2017 ASHS Annual Conference

New cold-hardy wine grape cultivars have expanded possibilities for grape growers and vintners beyond the selections traditionally available to the Midwest in years past. With these emerging cultivars, various cultural practices should be examined to study how they can influence grape quality at harvest. Practices related to leaf removal or canopy leaf thinning are quite common in established grape growing regions as well as fruit thinning or cluster removal. To better understand how new cold-hardy grapes respond to these traditional canopy management techniques, two experiments were conducted at Iowa State University’s Horticulture Research Farm. In 2015 and 2016, vines trained to a single-curtain bilateral cordon system were thinned to retain no more than 5 shoots per foot of cordon. ‘Marquette’ and ‘La Crescent’ vines were divided into two canopy management groups: leaf removal or cluster removal. Leaf removal consisted of removing leaves adjacent to and below the second cluster, and removing leaves adjacent to and below the first and second cluster. Cluster removal consisted of removing all clusters except the primary cluster and removing only the tertiary clusters (leaving the primary and secondary clusters). In addition, there were two control groups: no leaf removal or cluster removal. At harvest, fruits were collected, weighed for overall yield, and either a 50-berry subsample (2015) or 5-cluster subsample (2016) were collected to analyze fruit quality characteristics [°Brix, pH, and titratable acidity (TA)]. ‘Marquette’ and ‘La Crescent’ fruit quality was similar regardless of treatment in 2015 as well as ‘Marquette’ in 2016. ‘La Crescent’ did show an improvement in fruit quality (°Brix and TA) during the 2016 season on vines that had both the secondary and tertiary clusters removed but a significant reduction in average yield (5.1 kg) was also apparent compared to untreated vines (8.0 kg). Even though leaf removal did not positively impact fruit quality on ‘Marquette’ vines, the practice may have secondary benefits related to increased light penetration and a faster drying of fruit, which could help reduce disease pressure. Variable results were apparent with cluster removal techniques on ‘La Crescent’ vines when comparing 2015 and 2016 results, but overall yield may have a greater influence on fruit quality at harvest. It will be important for grape growers to understand site dynamics and vine characteristics to determine if they should implement cultural practices aimed at improving overall fruit quality.