Managing leaf diseases of carrots with traditional and alternative fungicides including baseline sensitivity studies

Field research was conducted to examine traditional and alternative fungicide options for controlling leaf diseases of carrots caused by powdery mildew and Cercospora. Wet conditions favoured leaf blights caused by Cercospora and dry favoured powdery mildew. Pyraclostrobin, azoxystrobin, and tebuconazole controlled both Cercospora leaf blight and powdery mildew whereas sulphur on its own controlled only powdery mildew compared to untreated plots. Spray oils did not improve powdery mildew control, but when combined with sulphur, improved Cercospora leaf blight control. A baseline sensitivity study indicated a powdery mildew isolate from South Australia, sourced from carrots sprayed with a fungicide containing azoxystrobin over several seasons, was less sensitive to azoxystrobin than an isolate from New South Wales which had not been exposed to the fungicide.