Abstract

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).