THE EFFECTS OF PRUNING LEVEL AND POST-BUDBREAK CANE ADJUSTMENT ON THOMPSON SEEDLESS RAISIN PRODUCTION AND QUALITY

A three-year study was conducted in each of two Thompson Seedless vine yards to determine pruning level effects on raisin yield and quality. Cane severance after bud break was also evaluated as a possible means to adjust year-to-year crop level differences for improved raisin qual ity. The trial vineyards, of differing canopy size, utilized node leve l treatments of 60, 90, 120, and 120-adjust and 60, 75, 90, and 90-adj ust per vine. The node-adjust treatments were intended to reduce inflo rescence numbers to near historic district averages. This was accompli shed by counting inflorescences after bud break and then severing the appropriate number of canes (1 to 3 canes of 15 nodes each per vine, d epending on vine fruitfulness) for crop level adjustment. Increased no de numbers resulted in increased shoots and inflorescences but at disp roportionate levels due to reduced percent bud break. Other vine adjus tments to increased node numbers were comparatively small and variable among years and included smaller berries and clusters and lower fruit soluble solids. Ultimately, there were no significant ANOVA year to y ear treatment effects on raisin yield and only occasionally improved r aisin grades when comparing the low- and mid-level pruning treatments to the high level. However, regression analysis of overall means showe d a 0.3 kg per vine raisin yield increase for each additional 15 nodes (I cane) retained, accompanied by a decrease of 3% B and better raisi n grade. Cane severance to adjust inflorescence numbers after bud brea k was only effective in one of three years at each location in improvi ng raisin quality. Yearly inflorescence numbers did not provide an acc urate prediction of the response to or necessity of such a treatment. Thus, higher pruning levels would appear to be of greatest economic be nefit to growers, and cane severance after bud break is not a predicta ble benefit for improved raisin quality.