. Auxins and plant growth. Auxin; Plant growth promoting substances. Pre-Harvest Fruit Drop 245 2,4,5-T, the effect lasts for from 4 to 6 weeks. This compound has es- sentially displaced all others in the control of pre-harvest drop of apples in the United States. The amide of 2,4,5-T has been reported as being particularly effective in the control of fruit drop (Edgerton and Hoffman, 1953). Not only do the phenoxy acid auxins show a longer lasting effect in the control of fruit drop, but they take a considerably longer time to begin their effects after spraying. Naphthaleneacetic acid holds f
. Auxins and plant growth. Auxin; Plant growth promoting substances. Pre-Harvest Fruit Drop 245 2,4,5-T, the effect lasts for from 4 to 6 weeks. This compound has es- sentially displaced all others in the control of pre-harvest drop of apples in the United States. The amide of 2,4,5-T has been reported as being particularly effective in the control of fruit drop (Edgerton and Hoffman, 1953). Not only do the phenoxy acid auxins show a longer lasting effect in the control of fruit drop, but they take a considerably longer time to begin their effects after spraying. Naphthaleneacetic acid holds fruits on after only 2 or 3 days from the spraying time, but 2,4,5-T and 2,4,5-TP do not generally control drop effectively for some 10 to 17 days after spraying. Such delays in effectiveness can be seen in the data of Erickson et al (1952). A few reports indicate a retarded fruit drop as early as 4 days after application of 2,4,5-TP (Southwick et al, 1953), but such early control is not general. A good many other auxins ha\e been tested for this use with less success. It may be of interest to note that /i?-propionic and yg-butyric phenoxy acids are ineffective in prevention of fruit drop (Osborne and Wain, 1951). a. o Q UJ o a: Ld 15 DAYS TIME AFTER AUXIN APPLICATION Fig. 104. The relative effectiveness of naphthaleneacetic acid (NAA) and a-(2,4,5-trichloiophenoxy)-propionic acid (2,4,5-TP) in controlling drop of Mcintosh apples (Southwick et al, 1953), showing the more rapid control by NAA and longer duration of control by 2,4,5-TP. Both auxins used at 20 Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Leopold, A. Carl (Aldo Carl), 1919-. Berkeley, University of California Press
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