Changes during a three-year period in the sensitivity to ergosterol biosynthesis inhibitors of Sphaerotheca fuliginea in the Netherlands

Abstract

Isolates of Sphaerotheca fuliginea collected in 1981-1984 in cucumber glasshouses in the Netherlands were tested for their sensitivity to the ergosterol biosynthesis inhibitors (EBIs) fenarimol and imazalil.The data collected in the 1981 survey indicated that sensitivity to EBIs was lower than that of reference isolates. In the 1982 and 1983 surveys, sensitivity to EBIs continued to decrease. In 1984, data were collected until July; no significant difference in sensitivity with the 1983 level was apparent.Isolates collected in the district of Limburg, where EBIs were applied less frequently than in the district of Pijnacker, showed a significantly higher sensitivity to EBIs than isolates collected in Pijnacker.Besides differences in sensitivity to EBIs between years, differences within years were noticed. In 1983, the sensitivity to fenarimol and imazalil was significantly higher in the beginning of the growing season, before any fungicides were applied, than later in the growing season.Generally, changes in sensitivity to EBIs did not result in full failure of control. In most cases, a change to shorter spray intervals has been sufficient to compensate for the decrease in sensitivity and to achieve proper control by fenarimol and imazalil. The results once more emphasize', the necessity of designing strategies to prevent resistance to EBIs.

Variation in sensitivity to fungicides which inhibit ergosterol biosynthesis in wheat powdery mildew

“…Other reasons may be the increasing use of fungicides which lack cross-sensitivity (fenpropimorph) and the influx of conidia from refugee areas where sensitive isolates can survive. This situation differs significantly from cucumber powdery mildew control in Dutch glasshouses where an almost continuous selection pressure by EBIs in time led to selection of isolates with gradually higher degrees of resistance in the course of three years (Schepers, 1985). The discontinuous selection pressure in wheat powdery mildew may also explain why the frequency of isolates from Limburg in different sensitivity categories varied over years and during the course of one growing season (Table 2).…”

Acquisition of Resistance to Sterol Demethylation Inhibitors by Populations of Venturia inaequalis

“…c The baseline sensitivity for flusilazole includes six samples from orchard 1 and 2. For difenoconazole, tebuconazole, and pyrifenox, the baseline sensitivity includes one sample from orchard 1. d The efficiency of the fungicide dosage recommended for the field (25,25,75, and 50 mg/liter for flusilazole, difenoconazole, tebuconazole, and pyrifenox). e Fungicide dosage in milligrams/liter needed for 50% efficiency.…”

“…Since DMI fungicides represent single-site inhibitors interfering with C-14 demethylation of 24-methylendihydrolanosterol in ergosterol biosynthesis (6,18), a high risk of development of resistance exists (18). In fact, resistance problems have been observed in several pathogens including powdery mildews (10,11,25), Penicillium digitatum (7), Pyrenophora teres (26), Sclerotinia homoeocarpa (9), and Venturia inaequalis (13). Isolates of V. inaequalis with reduced sensitivities to several DMI fungicides have been reported to occur worldwide (4,13,23,24,31,32).…”

Reduced sensitivity of Cercospora beticola isolates to sterol‐demethylation‐inhibiting fungicides

“…Most references to decreased sensitivity to DMIs are not correlated with reduced performance of the fungicides in the field (Schepers, 1985;Stanis & Jones, 1985;Birchmore & Russel, 1994). Rarely, the decreased sensitivity of a pathogen to a DMI results in failure of disease control (Huggenberger et al, 1984;Hildebrand et al, 1988).…”