SummaryPowdery mildew infection of barley seedlings was significantly reduced using either pre‐inoculation or post‐inoculation sprays of the film‐forming polymers Nu‐Film P, Emerald or Vapor Gard. The greatest reduction in mildew infection was obtained with a pre‐inoculation spray of the polymer Vapor Gard. Although the addition of 1 mmα‐difluoromethylornithine (DFMO) to a 2% solution of Emerald or Vapor Gard resulted in better control of powdery mildew infection than that obtained using the polymer or DFMO alone, the reductions in infection were not significant. Reduction in mildew infection was greatest when the Vapor Gard + DFMO mixture was applied 1 day prior to inoculation with the fungus. Although substantial reduction in mildew infection was achieved using as little as 0.1 mmDFMO with 2% Vapor Gard, or reducing the polymer concentration to 1% in combination with 1 mmDFMO, best control was achieved using 2% Vapor Gard p