A research team from the Viticulture and Enology Research Center (VERC) at California State University, Fresno has joined with an international agricultural equipment manufacturing company to improve mechanized pruning for wine grapes in California’s San Joaquin Valley.

Leading the project is assistant professor Kaan Kurtural, who holds the Bronco Wine Co. Viticulture Chair at VERC and the university’s Department of Viticulture and Enology.

“As hand labor is becoming more expensive and scarce in the Central Valley, growers are turning more towards mechanization to reduce costs and to increase efficiency and sustain-ability of their wine grape operations,” Kurtural said in outlining the research.

Mechanized pruning of wine grapes is not new, having been introduced in California more than 10 years ago, Kurtural noted. But manufacturers have focused mainly on equipment for high quality wine grapes grown on vertically-shoot-positioned or lyre trellis systems in areas such as the Central Coast.

More recently, companies such as Oxbo International have developed and refined systems designed not only for pruning, but also for shoot and cluster thinning. Key objectives of the current partnership is to test mechanical systems for shoot and cluster thinning on the type of trellis system most commonly found in San Joaquin Valley wine grape vineyards – the California “T,” also known as the California Sprawl.

“The majority of the wine grape acreage in the valley is trained to the California Sprawl due to its initial low cost of installation,” Kurtural said. Growers who have tried to adapt existing mechanized pruning equipment to that system have encountered an assortment of problems because of the way the vines grow along that type of canopy, however. Problems include over-shading of clusters, non-uniform shoot and fruit distribution, uneven fruit ripening, delayed flavor development and over-cropping.

“If we are to remain competitive in the domestic and international wine market, the adoption of mechanical canopy management needs to increase from its current level of 15 percent across California,” Kurtural said.

For this project, the research team is evaluating new mechanical pruning, shoot thinning and cluster thinning machine heads that Oxbo has designed for use on the California Sprawl. The project will feature three treatments: conventional hand pruning and thinning, mechanical pre-pruning followed by hand pruning and thinning, and mechanized pruning and thinning.

Last summer was the first season of the four-year project, and results look promising, Kurtural said.

“We saved close to a quarter per vine in costs, and we did not lose anything in yield or quality,” he said. At 21 cents per vine, 600 vines per acre, that amounts to $126 per-acre savings using a completely mechanized system.

The study is being conducted on Fresno State’s university farm on Cabernet Sauvignon grapes on Freedom rootstock. The vines are trained to a bilateral cordon at 54 inches height with a foliage support wire at 66 inches on a two-wire vertical trellis.

Treatment analysis includes measurement of fruit yield, cluster numbers, average berry size, percent total soluble solids, juice pH, titratable acidity, and anthocyanin and phenolic concentrations. Crop load and leaf area to fruit ratio also will be calculated based on yield and pruning weight per vine.

Confirmation of the positive results over several years of study “would have the potential for having a relatively rapid impact on grape and wine industries in the San Joaquin Valley,” Kurtural said.

Assisting in the project for Oxbo is viticulturist Greg Berg, working out of the company’s Kingsburg sales and service office. Oxbo, which has manufacturing plants in Washington and Wisconsin, has provided funding to help fund the research as well as engineering expertise in the development of custom pruning and thinning heads. Also supporting the research is Bronco Wine Co.