Potential Organic Fungicides for the Control of Powdery Mildew on Chrysanthemum x morifolium
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University of Washington Abstract Potential Organic Fungicides for the Control of Powdery Mildew on Chrysanthemum x morifolium Chair of the Supervisory Committee: Dr. Sarah Reichard Director, University of Washington Botanic Gardens Michael Bradshaw Powdery mildews are some of the most common plant pathogenic fungi for greenhouse-grown ornamental plants. Millions of dollars are spent annually on fungicides to control these pathogens. There are multiple environmental and human health issues associated with some of the more common fungicides used. These problems dictate a demand for alternative, safe, and environmentally friendly fungicides available on the market. Two fungicide efficacy trials were conducted at the Douglas Research Conservatory at the University of Washington. Four fungicide treatments were evaluated: ammonium oleate, potassium laurate, malic acid, and sesame oil. A popular ornamental plant, Chrysanthemum x morifolium, was inoculated with a species of powdery mildew. The species was identified as Euoidium chrysanthemi at Washington State University Puyallup Research and Extension Center by sequencing its DNA and looking at key morphological features. This was the first case of E. chyrsanthemi recorded on C x morifolium in the United States. Ammonium oleate and potassium laurate inhibited E. chrysanthemi from colonizing C x morifolium and suppressed E. chrysanthemi growth. However, potassium laurate cannot be recommended because it proved to be phytotoxic at the percent concentration tested. Sesame oil was found to suppress E. chrysanthemi growth.
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