Fungicide resistance of Blumeria graminis f. sp tritici and f. sp hordei populations in the territory of the Czech Republic

In 1994 to 1999, samples of Blumeria graminis f. sp. tritici and Blumeria g raminis f sp. hordei populations were analyzed for resistance to two groups of active ingredients: DMI inhibitors (propiconazole) and morpholines (fen propimorph). Simultaneously standard sensitive isolates of both pathogens w ere tested. Based on comparison of the average level of resistance in the p opulation with the average of standard isolates, mean resistance factors (M RF) were assessed. A higher resistance factor was determined for propiconaz ole than for fenpropimorph in populations of both pathogens. The level of r esistance to these two groups of fungicides is generally low and did not ex ceed the value 13 in any year of investigations. During the study, an even decrease in resistance was observed, particularly to propiconazole. Effects of these changes on the population structure and causes of the resistance decrease are discussed.