`Chambourcin' (Vitis sp.) is a French-American hybrid cultivar that has the propensity to overcrop, and its performance under cool climate and short growing season is not known. This study was conducted for five years (2000 to 2004) to evaluate the effect of three levels of cluster thinning (10, 20, and 30 clusters per vine) on yield and fruit composition of `Chambourcin' grown in northeastern Ohio. Cluster thinning reduced yield per vine and crop load, but increased pruning, cluster and berry weights. Cluster thinning also improved juice composition by increasing soluble solids and pH but not acidity. It was concluded that under the climatic conditions of this study, thinning to 10 clusters per vine (or 8 clusters per meter of row) produced the lowest yield but the highest vine size with the most optimum fruit composition. Therefore, vines from the 10-cluster treatment were considered the most balanced in the 5-year study. Additionally, due to the repeated coincidence of harvest with the first fall frost, it was suggested that the site in continental Northeast Ohio is risky for commercial production and longer and warmer seasons are thus preferred.

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