Effect of Growth-Retardant Sprays on Fruitfulness and Cluster Development of `Thompson Seedless' Grapes

Abstract

SADH at 4,000 ppm and chlormequat at 1,000 ppm were applied to 9Thompson Seedless9 grapevines about 3 weeks before bloom and/or just prior to or at bloom in 1970 and 1971. Shoots of other vines were topped at early-bloom stage. The double spray of chlormequat applied in 1970 increased fruitfulness, as indicated by the number of clusters in the spring of 1971. Berry weight was decreased by both treatments with SADH in 1970, and by both treatments with SADH and chlormequat in 1971. SADH sprayed twice, and both treatments with chlormequat, increased the number of berries per cluster in 1971. Treatments with chlormequat in 1971 decreased rachis length. SADH sprayed twice, and both treatments with chlormequat, increased the number of berries per cm in 1971. Both chlormequat treatments reduced soluble solids in 1971, but the retardants had no effect on total acid or the ratio of soluble solids to total acid. Topping of shoots had no effect on any of the parameters studied.