The growing popularity of two relatively new California wine varieties has brought a boost to the wine grape growing industry in the San Joaquin Valley.

The cultivars Pinot Grigio and Shiraz have seen strong sales in recent years; and since more than 70 percent of grapes for those wines are grown in the valley, growers and bottlers have seen positive returns on their investments years ago in these varieties.

A potentially serious production problem has arisen, however, and has prompted leading producers to request assistance from Fresno State viticulture research specialist Kaan Kurtural.

“What’s happening is that these large vineyards are not producing like they used to,” Kurtural said. “It’s due to the lack of available labor to keep up canopy management in large acreage commercial vineyards, after dormant pruning is done.”

Mechanical pruning is faster and more economical than hand pruning, but the settings used for controlling bud development in Pinot and Shiraz have proven suspect.

Through the American Vineyard Foundation, industry leaders requested Kurtural to develop and test some new methods that could bring production back up. So in consultation with a viticultural specialist from Bronco Winery and a mechanical pruning technician from Oxbo International, Kurtural developed several treatments to be incorporated and tested over the 2009-10 growing season in commercial fields managed by Bronco in the southern San Joaquin Valley.

“We brought up yields quite a bit – from four to five tons per acre to 11, and to 13 in one case,” he said. “And the great thing is, we also saw better fruit color and smaller berry size. It looks like we have better fruit quality overall.”

Another positive result of the work was the number of Fresno State viticulture and enology students who were able to gain valuable research experience through the project. Over the last year, 10 students, at both graduate and undergraduate levels, helped to set up field treatments, conduct sampling, and do analysis work in the laboratory. In August they were involved in harvesting the grapes, overseeing transport to a winery and crushing. Now several of them are involved in the wine-making process.

An equally important part of the research is to test the wines made from the various treatments. Once all the wines are finished, samples will be collected from all the test lots and saved for chemical and sensory evaluation. That part of the process also will be directed by students.

Researchers are seeking support for two more years to further refine pruning techniques and to verify the positive results obtained in the first year, Kurtural said.

For more information on this project, Kurtural may be contacted at