Foliar fungicides and their optimum timing reduce sclerotinia stem rot incidence, improve yield and profitability in canola (Brassica napus L.)

Abstract

Sclerotinia stem rot (SSR) caused by Sclerotinia sclerotiorum (Lib.) de Bary causes significant economic losses in canola worldwide. The use of fungicides is an alternative in-field control option for SSR due to a lack of genetic resistance in commercial canola cultivars. The objectives of this study were to evaluate the efficacy and timing of foliar fungicide application for managing SSR, improving seed yield and profitability in canola. Thirteen field trials over eight years were conducted at several sites in Western Australia. In the fungicide effectiveness trials, fungicides were applied as either two-spray applications at 10 and 40% bloom or single application at 30% bloom stages. In the fungicide timing trials, fungicides were applied at various timings including 6–7 leaf, and 10, 30, 50, 60% bloom and late bloom stages. All fungicides evaluated significantly reduced the SSR incidence and improved seed yield in most years except for years of low disease pressure. Among fungicide timing treatments, the fungicides sprayed at between 10 and 50% bloom were more effective compared with earlier or later timing treatments. While both single and two spray regimes were effective, the single spray was more economical. A preliminary analysis based upon the current canola price and cost of fungicide application indicates that a yield increase of 90 kg ha−1 is required to cover the cost of a single spray regime. Yield increases greater than this were achieved in nine out of ten trials that had disease incidence above 5%.