A University California study in 2001 estimated the annual cost to growers, statewide, from trunk disease, including the value of lost production, treating the disease, retraining new cordons and trunks and replacing vines, at $260 million.

“That study involved just one of the pathogens,” Gubler says. “But we now know more than one pathogen was causing damage.

"The only way to eliminate trunk disease from a vineyard is to prune out infected wood and ensure that no cankers have developed below that area," he notes. Otherwise, the pathogen will continue to grow.

“As soon as you see diseased wood, prune it out immediately and retrain new cordons,” Gubler says “The longer you leave the disease in your vineyard, the harder it becomes to prune it out, and you run the potential of increasing inoculum.

“In a severe case with cankers moving down the trunk, train up suckers from scion material and let it grow during the summer. Then, prune the diseased wood out in the winter and retrain the suckers for a new vine.”

The best way to prevent trunk diseases is to prune as late in dormancy as possible and treat each wound with a protectant, he says. Late pruning takes advantage of more heat units in early spring which speeds up the healing process.

University of California research shows that wounds created in late-dormancy pruning are about 90 percent less susceptible to trunk disease than those pruned in December or January, Gubler reports.

He’s also studied an option for pruning earlier in the dormant period by using a rotary saw to leave five to seven bud position spurs and then coming back in late February or early March to prune the vine back to two buds. Vines inoculated with Eutypa and Botryosphaeria in late February or early March had about 95 percent fewer cankers than those inoculated in December or January.

In addition to treating infected vines with Topsin M or Rally fungicides, several wound protectants are available that offer longer protection. The fungicides are effective for about two weeks. So they must be re-applied depending on rainfall events because wounds can remain susceptible to infection for eight to 12 weeks. “This short term protection is why we asked for Rally and Topsin M to be registered for tractor application,” Gubler says.

One of these wound protectants, VitiSeal, is an acrylic paint. It was introduced in the past few years. Containing three essential oils, it can be hand-painted or sprayed on vines to provide about three months of protection. “So far, it has worked well in our trials,” Gubler says.

Gubler is also testing Spurshield, another wound protectant, introduced this past winter.

“These products are more expensive but I think growers should look at this as the cost of either spending the money for protection or for vine surgery and retraining the vineyard.”