Issue link: https://read.dmtmag.com/i/635697
16 FEBRUARY 15, 2016 Good Fruit Grower www.goodfruit.com In addition, pruning wounds should be treated with a protectant before rain. Dr. Kendra Baumgartner, a grapevine pathologist with the USDA Agricultural Research Services at the UC Davis cam- pus, has been studying trunk diseases in grapevines. In a 2013 survey, Baumgartner found that California growers were hesi- tant to use these preventative practices in newly established vineyards, presumably out of concern about potential economic losses. She followed that survey with an economic analysis in 2014, showing that early adoption of preventive practices can significantly reduce the impacts of trunk diseases, generating financial returns close to those of a healthy vineyard. Baumgartner and postdoc Renaud Travadon joined Jonathan Kaplan of California State University, Sacramento, in a similar study of Washington's wine industry. The 2015 analysis simulated production of Cabernet Sauvignon, Chardonnay, Merlot and Riesling — the four leading wine grapes accounting for 75 percent of Washington's wine grape production. The researchers constructed a repre- sentative bioeconomic model for wine grape production in an infected vineyard. The model simulated production from a healthy vineyard for a 20-year lifespan and subjected it to a trunk disease. In one case, it assumed no preventative action had been taken, and in the other, it simulated double pruning with varying degrees of success. Generally, the results showed that the earlier double pruning is started in the vineyard and the greater the efficacy of pruning the disease from the vines, the more likely the positive overall net returns for the vineyard at the end of 20 years. The efficacy depends on the timing of the second pruning pass, in relation to pruning-wound susceptibility. Pruning wounds made in early winter (in California, December and January, some- times even in February) are more suscep- tible to infection than wounds made later in the dormant season (March). That's because winter rains induce spore release and there tends to be more rain (and more spores) in early winter. Also, cold temperatures are thought to lengthen the wound-healing process, and early winter tends to be colder. Given the variation in disease-control efficacies in the scientific literature, there is great uncertainty about the timing of preventative practices, Baumgartner told Good Fruit Grower. Until detailed knowledge is available on the impacts of environmental conditions on infection — specifically, those conditions that favor spore release, transport, deposition and germination on pruning wounds — and the healing process of grapevine wounds, researchers are left to make uniform assumptions about efficacy. "Nonetheless, the more wounds protected each year, even if it is only 50 percent, the better," she said. "Because the infections by trunk pathogens are chronic, each infected pruning wound eventually results in a dead spur and thus fewer fruit clusters on the vine. Along this line of reasoning, it makes sense to start preventing trunk diseases in young vineyards." The Riesling vineyard saw a positive overall net return at the end of 20 years when double pruning was implemented in years three and five. If adopted in year 10, the results were negative overall net returns. The researchers found similar results for Cabernet Sauvignon; however, the Cabernet Sauvignon vineyard also saw positive returns when double prun- ing was adopted in year 10, but only at higher efficacy rates. Merlot showed pos- itive returns only when double pruning was implemented in years three and five and only at high efficacy rates. However, double pruning is no guar- antee for less-profitable cultivars: It never produced positive returns in the Chardonnay model, regardless of how early in the vineyard's life it was imple- mented or at any level of effectiveness. Overall, double pruning resulted in greater overall economic returns over a 20-year vineyard lifespan compared to doing nothing to combat trunk diseases, the researchers found. The study focused only on using prac- tices that prevent trunk diseases and did not examine methods for dealing with an already-infected vineyard, Baumgartner said. Growers who don't yet have a trunk disease confirmed should consider dou- ble pruning. She said those who already have a confirmed disease problem might consider something that growers in California are employing with success: retraining or vine surgery, a form of trunk renewal. It involves sawing off the dead cordon, or a cordon that has many dead spurs, and retraining a new one from new canes. For vines with more than one infected cordon (or if you only have one cordon per vine), you can retrain a new vine with a trunk sucker and saw off the old vine at the base of the trunk. Because fungi enter the vine mostly from the pruning wounds, the infection tends to localize in the canopy, which makes this option viable as long as grow- ers don't wait too long, Baumgartner said. "It's something that can be cost effec- tive as long as the vineyard hasn't suffered so many years of yield losses," she said. "As long as you haven't dug yourselves down into a deep hole already; by then, you're better off cutting your losses and starting from scratch." • PHOTO COURTESY OF KENDRA BAUMGARTNER The foliar symptoms of Eutypa dieback appear in spring. Shoots growing from infected spurs will be stunted, with shortened internodes. The leaves are yellow and deformed, with veins that tend to grow in a parallel orientation, and have tattered, slightly scorched margins.