Management of powdery mildew in flowering dogwood in the field with biorational and conventional fungicides

Abstract

In a 2 yr study, control of powdery mildew on flowering dogwood (Cornus florida L.) by four biorational and four conventional fungicides was assessed on seedlings and on 3 yr liners in the field. Biorational fungicides applied were three household soaps containing 0.2% triclosan (Irgasan® DP 300)—Ajax® liquid hand soap, Equate® liquid dish soap and Palmolive® liquid dish soap-and potassium bicarbonate salt. Conventional fungicides applied were propiconazole, thiophanate methyl, azoxystrobin and copper sulfate pentahydrate. All products controlled powdery mildew compared with water controls. Application of the biorational fungicides on a weekly basis was as effective as propiconazole and thiophanate methyl and more effective than azoxystrobin and copper sulfate pentahydrate. Application of some biorational products at semi-monthly intervals was slightly less effective. Of the biorational fungicides, Palmolive® was the most effective but was phytotoxic, whereas Ajax®, Equate® and potassium bicarbonate were not. When three applications of any biorational fungicide were rotated with one application of propiconazole, the incidence of powdery mildew was less than when a fungicide rotation was not included. Plant growth was enhanced with either biorational or conventional fungicides compared with water controls. Propiconazole treatments resulted in the highest growth rates, whereas biorational products were as effective in promoting growth as thiophanate methyl, azoxystrobin or copper sulfate pentahydrate. The incorporation of biorational fungicides in a powdery mildew disease management program may have economic and environmental benefits because they are less costly than conventional fungicides and presumed safer to the environment and the applicators. Key words: Cornus florida L., Erysiphe (sect. Microsphaera) pulchra, Microsphaera pulchra, Oidium spp, Phyllactinia guttata