Immediate and Residual Effects of Succinic Acid, 2,2-Dimethyl Hydrazide (Alar) on Young ‘Delicious’ Apple Trees1

Abstract

Succinic acid, 2, 2-dimethyl hydrazide (Alar) sprays were applied at 3,000 and 10,000 ppm to vigorous young ‘Delicious’ apple trees in which yields were limited by insufficient bloom. Sprays applied at the high concentration after harvest in 1965 not only delayed bloom the following spring but also caused mortality of fruit buds and individual flowers. Alar sprays applied shortly after full bloom in 1966 retarded shoot elongation more effectively than the postharvest sprays applied the previous fall, but both were about equally effective in retarding fruit growth and promoting fruit bud formation during the 1966 growing season. The postharvest sprays caused an oblate fruit shape the following year. Alar sprays increased fruit firmness, but did not significantly affect soluble solids or titratable acids. The Alar-induced flowering was responsible for large increases in yield in 1967. Trees which were induced to flower profusely had a very light return bloom in 1968.