Management of Powdery Mildew on Flowering Dogwood with Soybean Oil
Deyton, D. E., C. E. Sams, A.L. Cannon, J. C. Cummins, and M. T. Windham.  2011.  J. Environ. Hort. 29(4):185192.

Abstract:
Soybean oil formulations developed in our laboratory were evaluated for control of powdery mildew on flowering dogwood Cornus florida. In a preliminary trial in a field nursery, two formulations, TNsoy1 and TNsoy2 [0, 1 or 2% (v/v)], were sprayed on field-grown flowering dogwood trees at 2 wk intervals from June 10 until August19. Soy oil treated trees had less powdery mildew, higher net photosynthetic rates and more growth than unsprayed trees, without apparent phytotoxicity. Treatments applied the next year in a more frequent rain season did not provide satisfactory control. Newer formulations were developed, primarily using natural-occurring or food grade emulsifiers, and compared to three commercial botanical formulations and to SunSpray Ultra Fine in greenhouse trials. All oil formulations provided some protective and eradicative control of powdery mildew. Photosynthesis of oil treated leaves was usually depressed, compared to controls, for several days but recovered. In greenhouse trials where the oil was not washed off by rain or irrigation, the oil was visible on leaves, reduced powdery mildew severity, and depressed photosynthesis for several weeks. In a second greenhouse trial, soybean formulations provided greater control if applied after rather than before initial inoculation.