Application strategies for control of onion white rot by fungal antagonists

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Abstract
The fungal species Chaetomium globosum, Coniothyrium minitans, Trichoderma harzianum, T. koningii, and T. virens were confirmed as antagonists of Sclerotium cepivorum, the causal agent of onion white rot in two glasshouse trials. In Trial 1, all fungal treatments afforded disease control equivalent to the fungicide procymidone (1 g a.i./ 100 g seed) when applied to the soil as a soil additive (sand:bran:fungal mix, 1:1:2) at the time of planting. Applications of T. harzianum (C52) and T. koningii (C62) significantly reduced disease incidence from 39.8% in the control to 7.7 and 5.4%, respectively. When treatments were applied 2 weeks before planting, only T. harzianum (C52) gave disease control equivalent to the fungicide. In Trial 2, disease incidence was significantly less when T. harzianum (C52, D73) and T. virens (GV4) were applied as soil additives at planting (34, 40, and 43.1 %, respectively) compared with that in the control treatment (66.5%) 8 weeks after planting. However, disease control declined as Trial 2 progressed with over 95% of the plants infected in all treatments at trial completion. Strategies for field application of the best biological control agents for control of onion white rot are discussed.