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

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.