University of California

Response of Thompson Seedless grapes to 4-chlorophenoxyacetic acid and benzothiazol-2-oxyacetic acid


Robert J. Weaver
Stanley B. McCune

Authors Affiliations

Robert J. Weaver was Lecturer and Associate Viticulturist in the Experiment Station, Davis; Stanley B. McCune was Senior Laboratory Technician in the Department of Viticulture, Davis.

Publication Information

Hilgardia 27(6):189-200. DOI:10.3733/hilg.v27n06p189. October 1957.

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This paper presents the results of two studies of plant regulators, one on 4-chlorophenoxyacetic acid (4-CPA) (also known as para-chlorophenoxyacetic acid or PCPA), the other on benzothiazol-2-oxyacetic acid (BOA).

The plant regulator 4-chlorophenoxyacetic acid (4-CPA) has been used commercially to increase berry size in Thompson Seedless grapes (2, 5, 6).4 There have been for some time, however, several problems relating to its use that have required further study. One question concerned the importance of the foliage as an avenue for entry of the compound into the fruit. Another was whether the use of 4-CPA resulted in a delay in ripening. Still another problem concerned the influence of the level of cropping on the response to the compound. These problems formed the basis of our experiments with 4-CPA, which extended over a four-year period.

The second plant regulator studied-benzothiazol-2-oxyacetic acid (BOA)—has been shown to cause a delay in ripening in Thompson Seedless (3, 4). In 1955 and 1956 the following studies were made in California in order to obtain further and more detailed information: The effect of various concentrations of benzothiazol-z-oxyacetie acid on Thompson Seedless; the relation of stage of development of the vine to application of the regulator; and the effect of the compound on rate of ripening of fruit.

Materials and Methods

Mature vines of Thompson Seedless in irrigated vineyards were pruned to four or five canes bearing from eight to 12 buds for the experiment.

In the University of California vineyards at Davis, the ammonium salt of 4-chlorophenoxyacetic acid was used, and the diethanolamine salt of the acid was utilized in the trials in commercial vineyards. The sodium salt of benzothiazol-2-oxyacetic

Literature Cited

[1] Jacob H. E. Girdling grape vines. California Agr. Ext. Service Cir. 1931. 56:

[2] Weaver R. J. Further studies on effects of 4-chlorophenoxyacetic acid on development of Thompson Seedless and Black Corinth grapes. Amer. Soc. Hort. Sci. Proc. 1953. 61:135-43.

[3] Weaver R. J. Effect of benzothiazol-2-oxyacetic acid in delaying maturity of grapes. Science. 1954. 119:287-88. DOI: 10.1126/science.119.3087.287 [CrossRef]

[4] Weaver R. J. Use of benzothiazol-2-oxyacetic acid to delay maturity of grapes. Bot. Gaz. 1955. 116:266-73. DOI: 10.1086/335870 [CrossRef]

[5] Weaver R. J., Williams W. O. Response of flowers of Black Corinth and fruit of Thompson Seedless grapes to applications of plant growth-regulators. Bot. Gaz. 1950. 11:477-85. DOI: 10.1086/335618 [CrossRef]

[6] Weaver R. J., Winkler A. J. Increasing the size of Thompson Seedless grapes by means of 4-chlorophenoxyacetic acid, berry thinning and girdling. Plant Physiol. 1952. 27:626-30. DOI: 10.1104/pp.27.3.626 [CrossRef]

[7] Winkler A. J. Pruning and thinning experiments with grapes. California Agr. Expt. Sta. Bul. 1931. 519:

Weaver R, McCune S. 1957. Response of Thompson Seedless grapes to 4-chlorophenoxyacetic acid and benzothiazol-2-oxyacetic acid. Hilgardia 27(6):189-200. DOI:10.3733/hilg.v27n06p189
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