MODELING THE INFLUENCE OF WINTER FROSTS ON THE DEVELOPMENT OF THE STEM CANKER OF RED OAK, CAUSED BY PHYTOPHTHORA-CINNAMOMI

The evolution of trunk cankers induced by Phytophthora cinnamomi over a period of about 25-30 years was studied by a dendrochronological met hod on 20 Quercus rubra trees located in four plots in southwest Franc e. In plots as far from each other as 150 km, AE(i), the annual evolut ion of the cankers, presented similar trends, with enlargement or redu ction of the cankers occurring in the same years. This suggests a stro ng influence of climatic conditions on the disease development. A mode l describing the influence of winter frost on the evolution of the can kers was developed. This model predicted the AE(i) well. No trace of P cinnamomi lesions could be found in the growth ring of an individual tree in years for which the model predicted total elimination of the f ungus. Moreover, the amount of lesions induced by P cinnamomi on the t rees studied usually decreased in years for which the model predicted poor survival of the fungus.