Something has been reddening leaves, and eventually killing vines, in young Syrah vineyards along California’s Central Coast while researchers and growers probe to learn the cause and how to deal with it.
Known as “Syrah disorder” in California, the problem has some symptoms that resemble those of the equally mysterious “Syrah decline” of that variety in France and Australia, according to Mark Battany, farm advisor for San Luis Obispo and Santa Barbara counties.
Recently Battany spoke to growers in Salinas at a Central Coast Winegrape Seminar, where he said a statewide survey during 2002-2003 revealed the disorder appears to be concentrated in vineyards on the warmer areas of the coast.
He said among suspected links with the dieback of Syrah vines are leafroll virus, salinity, and perhaps herbicide sensitivity.
Vines three to five years old are commonly affected, but not all vines in a block pick up the disorder. Some growers, Battany said, after replacing vines here and there, have reached the point where it may be more economical to remove the entire block and replant.
At any rate, he said he suspects it is a complex of problems, and University of California and USDA researchers are applying “heavy duty science” to find a solution.
Although leafroll virus, or something similar, is a prime suspect and erodes fruit quality elsewhere in the region, affected vines did not show quality problems at the same time, even though they did die.
Battany said leafroll-like symptoms appear in affected blocks, although repeated tests for leafroll virus have been negative. “But this doesn’t mean it’s not there, only that it couldn’t be identified.”
He surveyed 81 blocks having symptoms and more than half of them tested positive for more than one virus.
“Salinity is definitely an issue in some areas, especially where it exacerbates drought stress, and this year, because of the dry weather, I expect to see more problems than in the past.”
Any connection herbicides might have is being investigated in a survey that will continue the next couple of seasons, he added.
Citing typical symptoms in California, Battany said first is a reddening canopy of affected vines in late July, plus in many cases, but not all, fruit has poor color and sugar development.
Considerable variability in leaf symptoms, from reddish blotches to necrotic, “potato chip-like” deformation of leaves occurs from one affected vineyard to the next. Foliar symptoms become more severe with drought, excessive crop load, or other stress on the vines.
Some vineyards show scarring and pitting of vines, along with short internodes in contrast to the variety’s usually long internodes. Additional signs are cracking and fissures and seeming incompatibility along the union of scions and rootstocks.
“The vines typically fail to bud out in the spring and appear weak. Then the following year they just don’t grow at all.”
These symptoms are consistent with most of the calls Battany said he has received from growers.
He also observed that after harvest, affected vines, once they were treated with fertilizer, did start regrowth. “So these vines do have the ability to make nice, green growth, but they just can’t do it under any kind of stress.”
Focusing on moisture stress, in 2002-2003 a Santa Barbara grower placed additional drip emitters on third-leaf vines having the red-leaf coloration.
“They decided to keep the block another year and with the extra emitters for red-leaf vines, irrigating them twice as much as normal,” Battany said.
“The extra water kept the red leaves from showing up, but the problem was the fruit quality was just as bad as it was with the other vines receiving the normal irrigation. So there is definitely something else going on in those vines.”
Suspected salinity problems, Battany said, showed up in one block having “potato-chip leaves” in 2003 and 2005 but not in 2004 or 2006. One possibility could be gypsum management or irrigation water chemistry, although the vineyard has multiple soil issues. Without sufficient winter rainfall to leach salts from the root zone, they accumulate to stress the vines.
Another riddle, both in California and France, is why the disorder strikes Syrah but not other varieties. The answer may lie in the traits of the variety.
“Syrah is considered to be anisohydric, which means that under water stress its stomata open and cause a negative water potential in comparison to other varieties,” Battany said.
“Grenache, on the other hand, is isohydric with more of a stomatal closing response to drought stress.” His trials thus far to investigate the differences further have not been conclusive.
The possibility of herbicide sensitivity is another question. One herbicide-treated Syrah vineyard showed dieback of scions but not rootstocks, and more tests will be needed.
Battany is sending samples of affected vines to plant pathologists at the University of California, Davis, for extensive tests to hopefully identify which viral pathogens may be at work in causing the dieback.
Larry Bettiga, farm advisor for Monterey, Santa Cruz and San Benito counties, reported results of his multi-year research with vertical trellising systems for Merlot grapes.
Briefly describing those systems, he said the Scott Henry system originated in Oregon as a way to manage high vigor vines by arranging canes in upper and lower tiers. The Smart-Henry is a cordon version of the Scott Henry, and the Smart-Dyson, developed in Gilroy, uses bilateral cordons. These were compared alongside bilateral cordons with vertical shoot positioning trellising.
He set out in 1998 to learn if there are differences in fruit maturation between upper and lower tiers, if higher production of the systems affects fruit quality, and if the lower canopies maintain long-term vigor.
“After nine years in this trial, the Smart-Dyson seems to be the one that has the highest potential for minimizing differences in ripening and maybe differences in vigor,” Bettiga said. The Smart-Dyson has been the most popular of the three among Central Coastal growers.
Although slight differences were seen between maturity of upper and lower tier fruit in the early years, he said the effects dissipated with time.
Noting the vertical systems work well for low to moderate vigor vines, Bettiga said the concept is also suited to mechanical harvesting and other practices in Monterey County.