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Canopy management and ethephon application (100 mg·liter-1 2 weeks after veraison) were investigated for 2 years as possible ways to improve color and overall quality of `Reliance' grapes (Vitis spp.). Canopy management consisted of leaf removal, shoot positioning, and cluster thinning. Grapevines were subjected to one of two levels of leaf removal and one of two levels of preharvest ethephon spray and were either thinned to a basal cluster or nonthinned. Thinning and ethephon advanced harvest dates by 5 to 8 days and 2 to 3 days, respectively. In 1989, berry weight was increased by thinning but was not affected by leaf removal or ethephon. Leaf removal (direct sun exposure) of thinned and nonthinned treatments increased “L” values (lighter colored fruit) in 1989. In 1990, leaf removal, ethephon, and thinning resulted in higher “L” values. The “a” values were significantly increased by leaf removal in 1989 and 1990 and by thinning in 1989, a result indicating increased skin redness. Exposed clusters of nonthinned treatments had significantly higher “b” values due to more yellow fruit in 1989 than in 1990. Ethephon increased “b” values in thinned and nonthinned treatments. In 1990, leaf removal increased “b” values. Thinning resulted in more evenly colored, redder fruit. Leaf removal caused a lightening and yellowing of the skin. Juice from leaf removal treatments in 1990 had significantly higher “L”, “a”, and “b” values. Ethephon significantly increased the “a” value of juice in 1989, and leaf removal significantly increased the “b” value in 1989. The percent soluble solids of juice was generally decreased by ethephon and increased by leaf removal and thinning. Titratable acidity was decreased by leaf removal and ethephon and increased by thinning in both years. Leaf removal decreased berry pH in 1990. Thinning increased coloration, and direct exposure to light decreased coloration. The results with ethephon were not conclusive. Chemical name used: 2-chloro-ethyl-phosphonic acid (ethephon).
Grape clusters were subjected to one of two levels of leaf removal, one of two levels of preharvest ethephon spray, and either thinned to a basal cluster or left unthinned. Ethephon was applied at a concentration of 100 ppm two weeks after veraison. Affects on soluble solids content (SSC), titratable acidity (TA), pH, hue, chroma, and L, a, b values were not consistent. In 1989, light exposed clusters of thinned vines had significantly higher SSC. In 1990, when ethephon was applied to non-thinned vines, light-exposed clusters had higher SSC values than non-exposed clusters. Light, ethephon, or thinning in 1989 and light or ethephon in 1990 significantly increased TA. Ethephon in 1989 and light in 1990 significantly higher pH in 1989, and ethephon-treated clusters from thinned vines had significantly lower pH in 1990. Juice from light treatments in 1990 had significantly higher L, a, b, and chroma values. Ethephon significantly increased the “a” value of juice in 1989, and light significantly increased the “b” value. Hue was significantly different for light and ethephon treatments in 1989.