Efficacy of Dimethomorph (CME 151) Against Downy Mildew of Grapevines. T. Wicks, South Australian Department of Agriculture, Box 1671, G.P.O., Adelaide, South Australia, 5001. B. Hall, South Australian Department of Agriculture, Box 1671, G.P.O., Adelaide, South Australia, 5001. Plant Dis. 74:114-116. Accepted for publication 11 July 1989. Copyright 1990 The American Phytopathological Society. DOI: 10.1094/PD-74-0114.

Leaf disks removed from sprayed vines were floated on water and inoculated with sporangia of Plasmopara viticola to test the efficacy of dimethomorph against downy mildew of grape. The formation of sporangia was inhibited completely on leaf disks that were inoculated 2, 8, and 15 days after applying dimethomorph at 50, 100, or 200 mg/L. Dimethomorph at 25 mg/L also inhibited the production of sporangia on leaves sprayed 9 days after inoculation. The protective and curative activity of dimethomorph was as good as or better than that achieved with a metalaxyl/mancozeb formulation. Systemic movement from sprayed to unsprayed leaves was demonstrated. Floating of leaf disks was shown to be a useful technique for evaluating downy mildew fungicides on grapes in areas and seasons where natural development of the disease is uncertain.