Activity of cyazofamid against Sclerospora graminicola, a downy mildew disease of pearl millet

Abstract

The efficacy of cyazofamid was tested against pearl millet downy mildew disease caused by Sclerospora graminicola Schroet. Significant inhibition of sporangial sporulation, zoospore release and motility was observed at 0.3 mg mL⁻¹, and this concentration also provided good fungicidal activity under in vitro conditions. Under glasshouse conditions, none of the concentrations tested, either 0.01-2 mg mL⁻¹ as seed treatment or 1-10 mg mL⁻¹ by foliar application, was found to be phytotoxic. The effect of cyazofamid was tested by seed treatment alone, seed treatment followed by foliar application and foliar application alone. Seed treatment with cyazofamid offered only 19.7% disease control, but seed treatment followed by a single foliar application to diseased plants provided good control over disease, seed treatment with two foliar applications was significantly superior and foliar application alone showed a high level of activity, with 10 mg mL⁻¹ giving 97.9% disease control. Lack of systemic activity of cyazofamid was evident, root treatment giving disease levels on a par with the untreated control. The fungicide exhibited strong curative activity, but only moderate translaminar activity, with only marginal (34.8%) disease control after treatment of the adaxial leaf surface at 10 mg mL⁻¹. Loss of cyazofamid activity over time was very low, indicating stable residual and rainfastness activity. These results indicate that cyazofamid has a high potential to be an effective fungicide for the control of downy mildew disease of pearl millet.