THE PERIOD OF SUSCEPTIBILITY OF ULMUS AMERICANA TO CERATOCYSTIS ULMI UNDER CONDITIONS PREVAILING IN QUEBEC

Abstract

The results of an experiment performed for the first time in 1946 and repeated the next 3 years shows that proneness of 10- to 13-year-old white elms to infection by C. ulmi was high from May 15 to late July in Quebec. However, successful inoculations were obtained each year on trees inoculated before and after (as late as November) that period. The time at which susceptibility reached its maximum, which was some time between the end of May and late June, depended on weather conditions. Wilting was suppressed during periods of dry weather.