Effectiveness of thinning agents and the removal of some branches of grape rachis on cluster looseness

Campbell Early' flower clusters were sprayed with 50 ppm ethychlozate, 50 ppm ethephon and 1, 200 ppm carbaryl (NAC) at full bloom to test their effectiveness on berry thinning, berry quality, and the rate of flower abscission. The removal of some branches on the cluster rachis 2024 days after spray treatment was also investigated. 1. To reduce the number of normal berries per cluster and the length of rachis, ethychlozate, together with removal of the basal one or two branches on the rachis, produced looser clusters (less compact) than the spray treatment alone. Removal of cluster tips alone (23 cm) had little or no effect on cluster looseness. 2. Spraying with NAC and ethephon also resulted in loose clusters; the decreasing order of effectiveness was : ethychlozate>NAC>ethephon. When each chemical spray treatment was combined with the removal of the basal three branches of the rachis, the least compact clusters were obtained. 3. Ethychlozate tended to increase berry size, regardless of the removal treatment, but NAC and ethephon did not. Sugar contents of the juice were not influenced by any treatments but the titratable acidity was increased by the NAC spray. The removal of part of the rachis tended to decrease titratable acidity. 4. When vines were sprayed with ethychlozate, a peak of flower abscission appeared after 58 days, whereas, the peak of maximum flower abscission occurred 910 days on the untreated control vines. Flower abscission began immediately after ethephon treatment but the maximum abscission occurred 56 days later. Flower abscission with NAC occurred steadily for 510 days after treatment without reaching a maximum. 5. These results suggest that the removal of some basal branches on the cluster rachis after a spray application of ethychlozate or NAC can be used for improving cluster looseness.