Interactive Effects of Mechanical Canopy Management and Reduced Deficit Irrigation on Shiraz Grapevines

Canopy microclimate of Shiraz/1103P grapevines were altered and exposed to Reduced Deficit Irrigation (RDI) with varying severity and timing. Four canopy levels were imposed by dormant pruning the vines to 42 spurs (control), mechanically pruning others to 4? hedges and mechanically thinning shoot and cluster density to 5 shoots/foot of row , 9 clusters/foot (CLL); 7 shoots/foot, 15 clusters/foot (CLM); and 16 shoots/foot , 17 clusters/foot (CLH), respectively. Control vines were irrigated to 70% of Et until harvest (RDIC). Other vines either received 70% of full vine Et until to veraison, after which the rate was cut to 50%of Et (RDIL) or had their irrigation cut to 50%of Et before veraison (RDIE), but not thereafter. At veraison, the shoots exposed per hectare were 53%and 39%lower for the CLL, and CLM; but 43%higher for the CLH when compared to Control. The distance between shoots was 137%and 81%higher for the CLL and CLM, but 29%lower for the CLH compared to Control. Compared to control, the leaf layer number was 55% and 50% lower for the CLL and CLM, but 20%higher for the CLH. The RDIE and RDIL treatments lowered the leaf layer number by 22%and 10%, respectively compared to RDIC. Berry weight was 2%, 5%, and 11% lowered by the CLL, CLM, and CLH, respectively. RDIE also reduced berry weight by 16%at harvest compared to RDIC and RDIL. Yield was reduced by 33%, 29%by the CLL and RDIE, but increased by 5% and 17% for the CLM and CLH, respectively. The CLL and CLM reduced the leaf area to fruit ratio by 33%, and 54%respectively whereas the RDI treatments did not affect the leaf area to fruit ratio. There was an interaction of canopy management and RDI stress on wine total phenols, tannins, and anthocyanins whereas the CLM with RDIL had the highest tannins and total phenolics. The highest wine anthocyanins were seen with the CLM with the RDIE. This study provides important information for growers considering mechanizing canopy management operations while scheduling reduced deficit irrigation, where best results were achieved with a combination of CLM and RDIE treatments. That translates into 7 shoots per foot of row after mechanical shoot thinning, 15 clusters per foot of row after cluster thinning concurrent with shoot thinning resulting in 3 to 4 leaf layers with shoots 2 inches apart along the cordon, yielding 9.2 to 10 tons/acre with berry size reduced by 5% on shorter rachises, and 420 mg/L malvidin-3-glycoside eq, 1045 mg/L CE of total phenols, 165 mg/L CE of tannins and 873 mg/L CE of non-tannin phenols in wine.