Basil downy mildew (BDM), caused by the fungus-like oomycete pathogen Peronospora belbahrii, has become a destructive disease of sweet basil (Ocimum basilicum). Without proper management, BDM can cause complete crop loss. Currently, there are no commercially available sweet basil cultivars with genetic resistance to BDM. Because BDM is a relatively new disease of basil in the United States, there are few currently registered conventional or organic fungicides labeled for its control. Fungicide efficacy trials were conducted in 2010 and 2011 at Rutgers Agricultural Research and Extension Center in Bridgeton, NJ. During both years, seven biological fungicide treatments were field evaluated, including hydrogen dioxide; extract of Reynoutria sachalinensis; Bacillus pumilus strain QST 2808; a mixture of rosemary oil, clove oil, and thyme oil; mono- and dipotassium salts of phosphorous acid; sesame oil; copper hydroxide; and a combination of sesame oil + cupric hydroxide. Six conventional fungicides evaluated included mandipropamid, fluopicolide, propamocarb hydrochloride, cyazofamid, azoxystrobin, and fenamidone. In both years, mono- and dipotassium salts of phosphorous acid provided the best control. Moderate disease suppression was provided by mandipropamid, cyazofamid, and fluopicolide compared with the control in 2010 and mandipropamid, cyazofamid, and copper hydroxide compared with the control in 2011.
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