Relative Effectiveness of the Mono-, Di-, and Trichlorophenoxyacetic Acids in Retarding Abscission of Mature Apples

1. The relative effectiveness of a complete series of highly purified mono-, di-, and trichlorophenoxyacetic acids in retarding the abscission of mature fruits of six varieties of apples was studied. The pentachloro- and one tetrachlorophenoxyacetic acids were also included in the experiment. 2. Each of the sixteen phenoxy compounds was applied at 1% concentration in a carrier composed of one part Tween 20 and four parts lanolin about 3 weeks before the usual harvest date for each variety. A narrow band of each acid mixture was placed at the abscission zone of each of ten tagged fruits on one tree of each variety. 3. 3,4,5-Trichlorophenoxyacetic acid was highly effective in retarding abscission of all six varieties, while 4-chloroand 2,5-dichlorophenoxyacetic acid were highly effective on five varieties. Four acids, 3-chloro-, 3,4-dichloro-, 2,3,4-trichloro-, and 2,4,5-trichloro-, were highly effective on four of the six varieties. Abscission of two varieties was effectively retarded by 2,4-D, while only ...