INFLUENCE OF CROP LOAD ON ´CHAMBOURCIN´ YIELD, FRUIT QUALITY, AND WINTER HARDINESS UNDER MIDWESTERN UNITED STATES ENVIRONMENTAL CONDITIONS

The effects of various crop levels on vegetative growth, yield components, fruit composition and winter hardiness of ‘Chambourcin’ grapevines were evaluated in Illinois and Ohio for two and four years, respectively. In the Illinois study, treatments consisted of three pruning levels (15, 20 and 25 nodes retained for each 0.454 kg of dormant prunings) and three cluster-thinning levels (1, 2 and 2+ clusters (no thinning) per shoot in year one and 1, 1.2 and 1.5 clusters per shoot in year two). Treatments consisted of three cluster-thinning levels of 10, 20, and 30 clusters retained per vine in Ohio. As the number of clusters retained per vine increased, yield increased. Total soluble solids and pH of the grape juice decreased as the number of clusters retained per vine increased. As the number of clusters retained per vine increased, the number of ripened nodes and bud cold hardiness (measured as LT50) decreased. There was little interaction between pruning and cluster thinning treatments in both years of the study in Illinois. ‘Chambourcin’ grapevines were most affected by cluster thinning treatments in both states. Crop load varied with vineyard geographical location. It was concluded that ‘Chambourcin’ grapevines grown at a wider spacing and longer growing season in southern Illinois had higher crop load ratios (10 to 14) than those grown at a narrower spacing and shorter growing season in northeast Ohio (4 to 8). INTRODUCTION Crop load, the ratio of crop weight and pruning weight, is a practical and reliable indicator of vine balance status between shoot and fruit production (Bravdo et al., 1984; 1985; Howell, 2001; Naor et al., 2002). Crop load is affected by crop level, which is primarily determined by cluster number per vine and vegetative growth determined by node number per vine, retained after pruning. Kliewer and Dokoozlian (2000) defined wellbalanced grapevines as those that do not overcrop and ripen their fruit to desired soluble solids with a given accumulation of degree-days. They found that optimum crop loads fall within a specific range of 4 to 10 in several Vitis vinifera cultivars. Reynolds et al. (1994; 1995) reported that crop load ratios were higher for the hybrid cultivars, ‘Seyval’ and ‘Chancellor’, than for V. vinifera. This is primarily due to the bud fruitfulness and larger clusters in most hybrids than in V. vinifera cultivars (Reynolds et al., 1986; 1994; 1995). ‘Chambourcin’ is a French hybrid cultivar with fruitful buds and thus it tends to overcrop (Ferree et al., 2003; Pool et al., 1978). It has a higher disease and winter resistance than V. vinifera cultivars, thus it is well adapted to Midwestern and Eastern US environmental conditions. Therefore, ‘Chambourcin’ is desired by grape producers and has emerged as one of the most promising red hybrid cultivar producing quality wine. However, there are no documented reports on the best methods of cropping this cultivar to achieve the highest sustainable yields and desired fruit quality without sacrificing winter survival. The goal of this study was to identify the optimum crop loads of ‘Chambourcin’ that can be recommended to grape producers in the Midwestern US. The specific objectives were to Proc. VII IS on Grapevine