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)

Direct sunlight and heat waves in arid, warm viticultural regions can reduce fruit quality by inhibiting anthocyanin biosynthesis, promoting anthocyanin degradation, hastening acid metabolism, and causing direct yield loss due to sunburn. Such damage can cause significant economic loss for wine grape growers in the San Joaquin Valley (SJV) of California. The potential for CaCO3 foliar spray to prevent such damage was investigated in 2017. A random complete block design was employed with three treatments: two rates of CaCO3 plus an untreated control, each replicated five times. Foliar spray of CaCO3 using an air blast sprayer was applied monthly after fruit set, with a total of four sprays during the season. Midday leaf water potential (LWP) and canopy temperature were measured weekly from the onset of bloom. Fruit-zone photosynthetically active radiation (PAR), leaf gas exchange, and berry ripening were tracked weekly from the beginning of veraison. Yield components and berry composition were measured at harvest. At the dormant period, pruning weight was collected to calculate Ravaz index (kg/kg). Foliar spray of CaCO3 lowered canopy temperature with little effect on LWP. Slightly higher berry total soluble solids accumulation was observed when CaCO3 was sprayed. No other differences in yield or berry composition were found among treatments. When correlation analysis was performed to identify the key factors impacting berry anthocyanins and phenolics, fruit-zone PAR and pruning weight were the most significant variables. The results indicate that in the SJV, fruit zone exposure and vine vigor had a greater impact on berry anthocyanins and phenolics than CaCO3 treatment.

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