Summary:

Influence of water source on frequency of Phytophthora occurrence was the purpose of this study. Phytophthora spp. was detected in 3 rivers, 2 canals and
2 ponds. Rivers were situated in different part of Poland. Two of them (Jasieniec and Pisia) is following through horticulture areas, whereas Wisła - through area with hardy ornamental nursery stocks. Water canals and ponds are situated nearly or in nursery. Rhododendron leaves baits cv. ‘Nova Zembla' were used for detec-tion Phytophthora in water from March to November. Number of necrotic spots on baiting leaves was the measure of population density of Phytophthora in water. Phytophthora spp. were detected from water from March to November. In canals, the most of necrotic spots on baiting leaves were observed in May and June. In rivers Jasieniec and Rawka and water ponds significantly more necrotic spots on baiting leaves were noticed in March, April, May and in September, October and November. P. cirticola was recovered as the most often occurring species and next P. cryptogea, P. cinnamomi, P. citrophthora, P. taxon Salixsoil.