RUPESTRIS ST GEORGE, American vine used as a rootstock, also sometimes called Rupestris du Lot or Rupestris-monticola, said to be a selection of V. rupestris Scheele (Dr Richard Smart 2015, p627). It is extremely vigorous, with a long growing season, has excellent resistance to phylloxera, but vines grafted to it can easily overcrop or set poor crops because of extreme vigour and so is not used for high-quality vineyards (Dr Richard Smart 2015, p627).
In California, Dave Koball says that at Bonterra’s Butler Ranch in Mendocino County ‘the Zinfandel is mainly on St George which has a proven track record in Mendocino County.”
In Bordeaux, Rupestris du Lot is declining because its ideal scion, Ugni Blanc, is no longer being planted.
In the Loire, Eric Nicolas of Domaine de la Bellivière says nurserymen dislike Rupestris because it is hard to graft.
Dr Richard Smart in the Oxford Companion to Wine 4th edition ed. Jancis Robinson MW and Julia Harding MW (Oxford University Press, 2015, p627-8.