Clusters and foliage of Black Corinth grapes were sprayed with 4-chlorophenoxyacetic acid at concentrations of 10, 25, 50, 100, or 300 p.p.m. Large berries and compact clusters developed when the acid was applied in the range from 10 to 50 p.p.m. Dipping of clusters gave similar results. 2. Parts of Black Corinth vines were sprayed with 4-chlorophenoxyacetic acid at 25 p.p.m. on May 24, May 28, June 3, June 7, or on June 14. June 3 was apparently the earliest time to spray in 1951 to obtain compact clusters with almost no hard seeds. Dipping of clusters gave approximately the same results. 3. Dip applications of 4-chlorophenoxyacetic acid at 50 p.p.m. to Black Corinth clusters resulted in berries as large as those produced after both girdling and application of growth-regulator. 4. Only the parts of clusters of Black Corinth grapes treated with growth-regulator usually developed large berries and thickened pedicels. The compound, or stimulus induced by it, apparently failed to move from the treated area to any appreciable degree.
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Robert J. Weaver (1952) studied this question.