New perspectives on the epidemiology and management of phoma stem canker of winter oilseed rape in England

The epidemiology of phoma stem canker (Leptosphaeria maculans) on winter oilseed rape will be discussed in relation to results of experiments comparing fungicide regimes in southern England. Factors affecting the severity of epidemics in England include: 1. The population of L. maculans; A-group and B-group L. maculans differ in ascospore germination, penetration of leaves, leaf spot symptoms and position and severity of stem cankers/lesions. 2. Maturation of ascospores; seasons differ in the timing of ascospore release and phoma leaf spotting, and the subsequent timing and severity of stem canker development. 3. Timing of fu ngicide application; one or two fungicide sprays can give good control of the disease but inaccurately timed applications are ineffective. These results will be discussed in relation to strategies for management of phoma stem canker, including agronomic practices (e.g. sowing date), forecasting severity of epidemics and optimising fungicide use for effective disease control.