ISHS Acta Horticulturae 80: Symposium on Growth Regulators in Fruit Production
THE DEVELOPMENT OF ETHEPHON'S THINNING POTENTIAL FOR SPUR ‘DELICIOUS’ APPLES |
| Author: | C.R. Unrath |
| Abstract:
Initial evaluation of Sevin and Sevin-NAA combinations showed them to be ineffective in thinning spur 'Delicious' at rates which did not result in fruit nubbining. Thus, an obvious need existed for determining ethephon's (2-chloroethylphosphonic acid) potential as a thinner. Early screening of ethephon's thinning activity showed maximum response at about 2 weeks after petal fall; this activity was determined to be more closely associated with fruit size of 10–11 mm than with days after petal fall. Hand gun applications of 300–400 ppm thinned effectively. However, these same rates were ineffective when applied as air blast applications. The effectiveness of air blast applications was related to the rate of water application. Ethephon-NAA combinations were found to be more effective than ethephon alone. When rates of water application were adjusted to the tree row volume (TRV) of each orchard, thinning activity of Sevin-NAA, ethephon-NAA and Sevin-ethephon combinations was found to be substantial and very uniform across locations. It appears that further refinement in water application rates relating to tree foliage density and in air blast sprayer nozzle distribution may be needed before consistently reliable thinning activity is obtained with any spur 'Delicious' chemical thinners. | |
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