The Effects of Pruning Level and Post-Budbreak CaneAdjustment on Thompson Seedless Raisin Production and Quality

¹ Department of Viticulture and Enology, University of California, Davis and U.C. Kearney Agricultural Center, 9240 S. Riverbend Avenue., Parlier, CA 93648
² University of California Cooperative Extension, Madera County, 328 Madera Avenue, Madera, CA 93637
³ University of California Cooperative Extension, Fresno County, 1720 S. Maple Avenue, Fresno, CA 93702
⁴ University of California Cooperative Extension, San Luis Obispo County, 2156 Sierra Way, Ste. C, San Luis Obispo, CA 93401.

A three-year study was conducted in each of two Thompson Seedless vineyards 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 quality. The trial vineyards, of differing canopy size, utilized node level treatments of 60, 90, 120, and 120-adjust and 60, 75, 90, and 90-adjust per vine. The node-adjust treatments were intended to reduce inflorescence numbers to near historic district averages. This was accomplished by counting inflorescences after bud break and then severing the appropriate number of canes (1 to 3 canes of 15 nodes each per vine, depending on vine fruitfulness) for crop level adjustment. Increased node numbers resulted in increased shoots and inflorescences but at disproportionate levels due to reduced percent bud break. Other vine adjustments 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 year treatment effects on raisin yield and only occasionally improved raisin grades when comparing the low- and mid-level pruning treatments to the high level. However, regression analysis of overall means showed 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 raisin grade. Cane severance to adjust inflorescence numbers after bud break was only effective in one of three years at each location in improving raisin quality. Yearly inflorescence numbers did not provide an accurate prediction of the response to or necessity of such a treatment. Thus, higher pruning levels would appear to be of greatest economic benefit to growers, and cane severance after bud break is not a predictable benefit for improved raisin quality.

Key words: grapes, raisins, Thompson Seedless, pruning

Submitted on April 15, 1992