Summary:

The relationship between weather conditions and most important economi-cally infectious diseases of assimilative apparatus of forest trees was investigated for stands up to 20 years old. The analyses were based on data of Scots pine needle cast, twisting rust, shoot dieback, oak powdery mildew occurrence in Poland from the years 1975-2004 and meteorological data from 30 stations located all over the country from the years 1966-2005. There were 130 meteorological parameters of air and soil temperature, precipitation, humidity, synthetic hydrothermal coefficients (in forms of monthly, seasonal, annual and multi-annual means) as well as their deviations from multi-annual averages used in the calculations. To determine most influential for disease occurrence weather variables correlation and principal component analyses were applied, while multiple regression analysis was used to determine the dependence between diseases occurrence and selected weather parameters. For all analyzed diseases statistically significant dependence was found, most pronounced for meteorological parameters of the year of disease appearance as well as from one-two years earlier.