Shijian Zhuang,* Gaia Nafziger, Matthew Fidelibus, and Kaan Kurtural
*University of California Cooperative Extension, 550 E Shaw Ave, Suite 210-B, Fresno, CA 93710 (gzhuang@ucanr.edu)

San Joaquin Valley (SJV) has 65% Pinot gris acreage and the majority of Pinot gris crush volume (83%) in California. Strong demand for Pinot gris has prompted growers to restrict the nonbearing period to <2 years, if possible. This requires permanent vine structure establishment the first year, with a crop expected in the second year. Precocious cropping raises the risk of overcropping, with possible carryover effects in subsequent years. To identify the optimum crop level and economic threshold for newly planted Pinot gris vines, a trial was initiated in a commercial vineyard in 2016. Four crop levels, replicated five times, were established three weeks before bloom; 0 (defruited), ½ (one cluster per two shoots), one cluster per shoot, and unthinned vines (no clusters removed). Cluster removal increased fruit set, average berry weight, and soluble solids. Increased cluster compaction on thinned vines did not cause excessive bunch rot, but did partially compensate for the potential yield loss associated with cluster removal. Yield in 2016 was reduced by 6, 28, and 100% with the severity of cluster removal. No thinning was performed in 2017, but yield and pruning weight were measured. The Ravaz index (RI) of vines with ½ cluster per shoot was 8.3 in 2016 and vines in that treatment had the highest accumulated yield across 2016 and 2017. Vines with RI > 10 showed significantly delayed ripening in 2016 and reduced yield in 2017. Thus, young vines with an RI > 10 in their first crop year were overcropped and will likely have reduced yields the following year, while vines with an RI of 10 provided maximum yield without affecting fruit quality and the following year’s crop. The study is ongoing to determine the duration that overcropping in the first year may affect the vines.

Funding Support: University of California Agriculture and Natural Resources and The Wine Group