The Effects of Temperature on the Incubation and Latent Periods of Powdery Mildew (Erysiphe polygoni) on Clematis

The e€ects of temperature on the length of the incuba- tion and latent periods of clematis powdery mildew, caused by Erysiphe polygoni, were studied. At constant temperatures over the range of 10±29°C, the length of the incubation period ranged from 4 to 11 days, and the length of the latent period ranged from 4 to 13 days; no visible colonies developed at 30°C after 19 days. The relationship between temperature and the rates of fungal development within the incubation and latent periods (expressed as the reciprocal of the lengths of the incubation and latent periods) under constant tempera- ture were described well by a non-linear model. The resulting curves were not the usual form of an asym- metrically bell-shaped type; instead, they were of expo- nential type with the development rate increasing with increasing temperatures. The relationship between tem- perature and the development rate during the post- incubation (before sporulation) period was non-linear with an optimum temperature of approximately 20°C