Managed Canopies of Norton Grape Reduced Juice Acidity and Berry Rot

Norton (Vitis aestivalis Michx) is a vigorous grape cultivar with a dense canopy.  The fruiting zone is often shaded resulting in poor juice quality.  A horizontally divided canopy will reduce shade; however, Norton is often grown as a non-divided vertical canopy in Missouri because of its suitability for mechanical harvest.  In several studies, Norton canopies were managed by manually positioning shoots, and removing leaves and summer lateral shoots.  All treatments decreased canopy density and increased sunlight penetration.  In 2010, yield per vine, average cluster weight, and juice soluble solids, pH and potassium were not significantly different in managed versus unmanaged vines.  Cane pruning weight and juice titratable acidity decreased in managed vines.  In 2011, similar results were found.  This could be advantageous, because Norton grape has high acidity in most harvest years.  It was noted that late season berry rot also decreased in managed vines.  In 2012, yield per vine, average cluster weight, and juice soluble solids, pH, potassium and malic acid were not significantly different in managed versus unmanaged vines.  Much like in 2010-11, cane pruning weight and juice titratable acidity decreased in managed vines.  Finished wine made from the grapes of managed vines showed no significant differences although a trend toward a decrease in pH and potassium and an increase in total anthocyanin was noted in 2010 and 2012.  Leaf and summer lateral removal were equally effective at decreasing canopy density in Norton vines.  Leaf removal often showed greater effect and it was faster to implement.  A combination of both leaf and summer lateral removal could result in fruit sunburn.