Occurrence of downy mildews on ornamental plants and their control by chemical compounds.

The downy mildew on Coreopsis grandiflora caused by Plasmopara halstedii was observed during summer, mainly in July and August. Symptoms of the disease were first seen on external leaves and progressively spread to inner parts of plant rosette. On Alyssum saxatile downy mildew symptoms induced by Peronospora parasitica were observed during whole vegetation period with the strongest expression in early spring and late summer. Amistar 250 SC (25% azoxystrobine), Mildex 711,9 WG (66.7% phosethyl aluminium + 4.4% fenamidone), Previcur Energy 840 SL (530 g/l propamocarb + 310 g/l phosetyl aluminium) and Tanos 50 WG (25% cymoxanil + 25% famoxate) were used for pathogens control. In the protection of Coreopsis grandiflora against P. halstedii all tested compounds, applied curatively, decreased sporulation of the pathogen. On treaded plants at least 4-time less leaves were diseased. In the control of P. parasitica on Alyssum saxatile, the smallest number of swallowed structures on leaves was noticed on plants treated with azoxystrobine at conc. 250 microg/cm3.