Activity of Plant Oils on Diseases Caused by Podosphaera leucotricha, Venturia inaequalis, and Albugo occidentalis. J. Northover, Agriculture Canada, Research Station, Box 6000, Vineland Station, Ontario, Canada L0R 2E0. K. E. Schneider, Agriculture Canada, Research Station, Box 6000, Vineland Station, Ontario, Canada L0R 2E0. Plant Dis. 77:152-157. Accepted for publication 12 October 1992. Copyright 1993 Department of Agriculture, Government of Canada. DOI: 10.1094/PD-77-0152.

The efficacies of several plant oils were assessed with potted seedlings of apple or spinach under controlled conditions, and two oils were orchard-tested. Sunflower, olive, canola, corn, soybean, and grapeseed oils were equally effective in providing over 99% control of Podosphaera leucotricha when applied to apple foliage 1 day before or 1 day after inoculation. Mechanically emulsified canola oil was comparable to dinocap and gave 99% control of P. leucotricha when applied 1, 2, 4, and 7 days after inoculation. The six oils showed only slight prophylactic activity against Venturia inaequalis under controlled conditions. A total of 10 applications of canola or soybean oil emulsified with Agral 90 and applied under orchard conditions reduced foliar and fruit infection by V. inaequalis by 66 and 81%, respectively. However, this level of control was not different from that of the Agral 90 surfactant alone and was inferior to that provided by captan. Peanut and safflower oils and the previous six oils were nonfungicidal to Albugo occidentalis. Refined glyceridic plant oils showed similar activities despite differences in their oleic and linoleic acid compositions.

Keyword(s): apple powdery mildew, apple scab, chlorothalonil, environmentally safe fungicide, organic fungicide, vegetable oil, white rust.