by Deborah Jeanne Sergeant
Vineyard diseases can diminish a vineyard’s profits. Carefully monitoring vineyards and addressing these issues can help growers prevent these losses. To address the topic, Cornell AgriTech, Virginia Tech and Penn State Extension recently hosted an Eastern Viticulture and Enology Forum with presenters Dr. Kendra Baumgartner, research plant pathologist, USDA-ARS/University of California and Dr. Mizuho Nita, associate professor and Extension grape pathologist, Virginia Tech.
Baumgartner listed dieback-type trunk diseases including Botryosphaeria, Cytospora, Esca and Phomopsis. Their main outcomes are dead fruiting positions, yield loss and gradual decline in vine capacity, which may first appear in years six to eight, but “these infections may have appeared years beforehand,” she said. “There’s a multi-year delay between when the infections occur and when you notice dieback in the canopy.”
The slow process is not without symptoms that growers can spot. They can observe missing spurs, dead shoots, dead spurs, stunted shoots and wood canker. “If you cut into the cordons or spurs where you see dieback symptoms, you might see a wood canker,” Baumgartner said.
Phomopsis is more likely in the Northeast, where rain is likely to occur during the growing season. It causes black spots to appear on leaves; the black spot is a spore. “This fungus can make its way into the woody tissues where it can make headway,” Baumgartner said.
Esca can cause improper fruit ripening, spots (also called “measles”) on the fruit and a possible, gradual decline in vine capacity. “Symptoms can first appear in years four to six, but infections happen years before,” Baumgartner said. The leaves appear scorched and brown along the edges with yellowing framing the veins. In other cultivars, it can be more subtle and you may not get all these symptoms, like reddening. The symptoms are extremely variable.
Growers may find that their grapes affected by Esca never ripen, even when it’s nearly harvest time. “Typically, it’s clusters that are near leaves that are affected,” Baumgartner said. “They never measure up, no matter how much cluster thinning you do.”
For table grapes, the blemishes make them unmarketable. Esca affects the wood, as cross-sections show black spots and decay. The wood also displays black lines along the sides. “They look like black, inky lines,” Baumgartner said. “They can cause wood rot or decay. You can see one or both of these symptoms.”
Esca can cause rapid vine collapse or apoplexy. “We don’t know why this happens in some years and not others,” Baumgartner said.
“Young vine decline is not very common, but where it occurs, it’s very damaging,” Baumgartner said. “Vines between three and five years old just never thrive. They are maybe one-third the size of what they would be.” The vines show low vigor and few fine roots. Young vine decline appears to be a combination of Esca and black foot.
Some of the fungi cause mixed infections. “You often find one vineyard with more than one trunk disease and often more than one on one vine,” Baumgartner said. “We don’t know a lot of their sporulation cycles or what circumstances are ideal for their germination. We base our management on our knowledge of a few.” Although that limits growers’ ability to manage them, it’s far less damaging than doing nothing.
These diseases spread through spore distribution. Spores remain dormant until bud break. Baumgartner said spore traps reveal more spore detection in mature vineyards than new ones. “We still get detections in young vineyards, so it’s important in managing trunk diseases in young vineyards,” she said. “But every year, mature vineyards are susceptible.”
Trunks become infected through wounds caused by winter injury, pruning, major changes in the training system and mechanical harvester damage. Pruning wound susceptibility is lowest in the dormant season, which may make that a good time to prune. “It’s something growers can control: when, how and what you do to pruning wounds afterwards to protect them,” Baumgartner said.
“Growers who have access to mechanical pruning machines and have vineyards amenable to mechanical pruning prune down the canes to eight to 10 inches in December or January and in the spring, make the second pruning,” Baumgartner said. “It cuts away any part of the canes that may be infected.”
A more extreme measure is trunk renewal – chopping off the entire top and training it from the remaining shoot. “It’s a difficult technique, as it’s labor-intensive,” Baumgartner said. Growers also must spend three to four years retraining vines. Despite its drawbacks, this method can be cost effective if performed before year 15.
Baumgartner advised identifying symptomatic vines in spring, performing the cut during dry weather and treating the wound with a protectant. “As a grower, you won’t know when you’ll have a dry versus a rainy year,” she said. “Pick a preventative practice and use it every year religiously.”
Nita noted pruning and weed eating often cause injuries that invite trunk diseases. “Once the trunk diseases come in, it shortens the life of your vineyard as a whole,” he said. “If you try to replant, it’s a headache more than anything else. It’s cost prohibitive in some cases to replace these vines.” Instead of the expected 35 years, growers get only 25 to 30 years. Working proactively makes more sense.
Burn any clean-up of diseased material, as it can transmit disease to remaining vines. Sanitize equipment after cutting diseased vines too.
Large producers may want to focus their efforts on their most valuable cultivars. He also advised spraying for Phomopsis a week before bud break for the best results.
Crown gall forms upward on the main truck. Caused by a bacterium, crown gall may also appear on the sides of trunks. “They produce food inside as well,” Nita said. “I’ve seen cases where the grape vines are 20 to 25 years old and they’re surviving and producing. But young vines decline rather rapidly because they go into vascular tissue quickly.”
He advised selecting areas not prone to frost and excess moisture. Heavy soils are also not advisable. “These are place where we’ll get winter injuries, not only for crown gall but trunk diseases as well,” he said.
Some soil borne nematodes can increase the chances of crown gall. Hilling up young vines may protect the graft union. “I try to avoid over-cropping and maintain proper growth of the vine,” Nita said.
When removing unwanted shoots, many growers rub them off with their fingers in the spring; however, once the shoots get thick, this can cause an injury. “Then the crown gall bacteria come in and cause issues,” Nita said. Pruning them off is better.
“Spend the time to tag vines with crown gall or other issues,” Nita said. “It will help monitoring issues.” If crown gall is only in a small area, the producer may be able to retrain the vine; however, if removal of the vine is necessary, as much of the root area as possible should be taken out and the material should be burned.
“Oftentimes, for crown gall or viruses, I recommend applying glyphosate onto the vine, not in the season but in the fall,” Nita said. “Make sure the vine you’re removing is really dead.”