Effect of Foliar Uptake of Azoxystrobin and Kresoxim-methyl on Fungicidal Activity against Cucumber Powdery Mildew

Azoxystrobin applied by aqueous WP suspension 50 mg/l was slightly absorbed into cucumber leaf in the absence of activator surfactant 24 h after spraying, but was increased to 25.7% by adding polyoxyethylene monohexadecyl ether (12 moles of ethylene oxide, CE-12) 500 mg/l Only 4.1% of kresoxim-methyl WDG 100 mg/l in the absence of surfactant was absorbed into cucumber leaf 24 h after spraying, but was increased to 58.0% by adding polyoxyethylene monooctadecyl ether (14 moles of ethylene oxide, SE-14) 1,000 mg/l The effect of CE-12 500 mg/l on foliar uptake of kresoxim-methyl at 50 mg/l was twice bigger than on azoxystrobin. Fungicidal activity of azoxystrobin WP against cucumber powdery mildew was marginally increased by adding surfactants to facilitate foliar uptake of azoxystrobin, so that the further increase of azoxystrobin uptake into cucumber plant by the addition of adjuvant was not a practical mean for enhancing the formulation efficacy in view of fungicidal activity. It was not possible for kresoxim-methyl to assess the adjuvant effect on the fungicidal activity in a greenhouse trial due to the vapor effect of active ingredient.