Evaluation of Strategies for Pruning and Crop Control of Concord Grapevines in Southwest Michigan

Abstract

Seven strategies for pruning and adjusting the crop level of Concord vines were evaluated over a six-year period in a commercial vineyard in southwest Michigan to determine their long-term influence on vine productivity, vine structure, and fruit quality. Manual balance pruning retained 44 nodes per kilogram of cane prunings. Commercial manual pruning resulted in 25% more live nodes per vine and a 19% larger yield than manual balance pruning. Commercial manual pruning resulted in more clusters per meter of canopy but less yield per node, smaller clusters, and lower Brix than vines managed with manual balance pruning. Nevertheless, commercial manual pruning did produce acceptable fruit soluble solids in five out of six years of the experiment. Three severities of mechanical pruning resulted in yields that were comparable to commercial manual pruning at approximately 13 t/ha. As the severity of mechanical pruning treatments decreased, the number of live nodes and clusters per meter of canopy increased while yield per node and average cluster weight decreased. Moreover, the range of annual yields and fruit soluble solids for these treatments became greater as pruning severity decreased. Crop adjustment, applied in combination with mechanical pruning by spraying ammonium nitrate solutions on a portion of the vine at bloom, resulted in lower yields and higher fruit soluble solids than mechanical pruning alone. Fruit soluble solids from treatments involving crop control were greater than the commercially acceptable minimum standard of 15 Brix in five out of six years. Distribution analysis revealed that approximately 90% of the live nodes and clusters for all treatments were situated within the top 60 cm of the trellis. Moderate or minimal mechanical pruning, whether used alone or in combination with chemical crop adjustment, did not provide consistently comparable fruit quality to manual pruning. Severe mechanical pruning produced yields and fruit soluble solids that were similar to commercial manual pruning. The comparable response of these two treatments was due to the compensating factors of a 45% reduction in node fruitfulness and a 75% increase in the number of live nodes for severe hedging when compared to commercial manual pruning. Severe mechanical pruning, when used in combination with cane positioning, manual follow-up pruning after hedging, and shoot positioning, was an acceptable, sustainable practice for managing Concord vines.