Estimating Infection Efficiency of Plasmopara viticola on Grape. N. Lalancette, Postdoctoral Research Associate, Department of Plant Pathology, The Ohio State University, Ohio Agricultural Research and Development Center, Wooster 44691. M. A. Ellis, and L. V. Madden. Associate Professors, Department of Plant Pathology, The Ohio State University, Ohio Agricultural Research and Development Center, Wooster 44691. Plant Dis. 71:981-983. Accepted for publication 16 June 1987. Copyright 1987 The American Phytopathological Society. DOI: 10.1094/PD-71-0981.

To estimate the infection efficiency of Plasmopara viticola, the number of sporangia applied to a leaf and the number of zoospores they produced were determined. A relationship was developed between leaf area and the volume of inoculum retained without runoff. Given this relationship and the concentration of sporangia, the number of sporangia applied to a leaf could be estimated. Zoospore production from sporangial suspensions was examined in vitro at various temperatures; an average of seven zoospores per sporangium was observed for incubation temperatures of 5–25 C. Finally, potted vines of Vitis labrusca cv. Catawba were inoculated with sporangial suspensions of different concentrations. Although disease severity increased with inoculum concentration, the infection efficiency was estimated to be about 6% for each treatment.