Abstract
'Thompson Seedless' vines were partially defoliated at 12, 35, and 58 days postanthesis (PA). Vines defoliated 25 and 50% at 12 days PA had respectively 28 and 34% lower crop yields whereas vines defoliated the same amount at the two later times did not have yields reduced significantly. Decrease in weight of berries from vines defoliated 12, 35, and 58 days PA ranged from 13 to 36%, 6 to 25%, and 3 to 16%, respectively, at various times during the ripening period. Likewise, total sugar per berry was reduced 6 to 41%, 5 to 43%, and 4 to 26%, respectively. On the basis of total sugar in fruits per vine, the most severe treatment was 50% defoliation at 12 days PA, followed in order of decreasing severity by 25% defoliation at 12 days, 50% defoliation at 35 days, 50% defoliation at 58 days, and 25% defoliation at 35 and 58 days PA. Total acidity and pH of fruits at harvest were not greatly affected by the defoliations.
Total sugar in fruits per vine at harvest was positively correlated with leaf area per vine. About 8 to 10 cm2 of leaf area per gram of fruit was required to mature the crop without decreasing the concentration of sugar in the fruits.
- Accepted February 1970.
- Published online January 1970
- Copyright 1970 by the American Society for Enology and Viticulture