Cause and Control of Decline of Grapevines in British Columbia. R. S. Utkhede, Research Scientist, Agriculture Canada, Research Station, Summerland, B.C. V0H 1Z0. J. Vielvoye, Grape Specialist, Ministry of Agriculture and Food, Kelowna, B.C., Canada V1Y 4R2. Plant Dis. 68:820-822. Accepted for publication 15 May 1984. Copyright 1984 Department of Agriculture, Government of Canada. DOI: 10.1094/PD-68-820.

Pythium ultimum was the fungus most commonly isolated from grapevines that showed symptoms of decline. In pathogenicity tests, P. ultimum caused severe root rot and death of vines under greenhouse conditions and large lesions on excised twig vines in vitro. Mycelial growth of P. ultimum on cornmeal agar (CMA) was completely inhibited by 50 mg/L of metalaxyl, mancozeb, and a nutrient fertilizer supplement (This), partially inhibited by metalaxyl plus mancozeb, and not inhibited by phosethyl Al. Yield of berries was significantly higher with This treatment in 1982 and with phosethyl Al treatment in 1983. Soil drenches with phosethyl Al around the bases of naturally infected vines showing initial symptoms of decline under vineyard conditions prevented death of grapevines. Metalaxyl or metalaxyl plus mancozeb were ineffective in controlling grape decline and death of vines caused by P. ultimum.