Issue link: http://read.dmtmag.com/i/267019
w w w. v w m m e d i a . c o m M a r - A p r 2 014 | V I N E YA R D & W I N E RY M A N A G E M E N T 6 1 cankers on cross sections, but no foliar symptoms. Bot canker is a major cause of vine arm and cordon death in California, and is prevalent in southern San Joaquin Valley. Growers commonly wait until they see disease symptoms before initiating management, which is often too late to prevent further spread and vine loss. At this stage, management may require vine surgery: removal of dead spurs or cordons, and sometimes retraining suckers or live vine parts to main- tain grape production. Dr. Kendra Baumgartner of the USDA Agricultural Research Service at UC Davis is the lead researcher on a major project, "New Detec- tion, Research, and Extension Tools for Managing Wood Canker Diseases," funded by a grant from the USDA Specialty Crop Research Initiative. "In the field we find mix- tures of these trunk diseases and pathogens; it's rare we find just one type," she said. Canker pathogens require rain to trigger ascospore release from fruit- ing bodies (perithecia) that grow on diseased wood. Research indi- cates that Eutypa spore production can occur in areas with annual rain- fall of 13.5 inches or more. Spore release can occur with a minimum rainfall event of 0.08 inches. In Northern California, Eutypa spores are primarily produced in infected vineyards, in apricot and cherry orchards, and less commonly in pear, apple and almond orchards. Eutypa spores can be carried by wind over long distances from Trapping sites represent a range of vine ages, including mature vineyards planted from 1996-2000 and younger vineyards planted from 2008-2011. "We assume any vineyard 8 years old or more will have some type of trunk disease," Baumgartner said. Two types of spore collection tools were placed at each site. One, a low-tech but proven meth- od, uses glass microscope slides attached to vines in the cordon area to catch fungal spores dispersed by rainwater splash. The second is a solar-powered spore trap with a spinning rod to catch airborne spores. The latter traps have proved effective for monitoring powdery mildew spores in vineyards during the growing season (see May/June 2013 issue of V&WM, page 64), but their use for canker spores is being tested with this study. Researchers collected sample slides and spore rods at each site (one to three times a month after a rain) from December through February, and developed high-throughput poly- merase chain reaction lab analyses to identify fungal species present and track population trends. diseased vineyards and orchards, or from native host plants. Spores from species that cause Esca, Bot canker, or Phomopsis dieback are splash-dispersed by rain drops and travel only a few feet when released, but wind-driven rain can carry these spores farther. SPORE TRAPPING STUDY Researchers began a spore- trapping study in December 2013 at six cabernet sauvignon vine- yards in Napa Valley and six in Lodi. + Grapevine canker (or trunk) diseases occur when fungal spores infect pruning wounds. + The diseases of most concern in California are Eutypa dieback, Esca, Bot- ryosphaeria dieback and Phomopsis dieback. + Grapevine canker diseases can be prevented and managed with late prun- ing, double pruning and applying protectants to pruning wounds. + Researchers are testing fungal spore traps, and developing genetic-based analytical tools for early detection in vineyards. AT A GLANCE Researcher and plant pathologist Kendra Baumgartner holds a glass microscope slide used to collect fungal spores in a cabernet sauvignon vineyard in Lodi, Calif. Photo: Ted Rieger