University of California

Effects of 2,4-D and related substances on fruit-drop, yield, size, and quality of Washington Navel oranges


W. S. Stewart
L. J. Klotz
H. Z. Hield

Authors Affiliations

W. S. Stewart was Formerly Associate Plant Physiologist in the Experiment Station, now with the Pineapple Research Institute, Honolulu, T.H; L. J. Klotz was Professor of Plant Pathology in the Experiment Station; H. Z. Hield was Senior Laboratory Technician in the Experiment Station.

Publication Information

Hilgardia 21(7):161-193. DOI:10.3733/hilg.v21n07p161. November 1951.

PDF of full article, Cite this article


From 1946 to 1950, field experiments were conducted to study the effects of 2,4-D and other plant growth regulators on navel oranges, with respect to fruit-drop (both young and mature fruits), yield, fruit size and quality, and susceptibility to water spot.

In 1947, a progress report was prepared for growers. This included some of the results obtained by use of dilute 2,4-D sprays to reduce drop of mature, or nearly mature fruits.

The present paper summarizes the 1947 findings and reports results obtained since that time. The earlier experiments were mainly concerned with effects of 2,4-D applied to trees bearing mature fruits, and the later experiments to those bearing young fruits. Generally, the 2,4-D was added to a mixture containing other spray chemicals. In nearly all cases, satisfactory control of fruit-drop was reported, and there were no reports of reduced yield, lower fruit quality, or tree injury when instructions were followed. When a severe drop of mature navel oranges is anticipated or in progress, spraying with 2,4-D is now becoming standard practice.

Literature Cited

Baker J. L., Nedvidek R. D. Commercial storage of 2,4-D treated and nontreated navel oranges 1947. Unpublished. Report on file at California Fruit Growers Exchange, Research Department, File No. 37. Citrus Fruit Storage, April-June

Batjer L. P., Thompson A. H. Further studies with 2,4-dichlorophenoxyacetic acid sprays in retarding fruit drop of Winesap apple. Amer. Soc. Hort. Sci. Proc. 1947. 49:45-48.

Batjer L. P., Thompson A. H. The transmission of effect of naphthaleneacetic acid on apple drop as determined by localized applications. Amer. Soc. Hort. Sci. Proc. 1948. 51:77-80.

Batjer L. P., Thompson A. H., Gerhardt Fisk. A comparison of naphthaleneacetic acid and 2,4-dichlorophenoxyacetic acid sprays for controlling pre-harvest drop of Bartlett pears. Amer. Soc. Hort. Sci. Proc. 1948. 51:71-74.

Coit J. Eliot, Hodgson Robert W. The June drop of Washington Navel oranges. California Agr. Exp. Sta. Bul. 1917. 290: http://archive.org/details/junedropofwashin290coit

Coit J. Eliot, Hodgson Robert W. An investigation of the abnormal shedding of young fruits of the Washington Navel oranges. Univ. California Pubs. Agr. Sci. 1919. 3:283-368. DOI: 10.5962/bhl.title.29447 [CrossRef]

Ebeling Walter, Klotz L. J. The relation of pest control treatment to water rot of navel oranges. California Dept. Agr. Bul. 1936. 25:360-68.

Ebeling Walter, Klotz L. J., Parker E. R. Experiments on navel water spot. California Citrogr. 1938. 23:410 434

Hodgson Robert W. Some abnormal relations in citrus trees of the arid southwest and their possible significance. Univ. California Pubs. Agr. Sci. 1917. 3:37-54. DOI: 10.5962/bhl.title.31164 [CrossRef]

Klotz L. J., Stewart W. S. Observations on the effect of 2,4-D on fruit-stem die-back in citrus. California Citrogr. 1948. 33:425

Klotz L. J., Boyce A. M., Chapman H. D., Carman G. E., Cree Clarence, Jones W. W., Riehl L. A., Sinclair W. B., Parker E. R., Stewart W. S., Turrell F. M. Water spot of navel oranges. California Citrogr. 1949. 34:122-26.

Marsh R. S., Taylor C. F. Observed residual effects on apples of 2,4-D in a central spray system. Amer. Soc. Hort. Sci. Proc. 1947. 49:59-62.

Parker E. R. Some effects of thinning orange fruits. California Agr. Exp. Sta. Bul. 1934. 576: https://archive.org/details/someeffectsofthi576park

Rohrbaugh P. W. Physiological effects of petroleum oil sprays on citrus. Jour. Econ. Ent. 1941. 34:812-15.

Stewart W. S. Instructions for the use of 2,4-D sprays for control of preharvest drop of citrus fruit 1947. Univ. California Citrus Exp. Sta. Plant Physiology News Letter No. 1, June

Stewart W. S. Effects of 2,4-D and 2,4,5-T on citrus fruit storage. Citrus Leaves. 1948. 28:6 7, 24-27

Stewart W. S., Ebeling Walter. Preliminary results with the use of 2,4-dichlorophenoxyacetic acid as a spray oil amendment. Bot. Gaz. 1946. 108:286-94.

Stewart W. S., Hield H. Z. Effects of water sprays of 2,4-dichlorophenoxyacetic acid and 2,4,5-trichlorophenoxyacetic acid on fruit drop, fruit production, and leaf drop of lemon trees. Amer. Soc. Hort. Sci. Proc. 1950. 55:163-71.

Stewart W. S., Klotz L. J. Some effects of 2,4-dichlorophenoxyacetic acid on fruit-drop and morphology of oranges. Bot. Gaz. 1947. 109:150-62. DOI: 10.1086/335464 [CrossRef]

Stewart W. S., Klotz L. J., Hield H. Z. Progress report on 2,4-D water sprays. Citrus Leaves. 1947. 27:12 13, 16

Stewart W. S., Parker E. R. Preliminary studies on the effects of 2,4-D sprays on preharvest drop, yield, and quality of grapefruit. Amer. Soc. Hort. Sci. Proc. 1947. 50:187-94.

Teske A. H., Overholser E. L. Some effects of 2,4-D upon the foliage of apples and peaches. Virginia Fruit. 1947. 35:15-18.

Vyvyan M. C. Fruit fall and its control by synthetic growth substances. Imp. Bur. Hort. and Plantation Crops Tech. Commun. 1946. 18:

Stewart W, Klotz L, Hield H. 1951. Effects of 2,4-D and related substances on fruit-drop, yield, size, and quality of Washington Navel oranges. Hilgardia 21(7):161-193. DOI:10.3733/hilg.v21n07p161
Webmaster Email: sjosterman@ucanr.edu