Epidemiology / Épidémiologie Epidemiology of sclerotinia rot of carrot caused by Sclerotinia sclerotiorum

The epidemiology of sclerotinia rot of carrot was investigated on carrot ‘Cellobunch’ during 1999 and 2000 in Ontario. Apothecia were first detected in the crop in early August to mid-September, after the carrot canopy closed and after 7–11 days with soil matric potentials between –0.1 and –0.4 bars and soil temperatures between 14 and 23 °C. Ascospores were first detected in mid-July to mid-August, usually before apothecia were observed in the crop, and after 7–12 days with soil matric potentials between –0.1 and –0.3 bars and air temperatures between 15 and 21 °C. The numbers of apothecia and ascospores were positively correlated with soil matric potential. Preharvest epidemics started in mid-August to mid-September, after the closure and lodging of the canopy, after the appearance of senescing leaves on the soil and ascospores in the crop, and after rain had initiated 12–24 h per day of leaf surface wetness. Disease incidence was negatively correlated with air and soil temperatures. Postharvest epidemics in storage followed preharvest epidemics in the field, but not all preharvest epidemics resulted in disease in storage. It is suggested that severe epidemics of sclerotinia rot of carrot can occur in storage when disease in the field progresses rapidly and is associated with soil matric potentials of ≥–0.2 bars and leaf wetness of ≥14 h per day, particularly close to harvest. The information revealed in this study contributes to the development of inoculum and disease prediction systems and improved management of sclerotinia rot of carrot.