Abstract
Mature Vitis vinifera `Tokay' grapevines were sprayed with 2,4-dichlorophenoxyacetic acid (2,4-D) or 4-(2,4-dichlorophenoxy) butyric acid (2,4-DB) at concentrations from 0.01 to 10 ppm in the spring, or from 10 to 50 ppm in the summer. The spring-sprayed shoots were analyzed for residues 0, 3, 7, and 14 days after treatment. Whole shoots 14 days after application had residues of 2,4-D or 2,4-DB with all treatments of 1 ppm or more. Sprays of less than 0.1 ppm produced no leaf symptoms or detectable residues. By 1 day after the spring treatment, the 3- and 10-ppm spray applications of both 2,4-D and 2,4-DB had resulted in epinastic response. By 2 weeks, 2,4-D at 10 ppm had caused the death of shoot tips, whereas 2,4-D at 3 ppm and 2,4-DB at 3 and 10 ppm stopped growth but did not produce typical leaf symptoms. All summer treatments killed the shoot tips, but none caused 2,4-D-type leaf symptoms until the following spring, after the shoots were 2 to 3 feet long. Droplet tests in mid-April with 2,4-D resulted in cleared-vein symptoms in discrete areas of leaves 9 days after treatment, provided the leaves were less than one-fourth full size at treatment. Symptoms were evident on all such leaves treated with 0.0001 to 0.001 µg 2,4-D. There was no indication of translocation out of the leaf. Droplets of 2,4-D at 0.01 µg applied in May caused similar discrete leaf symptoms. Also, 2,4-D at 0.1 µg or more translocated to the shoot tips, where all new leaves had typical 2,4-D symptoms.
- Accepted September 1968.
- Published online January 1968
- Copyright 1968 by the American Society for Enology and Viticulture
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