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Disease Control and Pest Management

The Adaptability of the Benomyl-Resistant Population of Cercospora beticola in Northern Greece. C. Dovas, Hellenic Sugar Industry S.A., Salonica; G. Skylakakis(2), and S. G. Georgopoulos(3). (2)Eli Lilly S.A., Athens office, Aghia Paraskevi; (3)Department of Plant Pathology, Athens College of Agriculture, Votanikos, Athens 301, Greece. Phytopathology 66:1452-1456. Accepted for publication 11 June 1976. Copyright © 1976 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-66-1452.

In a field comparison of a benomyl-sensitive and a benomyl-resistant strain of Cercospora beticola, the relative proportion of the resistant strain increased after applications of benomyl, benomyl in alternation with triphenyltin hydroxide, or a tank mixture of the two fungicides. The increase in the proportion of the resistant strain was followed by a pronounced reduction of effectiveness of benomyl for leaf spot control. Triphenyltin was equally effective for control of both strains. In the unsprayed control the benomyl-resistant strain appeared more adaptable than the particular sensitive strain with which it was compared. Extensive sampling of leaf spot for three consecutive years after the cessation of benomyl usage for control of C. beticola in Greece showed that the frequency with which benomyl-resistant strains were isolated tended to remain constant for a given area, including fields that were sprayed with triphenyltin fungicides. Thus, the benomyl-sensitive and benomyl-resistant portions of natural populations apparently are equal in fitness for survival under selection pressures imposed by various field conditions.