Control of light leaf spot of brassicas (Pyrenopeziza brassicaeSutton & Rawlinson) with fungicides

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Abstract
A poisoned-media technique was used to test and rank the efficiency of 23 fungicides in controlling growth of P. brassicae. Tests were done separately using conidia, ascospores and mycelium. Several protectant fungicides strongly inhibited germination of conidia and ascospores. Many systemic fungicides did not prevent spore germination, yet prevented mycelial growth. In field trials with 7 selected fungicides, benomyl + oil, prochloraz and fenapanil gave best control of the disease on cauliflowers. Although there were no significant differences in crop yield between sprayed and unsprayed plots, the presence of scarred petioles on unsprayed plants depressed their market value. In a further trial, benomyl + oil and prochloraz controlled the disease at the 3 rates tested. In a timing of application trial, the first 3 benomyl applications were the most effective, but additional applications further reduced the number of plants with scarred petioles. In both the rate and timing trials, the curds from treated plants were significantly heavier than curds from untreated plants.