White blister disease control in radish seed crops
Albugo candida is a significant pathogen of many brassica species causing leaf spotting but, more importantly, hypertrophy of flowering stems (â€œstagheadsâ€) resulting in yield loss. No chemicals are currently registered for white blister control in New Zealand. Little research has been carried out on white-blister management. The implications of seed transmission and subsequent disease expression in radish are not fully understood and control has relied on products containing metalaxyl-m+mancozeb. A range of fungicides were evaluated in two field trials and a pot trial for both efficacy against the disease and effect on radish yield. While metalaxyl-m+mancozeb improved yields in field trials and provided good disease suppression in pot trials, the fungicides azoxystrobin, boscalid+pyraclostrobin and cyazofamid were also equally effective or better than metalaxyl-m+mancozeb. Treatments were able to suppress leaf spotting by up to 90% and inflorescence infection by 50%. Seed yield increases of up to 67% were recorded. Potential new control options for white blister were identified providing alternatives to metalaxyl-m+mancozeb and thus contributing to an anti-resistance strategy.
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