The influence of cluster exposure to sunlight on fruit composition of 'Norton' grapes was studied. Three exposure levels, such as fully exposed, partly exposed, and fully shaded, were established by canopy management practices, such as shoot positioning, shoot thinning, and leaf removal. Row orientation significantly impacted fruit composition with east west orientation and resulted in high total soluble solids, anthocyanin, and tannin content. Titratable acidity, total phenol, and juice potassium was highest in vines planted in north south row orientation. Fully shaded clusters had the lowest total soluble solids, lower glucose and fructose content, and highest juice potassium and malic acid content. Fully exposed clusters displayed lowest titratable acidity. Fully exposed clusters on the west and south side of the canopy received photosynthetically active radiation of more than 1,100 µ mole m -2 sec -1 , while partly exposed and fully shaded clusters received less than 10% of total photosynthetically active radiation at solar noon. Berries on fully exposed clusters exhibited a temperature that was about 10-15 • F higher than air temperature, while fully shaded clusters were about 1-2 • F higher than air temperature.
Balanced, dormant hand pruning was compared with minimal and machine box-cut pruning with no fruit thinning, thinning at 27 to 45 days postbloom, or thinning at veraison on Vitis labruscana grape cultivars, Concord and Sunbelt. Weekly berry weights measured during the growing season showed that minimally pruned ‘Concord’ and ‘Sunbelt’ generally had lower berry weights than hand-pruned vines. Lag phase occurred 50 ± 7 days postbloom in ‘Concord’ and 58 ± 7 days postbloom in ‘Sunbelt’. The duration of harvest period was longer for ‘Concord’ than ‘Sunbelt’, and minimally pruned vines without thinning had the most delayed ripening regardless of cultivar or time of fruit thinning. The desired soluble solids of 17% for ‘Concord’ and 18% for ‘Sunbelt’ were achieved without differences in other fruit composition parameters on all treatments. Delaying harvest of minimally pruned vines without thinning by about 7 days was required to achieve the desired soluble solids. Pruning methods had more effect on yield components than time of thinning. At harvest, minimally pruned vines had lower cluster weights, berry weights, and yield per node compared with hand pruning in both cultivars and years. In terms of second year yield response, ‘Sunbelt’ was not as detrimentally impacted by machine and minimal pruning without thinning compared with ‘Concord’. Preliminary results indicate that machine and minimal pruning with and without thinning are viable alternatives to hand pruning for ‘Concord’ and ‘Sunbelt’ grapes in irrigated vineyards with warm, long growing seasons.
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