Evaluation of Biorational Products for Powdery Mildew Management in Cornus florida

Between 1997 and 1999, 21 biorational products were evaluated for powdery mildew control on dogwood seedlings and compared with the traditional fungicides Banner® (propiconazole), ConSyst™ WDG (chlorothalonil and thiophanate methyl) and Cleary's 3336 F® (thiophanate-methyl) in a shadehouse environment. Selected products were also evaluated in rotation with Banner®, where Banner® application was made once for every three applications. Among the biorational products the household soaps, Palmolive®, Ajax®, and Equate®, the potassium bicarbonate salt Armicarb™, and the antitranspirant Vapor Gard® were most effective in reducing powdery mildew severity. However, Vapor Gard® stunted plant growth, and Palmolive® caused some phytotoxicity. While Safer Soap®, M-Pede®, Triact™, Neem Gold®, Kaligreen™, and Ultrafine® oil were not as effective in controlling powdery mildew as the fungicides, the increase in plant growth was similar. Spray regimes that included the biorational and Banner® generally gave better disease control and enhanced plant growth over the biorational products alone. While Banner® and ConSyst™ were highly effective in controlling powdery mildew, Cleary's 3336 F® gave inconsistent results and proved only moderately effective. Overall, plant growth correlated negatively with powdery mildew severity for the biorational products (r = −0.58) and biorational/Banner rotation (r = −0.54).