Additional studies on the chemical control of onion white rot (Sclerotium cepivorum Berk.) in New Zealand

Abstract

Various methods of application of the fungicide procymidone were evaluated for the control of onion white rot (Sclerotium cepivorum Berk.) in field trials carried out in the 1986–87 and 1987–88 crop seasons. The conventional method of seed treatment followed by foliar sprays (monthly × 4) reduced disease incidence by 71 and 95% (of untreated control) in the respective seasons. When applied as a dispersible granule to the soil surface above the seed immediately after planting, disease incidence was reduced by 89 and 95% respectively. Application of procymidone to the soil surface as a spray gave similar control but induced transient symptoms of phytotoxicity in the young seedlings. A slow release formulation of procymidone applied as a seed dressing was more effective than the conventional formulation for seed dressing, and, when followed by foliar sprays, an 85% reduction in disease incidence was obtained. Iprodione applied as a seed treatment followed by four foliar sprays gave a moderate reduction in disease incidence (42%, 60% in respective trials). Procymidone granular formulations are convenient to apply and highly effective against the disease and offer good commercial prospects.

Keywords:

• Allium cepa
• chemical control
• dicarboximides
• iprodione
• onion
• procymidone
• Sclerotium cepivorum
• vinclozolin
• white rot