Development of Resistance to Metalaxyl in Pseudoperonospora cubensis. M. Reuveni, Department of Life Sciences, Bar-Ilan University, Ramat Gan, Israel. H. Eyal, and Y. Cohen, Department of Life Sciences, Bar-Ilan University, Ramat Gan, Israel. Plant Dis. 64:1108-1109. Copyright 1980 American Phytopathological Society. DOI: 10.1094/PD-64-1108.

A metalaxyl-resistant strain of Pseudoperonospora cubensis was isolated in December 1979 from cucumber plants growing in plastic houses on the northern coastal plain of Israel. Plants at the two-leaf stage, drenched with 15 mg (a.i.) of metalaxyl per 0.5-L pot or sprayed with 500 µg per leaf, became heavily mildewed when inoculated with the resistant strain, but 50 µg/0.5-L pot or 25 µg per leaf effectively controlled the disease in plants inoculated with the sensitive strain. Both strains of the pathogen had the same physiologic specialization when introduced on six members of the Cucurbitaceace.