Eutypa was once considered the primary culprit in California grapevine cordon and trunk diseases. However, researchers have confirmed that Botryosphaeria (commonly referred to as Bot Canker) closely mimics the symptoms of Eutypa and is a significant concern. Symptoms include dieback, dead-arm, blockage of the vascular system, and yield loss.
The V-shape cankers caused by Botryosphaeria are virtually identical to those formed by Eutypa lata or the newer identified species — Eutypa leptoplaca.
“We're fairly certain that over the past 35 years all of these species have been producing cankers in vines,” says Doug Gubler, plant pathologist with UC Davis who was addressing attendees at the first stop of UC's Central Coast Research Roadshow in Paso Robles, Calif. “The Botryosphaeria group of fungi has largely been overlooked as grape pathogens. They have been considered to be saprophytes or at least weak pathogens on grapes. In the past if we isolated Botryosphaeria in our research, we would just toss them out.”
More recent research, however, has shown that these fungi produce a broad range of effects on grape vines that can be potentially severe. Those symptoms vary depending on the species of Botryosphaeria, but may include shortened internodes, bud necrosis, vascular necrosis, chlorosis of leaves, vein dieback, trunk dieback, cane bleaching, dead- arm, and absence of spring growth.
“Absence of spring growth is the primary symptom we see in California,” Gubler says. “If you go out to the vineyard and see a vine that has pushed on one side and spur positions on the other side that haven't pushed yet, that's probably Botryosphaeria, especially if you look at the cordon and see V-shaped cankers.”
To investigate the scope of the problem, researchers conducted a survey to look at close to 2,000 grapevine cankers in California in 21 counties and 200 vineyards. What they found was that a large percentage of what used to be considered Eutypa were actually Botryosphaeria.
“This is a very important pathogen in grapevines,” Gubler says. “The disease has received a lot of attention around the world in the last 10 years. I don't think it's new to California. It's just been ignored. We didn't think that Botryosphaeria could move through the wood fast enough during the spring push to kill the spur position. We now know that we do have at least four species of Botryosphaeria that can move more than 25 centimeters through the wood and kill these spur positions.”
There are several species of Botryosphaeria that used to be lumped into Eutypa species because the symptoms were so similar. “This is something we've cleared up and now have the ability to identify,” Gubler says.
Spore release is tightly associated with rainfall and sprinkler irrigation. In trials, researchers found that in the absence of rainfall, once they turned on sprinklers, they started trapping spores.
“The source of the inoculum is probably primarily vineyards,” Gubler says. “We've also seen some of these fruiting bodies on native vegetation and trees such as almonds and cherries.”
Twelve species have been isolated around the world. Nine in California are associated with grapevines and eight of those nine are newly identified species of Botryosphaeria. Several are very severe pathogens and can colonize wood just as rapidly as Eutypa.
“If you get one of these fungi, you're going to want to get rid of it really fast and sanitation is the only way to do it,” Gubler says. “You've got to cut the wood out, burn it or do something to get it out of the vineyard. As far as control is concerned we know that neither of these fungi — Botryosphaeria or Eutypa — can be eradicated from the vine.”
Double pruning is the recommended for Botryosphaeria. Even if positions become infected during the winter it won't move down into the spur positions.
“We just ran our first tests on Botryosphaeria,” Gubler says. “Even the most virulent species can't penetrate that far down during winter months. During the summer it can do it, but not during the winter. During the winter months it will only move about 8 centimeters, so I think we can recommend either double pruning or late pruning for all Botryosphaeria and Eutypa species.”
Some work is being conducted in Australia and California on possible chemical controls that could be utilized to help control the disease in the future.