Leafroll (Red-Leaf or Rougeau) and Its Effects on Vine Growth, Fruit Quality, and Yields

¹ Crops Research Division, A.R.S., U.S.D.A., Department of Plant Pathology, University of California, Davis, California.
² Department of Viticulture and Enology, University of California, Davis, California.

Transmission experiments indicate that the disorder known as red leaf in California and variously as rougeau, flavescence, or brunissure in France is probably grape leafroll.

Leafroll causes affected vines to develop more slowly than healthy vines. It causes fruit sugar at harvest to be generally lower than that from healthy vines. This difference is not apparent in early summer. In unirrigated vineyards yields are about one third of those of healthy vines. Wood production is also reduced, and fruit clusters are fewer and smaller.