “This means that you probably won’t see the benefits of trunk disease prevention for two to 10 years (depending on the pathogen) after treatment.”

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Trunk disease typically comes in the form of Botryosphaeria dieback (bot canker), Eutypa dieback, and esca (black or Spanish measles). The symptoms of each of these are essentially the same: trunk cankers and vascular discoloration, and eventual vine death, Ferry-Abee says.

Disease spores are released during winter and early spring, often after rain or fog. These spores then infect wounds, including those from pruning. “From this point of infection, the fungus grows deeper into the vine,” Ferry-Abee explains. “It can infect spurs, cordons, and even the trunk.”

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She adds that the fungus can be slow to grow, which is why symptoms may not be visible until years after the initial infection occurs.

Here she offers a few tips for preventing trunk disease:

  1. Delay pruning. Prune in February, or as late as possible in the season. Because most rains in the Central Valley happen in early winter, delaying pruning helps avoid risk of infection during the heaviest time of spore release. “Wounds heal more quickly in spring than in winter,” she notes. “This reduces the amount of time wounds are susceptible to infection.”
  2. Double Pruning. If you’re not able to prune late in the season, consider double pruning, or making two pruning passes. In the first pass, pre-prune canes to 10 to 12 inches above spurs (for spur pruning) or to 24 inches above the cordon (for cane pruning). Ferry-Abee says the first pass should be done using a mechanical pruner. Canes should then be pruned to the desired spur or cane length in the second pass. “The goal of double pruning is to get the time-consuming part of pruning done when crews and/or equipment are available, and then get final, quick pruning tasks done when you will most effectively protect vines from disease,” she says.
  3. Protect pruning wounds. Check out the Grape Pest Management Guidelines for fungicides and protectants registered for use in California and apply them for trunk disease control during the dormant season. “Keep in mind that to effectively protect pruning wounds, you must spray vines from above rather than from the sides,” Ferry-Abee says. “The goal is to adequately protect as many pruning wounds as possible.”

What To Do If Vines Are Infected
While preventing trunk disease is your best bet, if vines are infected, it is possible to attempt to salvage them. Ferry-Abee recommends cutting off the infected sections of the vines until the dark, diseased tissue is no longer visible, including removing spurs, cordons, and portions of the trunk if necessary. “This isn’t always effective,” she notes. “It is possible for the disease to spread beyond visual trunk symptoms – but it is an option.”

She adds that it’s important to protect vines every year after planting. “Even if you’ve never protected your vines before, this winter is a good time to start,” she says.

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