Minimal Input Production Systems Affect Yield and Juice Quality of 'Sunbelt' Grapes in California's San Joaquin Valley

Abstract

'Sunbelt' is a juice grape cultivar developed by the Univ. of Arkansas. This cultivar produces 'Concord'-type juice and is adapted to warm climatic conditions of the southern United States. Preliminary evaluation showed that 'Sunbelt' has potential to produce high-quality juice under the hot climatic conditions of the San Joaquin Valley. A study was conducted during the 1998 and 1999 growing seasons to further evaluate the adaptation of 'Sunbelt' to the San Joaquin Valley and determine the response of this cultivar to selected pruning methods. Vines were grown for two seasons without use of insecticides, fungicides, or herbicides. Vines were subjected to four pruning treatments: severe hand pruning (60-80 nodes retained/vine); moderate hand pruning (120-160 nodes retained/vine); machine pruning with hand follow-up (160-180 nodes retained/vine); and minimal pruning (200-400 nodes retained/vine). Vines were trained to a Geneva Double Curtain trellis system. Yield, components of yield, and juice quality were significantly impacted by pruning treatment. In both seasons, mechanized systems of pruning (machine and minimal) produced higher yield than hand pruning. Minimal pruning resulted in the highest yield (42 t·ha-1) in 1998, while yield from the machine-pruned vines was highest (29 t·ha-1) in 1999. Minimally pruned vines had the highest clusters/vine and lowest cluster weight among the treatments. The extremely high yields obtained for the minimal pruning treatments produced fruit that was less mature resulting in juice with lower soluble solids than the other treatments in 1998. However, in 1999 the juice from minimally pruned vines had the highest soluble solids. Sensory analysis of juice produced in 1999 showed that the juice from the machine-pruned treatment had the least color intensity. Sensory analysis showed that minimal and severe hand pruning were ranked higher for sweetness than machine and moderate hand pruning. In the second year of the study, the juice from the minimal-pruned and severe hand-pruned treatment were preferred over the moderate hand-pruned treatment or the machine-pruned treatment.