CALCULATION OF THE INCUBATION PERIOD OF POWDERY MILDEW UNDER FIELD CONDITIONS

The influence of climatic conditions on the incubation period of Erysiphe gr aminis on winter wheat was studied in two field trials in connection with the development of a mathematical model for the prognosis of infection probability by powdery mildew. The longest incubation period assessed on the artificially infected upper leaves of the canopy was 14, the shortest almost 6 days. By means of hourly canopy temperatures together with the presented temperature optimum curve (optimum 22 degrees C, maximum 26.5 degrees C), it is possible to calculate the incubation period adequately, 82 % of the values deviate less than 1 day from the measured data. According to the temperature optimum curve, the incubation period of the pathogen on field plants amounts to almost 4 days under optimal conditions. This can be explained by the greater resistance of the inoculated plant tissue compared with that of greenhouse planes or primary leaves. When successfully infected planes suffered from draught, incubation periods approximately 1 day longer than expected (calculated) were noted.