ISHS Acta Horticulturae 179: V International Symposium on Growth Regulators in Fruit Production
THE EFFECTS OF N-(2-CHLORO-4-PYRIDYL)-N'-PHENYLUREA AND THE 3-CHLOROBENZYL ESTER OF DICAMBA ON THE GROWTH AND SUGAR CONTENT OF GRAPES |
| Author: | Louis G. Nickell |
| DOI: | 10.17660/ActaHortic.1986.179.135 |
| Abstract:
N-(2-chloro-4-pyridyl)-N1-phenylurea (CPPU) is a plant growth regulator of the cytokinin type which shows potent cytokinin activity in the tobacco callus tissue culture test. Its activity range is from less than 1 to 200 ppm on a number of plants according to the method of application, the type of response desired, the developmental stage of the plant or crop at time of application, and other variables. It inhibits flower shedding in grapes and other crops; increases the size of grapes and other fruits; and increases the yield in a number of crops including melons, kiwi fruit, potatoes, tomatoes, and peppers. The chemical is a white solid with a solubility in water of approximately 65 ppm. It has an extremely low order of toxicity both to plants and to animal systems. For example, the acute dermal toxicity in rabbits is > 2,000 mg/kg. When applied to grapes at pre-bloom and during bloom it causes a high percentage of berry set. This percentage decreases in the post-bloom period. The effect on berry size is almost the opposite of that of berry set - there being little effect at the pre-bloom, a slight effect at bloom, and a significant effect in post-bloom. When bunches are dipped in solutions from 2 to 10 ppm there can be up to a doubling in size of the individual berries. When CPPU is applied by commercial sprayers as used in commercial vineyards at a gallonage of approximately 300 gallons/acre, the maximum effect shifts to 5 to 20 ppm because of a decrease in efficiency of application. Another important aspect for table grapes is the strong tendency of the berries to stay on the bunch post-harvest - a problem commonly found in packing, shipping, and storage of table grapes. Most of this work has been done with Thompson Seedless grapes. However, similar results have been obtained for the red-seeded grape Carignane, the seedless red grape Flame, and other varieties. The 3-chlorobenzyl ester of dicamba (CBED) has been shown to increase the sugar content of a number of grape varieties when applied at levels of 0.5 to 2.0 ounces of active ingredient per acre at from 2 to 8 weeks before harvest. Although this material has slight herbicidal properties when tested at much higher levels, at the levels used to increase the sugar content of grapes, no phytotoxicity was observed. Again, the bulk of the work has been carried out using Thompson Seedless and Carignane; positive results have been found for Chardonnay, Cabernet Sauvignon, and Sauvignon Blanc. Preliminary toxicology studies show CBED to have a low order of toxicity in both dermal and oral studies. | |
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