Response of Certain Varieties of Grapes to Plant Growth-Regulators

In one experiment, formulations of fifteen growth-regulators were separately applied to Black Corinth grapes by dipping clusters of the flowers at full bloom. Applications of 4-chlorophenoxyacetic acid, alpha-(1-naphthoxy)-propionic acid, 2,3,5-triiodobenzoic acid, N-2-chlorophenylphthalamic acid, N-1-naphthylphthalamic acid, and N-phenylphthalimide resulted in some compact clusters with some large berries containing seeds. 2. In a second experiment, clusters of Black Corinth were dipped at full bloom or 4 days later into formulations of beta-naphthoxypropionic acid or 4-chlorophenoxyacetic acid. Compact clusters failed to develop after applications of the former compound, but treatment with 4-chlorophenoxyacetic acid at 10, 50, or 100 p.p.m. resulted in large, compact clusters after each treatment. With the higher concentrations of the acid used, correspondingly heavier clusters developed. A higher percentage of berries of the first treatment contained seeds than did those of the later one; clusters of the later treatment were heavier. 3. When Black Corinth vines at full bloom were sprayed with 4-chlorophenoxyacetic acid at 25 p.p.m., many large clusters developed. Average weight of fruit per vine for ungirdled but sprayed, girdled but unsprayed, and ungirdled and unsprayed was 17.3, 22.4, and 1.8 pounds, respectively. 4. Flowering clusters of White Corinth and Black Monukka grapes dipped in 4-chlorophenoxyacetic acid at 5 or 50 p.p.m. developed large compact clusters of fruit. A similar treatment with Sultana, Thompson Seedless, Muscat of Alexandria, and Hunisia induced the setting of many "shot" berries. Similar applications of other growth-regulators usually resulted in varying degrees of injury. Applications of growth-regulators to varieties containing seeds resulted in no apparent enlargement of berries. 5. Thompson Seedless vines sprayed with 4-chlorophenoxyacetic acid at 5 or 20 p.p.m. after the shatter of berries developed larger berries than did ungirdled, unsprayed vines.