Impact of Shoot Thinning and Harvest Date on Yield Components, Fruit Composition, and Wine Quality of Marechal Foch

Marechal Foch grapevines were subjected to shoot thinning (similar to 15 shoots per meter of row and no shoot thinning) in combination with two harvest dates (early harvest and late harvest) in a factorialized treatment arrangement for two years (2007 and 2008). With shoot thinning, yields were reduced by 3.1 to 7.2 kg per vine and clusters were reduced by up to 59 clusters per vine, while berry weight increased by 0.03 to 0.09 g. Shoot thinning reduced crop load by 4.3 to 7.8 kg yield per kg pruning weight, and increased soluble solids in 2008 by 0.7 to 1.2 Brix. Shoot thinning increased berry anthocyanins by 1.25 to 2.24 mg/g fresh skin weight malvidin-3-glucoside, but no corresponding increase was observed in wine anthocyanins. Delaying harvest resulted in increases of soluble solids (0.5 to 2.3 Brix) and berry anthocyanins (0.32 to 1.48 mg/g) and significantly higher anthocyanins in finished wines. Both late harvest and shoot-thinning treatments resulted in decreased six-carbon alcohols (3 to 33%) in finished wines. The total concentration of tannin in Foch fruit was comparable to that of some vinifera (0.75 to 1.05 mg/berry catechin equivalents). However, the extractability of tannins during winemaking was very low compared to most vinifera (2 to 4%), in part likely due to the low skin tannin concentration. Using a two-alternative forced choice test, panelists reported that later harvest 2008 wines were more fruity than their early harvest counterparts for both treatments and that shoot thinning did not affect fruitiness.