Syrah grape vines trained to bilateral cordons have similar productivity with in-row spacings of 4, 8, or 12 feet, although yields on quadrilateral cordons peak at a spacing of 4 feet. At equal spacings, quadrilateral cordon vines of the red wine variety produce about 50 percent more fruit per acre than bilateral cordon vines.

Those are conclusions drawn by Nick Dokoozlian, University of California Cooperative Extension viticulture specialist at the Kearney Research and Education Center at Parlier, from his studies begun there in 1999.

At the recent Grape Day at the center, Dokoozlian said little attention has been paid to the influence of in-row spacing on vine productivity and canopy microclimate in the San Joaquin Valley. That's why he began the trials to examine the interaction between spacing and training systems on light microclimate, canopy characteristics, and cluster exposure.

The trials are Syrah on Teleki 5C rootstock planted in 1997, with portions having vines spaced at 4, 6, 8, 10, or 12 feet in the row and trained to either bilateral or quadrilateral cordons. Distance between the east-west-running rows is 11 feet.

Cordon height for both systems is 54 inches, and on the bilateral cordon vines a single catch wire was placed 12 inches above the cordon. Fruiting curtains of quadrilateral cordon vines were separated 22 inches, and a 30-inch cross arm was placed 12 inches above the cordons. All treatments were pruned to about two, two or three-bud spurs per foot of cordon length.

“With this trial,” Dokoozlian said, “we wanted to look at the effect of in-row spacing on vine vigor by selecting Syrah, one of the most vigorous red wine varieties, and 5C, a fairly vigorous rootstock if it has enough water.”

Two schools of thought about in-row spacing are current in the California wine grape industry, he noted. “Some support the concept that vine balance is improved at high-vigor sites by decreasing in-row spacing. This group generally believes that increased plant competition under close in-row spacing, less than 6 feet, leads to vine devigoration or reduced vegetative growth.

“On the other hand,” he continued, “many feel that vine balance can be improved at high-vigor sites by increasing in-row spacing and allowing each vine to carry a larger permanent structure or cordon biomass.”

Dokoozlian also cited earlier UC studies that showed that as in-row spacing decreases from the optimum, trunk size, crop load, and total vegetative growth per vine generally decrease. However, he added, when measurements are expressed per unit of row length, total vegetative growth increases and yield decreases. As more vegetation appears, canopy density and interior shading of the fruit increase, causing a decline in production efficiency and yield.

Establishment periods

He said there was no problem getting bilateral cordon vines, including those 12 feet apart, established by the end of the second growing season in his trials. “With the quadrilateral vines, however, it was a different story. By the end of the second season we had only 30 to 40 percent of the vines on 10- or 12-foot spacings fully trained. By the end of the next season, the first growing season, everything was fully established.”

Among various observations taken in the trials, Dokoozlian found that cordon and trunk diameters for both systems showed that 4-foot and 6-foot spacings reduced initial vine size compared to wider spacings and that cordon diameters were significantly greater for bilateral vines than for quadrilateral vines.

Taking into account the greater number of buds on a quadrilateral vine than a bilateral vine, he said there is little difference in tons per acre between the two. “As long as we fill the wire in with spurs, we don't see much difference in yield. There is one exception: we saw a trend toward higher production if the quadrilateral vines are closer together. It may be that if we put the quadrilateral vines more than six feet apart, we are asking a lot of them.”

Dokoozlian said little difference was seen in quality of wines made from the fruit of the different spacings. Fruit from each treatment was picked at the same sugar level, 24 degrees Brix, and maturity of all the fruit occurred within a week.

Spacing ‘hypothesis’

One “hypothesis” of North Coast growers, he said, is that as in-row spacing is decreased, vines are smaller and smaller and berry size is decreased as a result. (Larger berry size is desired as a source of color for wine.) “Under conditions here in the central part of the San Joaquin Valley, we have not seen such a trend. In general, berry weight was not affected, and the differences in yield components are cluster weights from more berries per cluster.”

Analysis of compounds in berries showed that color components were slightly higher in the quadrilateral vine fruit. “That's because as we increase the in-row spacing, we get more light into the canopy of the vines. This was without any leaf removal or shoot positioning, just letting the shoots fall as they may.” Light values within the canopy were measured by instrumentation.

Speaking on vine spacing in general, Dokoozlian said “it's a matter of how close we can put rows together and still farm efficiently. If you go from 10 feet down to 8 feet between rows, you dramatically increase the number of spurs per acre, but you also have to balance that with whether you can farm the vines that close.

“In the SJV we've settled on an industry standard of 10-foot rows for bilateral cordons — some growers have gone to 9 feet — but if you go any closer you'll need some trellis alteration, which is expensive. For quadrilateral cordons, you need at least a foot more width.”

Fill with spurs

Once the width of the middles is set, the in-row spacing should be determined “to fill the wire with spurs,” he said. “As a guideline here in the SJV, going into the third season after planting we want to have the cordon completely filled with spurs. You don't want a wide spacing that will leave gaps. On the other hand, you don't want the in-row spacing too dense because there's no sense in buying more vines and rootstocks than you need, and under some conditions you can have problems with excessive vigor.”

Syrah, a variety originating in the Rhone Valley of France, turned California growers' heads in the late ‘90s as an alternative to the Cabernet Sauvignon-Chardonnay-Zinfandel-Merlot line-up.

By 2002, nearly 12,000 bearing and more than 4,000 non-bearing acres of it were in the ground. Counties with leading acreages (bearing and non-bearing) are: San Luis Obispo, 1,884; Sonoma, 1,726; San Joaquin, 1,668; Madera, 1,611; Monterey, 1,341; Santa Barbara, 1,330; and Fresno, 1,003. In Australia the variety is known as Shiraz.