EFFECTS OF ESTABLISHED PERENNIAL GRASSES ON YIELDS OF ASSOCIATED ANNUAL WEEDS

Perennial grasses are needed for seeding annual grasslands in the Mediterranean/maritime climatic regime of southwest Oregon. Selection of plants for reseeding purposes would be facilitated by identification of perennial grasses that, once established, are able to suppress resident annual plant production. Perennial grasses were transplanted and allowed to establish in the absence of competition for the first growing season at 2 sites in the foothills of southwest Oregon. After the first growing season, resident annual plants were allowed to reinvade. Perennial grasses such as Berber orchardgrass (Dactylis glomerata L. var. Berber) and Idaho fescue (Festuca idahoensis Elmer) that begin growth early suppressed annuals more effectively than later growing perennial grasses such as intermediate and tall wheatgrasses (Agropyron intermedium (Host.) Beauv. and A. elongatum (Host.) Beauv., respectively). Of the perennial grasses adapted to these sites, those which initiated growth earliest, maintained some growth through winter months, and matured earliest were the best competitors.