The influence of exogenously applied 2,4- dichlorophenoxyacetic acid on fruit drop and quality of navel oranges (Citrus sinensis L.)

Orchard experiments were carried out in Botswana with the objective of evaluating the effect of 2,4- \ndichlorophenoxyacetic acid (2,4-D) on reducing premature fruit drop. Different concentration levels of \nthe 2,4-D (8, 16 and 20 mg/L were applied exogenously to mature fruit trees of sweet orange (Citrus \nsinensis L.) in the 2004/2005 season. In the 2005/2006 season the 2,4-D treatments ranged from 20 to 40 \nmg/L concentration. There appeared a general increase in fruit drop for the month of October in all \ntreatments but a decrease in fruit drop was observed in the fruit trees with 16 and 20 mg/L 2,4-D \nconcentration, that is, from November through February; with the latter showing the least number of \nfruits that dropped throughout the execution of the experiments. The application of 20 mg/L 2,4-D \nsignificantly reduced fruit drop by more than 50% but higher concentration levels of the plant growth \nregulator significantly increased fruit drop. It was also evident that, small sized fruits were more \nsusceptible to fruit drop than larger fruits. These findings suggested that, 2,4-D can be an effective tool \nto control fruit drop by enhancing retention, as well as improving the quality of navel oranges under dry \nclimatic conditions