ARS | Publication request: Oregon 'Pinot noir' grape anthocyanin enhancement by early leaf removal

Submitted to: Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 7, 2013
Publication Date: March 15, 2013
Citation: Lee, J., Skinkis, P.A. 2013. Oregon 'Pinot noir' grape anthocyanin enhancement by early leaf removal. Food Chemistry. 139:893-901.

Interpretive Summary: ‘Pinot noir’ grapes are a high value crop in Oregon. Oregon winegrape growers start removing leaves anytime between fruit set and véraison (onset of ripening) with the assumption that this management practice will improve microclimate around the cluster, prevent pest incident/severity, improve spray permeation, and reduce the amount of pesticide used. However, there are direct and indirect consequences on vine growth and berry quality due to this practice. We were the first to demonstrate that if Oregon winegrape growers desire to reach high berry pigment levels, they should remove leaves at bloom and maintain a free leaf zone up until harvest. Other fruit maturity indices were not altered by early leaf removal.

Technical Abstract: Complete cluster zone leaf removal of ‘Pinot noir’ was initiated at three separate pre-véraison growth stages (bloom, grain-pea size, and bunch closure) and maintained leaf free until harvest for four growing seasons (2008-2011). Fruit anthocyanin composition was examined at harvest for the last two vintages (2010 and 2011) and compared to a control- no cluster zone leaf removal. Experiments were conducted at two commercially operating Oregon vineyards (site A= 420 rootstock/‘Pinot noir’ 115 scion and site B= 3309C rootstock/‘Pinot noir’ 777 scion). All clusters contained the five anthocyanins typically found in ‘Pinot noir’. Leaf removal at bloom and maintained until harvest produced maximum anthocyanin accumulation in ‘Pinot noir’ grapes (site A= 85.24 mg/100 g and site B= 125.06 mg/100 g), compared to no leaf removal (control; site A= 57.91 mg/100 g and site B= 97.56 mg/100 g). Even leaf removal at bunch closure (last leaf removal initiation period) increased grape anthocyanin (site A= 73.22 mg/100 g and site B= 118.93 mg/100 g) compared to control, but total anthocyanins were lower than grapes from bloom leaf removal (first time period). Results differed slightly by vineyard site and rootstock/scion combination.