AbstractThe toxicities of five systemic fungicides benomyl, carbendazim, methyl 4‐(2‐ aminophenyl)‐3‐thioallophanate (NF48), thiabendazole and thiophanate‐methyl and of two non‐systemic fungicides (guazatine and phenylmercury acetate) againstFusarium culmorumwere compared on agar plates; their performance as seed treatments was measured by inoculating the shoot bases of wheat seedlings withF. culmorumin pot experiments. The two most effective compounds, benomyl and thiabendazole, and the less effective thiophanate‐methyl, were evaluated in further seed treatment experiments in which leaf sheaths and roots of slightly older plants were infected. The three fungicides protected the first leaf sheath for more than 5 weeks, but thiophanate‐methyl was least effective. Against root disease, they were effective when infection was mild, but only thiabendazole significantly controlled severe infection. Bioautography confirmed that fungicide levels in shoots were greater after benomyl and thiabendazole, than after carbendazim and thiophanate‐methyl treatments, and that concentrations of fungicide after benomyl, carbendazim and thiophanate‐methyl treatments generally declined between 5‐13 weeks after treatment. Thiabendazole produced a second fungitoxic component detectable in
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