Synergistic interactions of the fungicide mixture pyrazophos-propiconazole against barley powdery mildew
1991
Zeun, R. (Hannover Univ. (Germany). Inst. fuer Pflanzenkrankheiten und Pflanzenschutz) | Buchenauer, H.
Preinfectional spray treatments of barley seedlings with mixtures of Afugan (a. i. pyrazophos 293 g/l) and Desmel (a. i. propiconazole 250 g/l) in different combinations of concentrations always showed at least additive effects against disease incidence of Erysiphe graminis f. sp. hordei. Following postinfectional applications, the effectiveness of propiconazole could be increased synergistically by the addition of pyrazophos. The Desmel-Afugan synergism was evident at reduced application rates of the fungicides, postponed application times and reduced Desmel sensitivity of barley powdery mildew isolates. Afugan as well as the active ingredient pyrazophos or its formulation displayed synergistic effects in mixtures with Desmel. The application of the active compound propiconazole instead of Desmel lead to similar results, especially the mixture with pyrazophos remarkably increased the fungicidal effects. Besides the number of pustules per leaf, the size of the pustules and the conidia production were reduced drastically by Afugan-Desmel mixtures. Histological studies showed that 2 days after inoculation the number of incompletely developed or damaged primary haustoria was higher in seedlings treated with the fungicide mixture compared to the single fungicide treatments. Four days after inoculation, mycelial growth was reduced more efficiently on Afugan-Desmel-treated plants than by the most effective single treatment of Desmel. While the single applications of Afugan and Desmel only caused a reduction in the number of secondary haustoria, the mixture completely prevented the development of secondary haustoria
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