Use of demethylation inhibiting fungicides (DMIs) for the control of onion white rot (Sclerotium cepivorum Berk.) in New Zealand

Abstract

The demethylation inhibiting (DMI) fungicides, tebuconazole and triadimenol, both of the triazole group, were evaluated for the control of white rot (Sclerotium cepivorum Berk.) on onion (Allium cepa L). Both fungicides, applied as foliar sprays, gave a high degree of white rot control, effecting reductions in disease of up to 85% ofthat in untreated plots. When applied as a soil surface spray immediately after sowing, tebuconazole provided a high level of protection all season. The greatest degree of control was obtained from a combination of seed treatment with procymidone (a dicarboximide fungicide), followed by foliar sprays of either procymidone, tebuconazole, or triadimenol. Tebuconazole was unsuitable for seed treatment, causing high seed and seedling mortality. For maximum control of white rot, a combination of seed treatment and foliar sprays should be used. The triazoles—tebuconazole and triadimenol are suitable alternatives to procymidone for foliar sprays.

Keywords:

• Allium cepa
• chemical control
• dicarboximides
• onion
• procymidone
• Sclerotium cepivorum
• triazoles
• tebuconazole
• triadimenol
• white rot