Basil Downy Mildew (Peronospora belbahrii): Discoveries and Challenges Relative to Its Control.

Basil (Ocimum spp.) is one of the most economically important and widely grown herbs in the world. Basil downy mildew, caused by Peronospora belbahrii, has become an important disease in sweet basil (O. basilicum) production worldwide in the past decade. Global sweet basil production is at significant risk to basil downy mildew because of the lack of genetic resistance and the ability of the pathogen to be distributed on infested seed. Controlling the disease is challenging and consequently many crops have been lost. In the past few years, plant breeding efforts have been made to identify germplasm that can be used to introduce downy mildew resistance genes into commercial sweet basils while ensuring that resistant plants have the correct phenotype, aroma, and tastes needed for market acceptability. Fungicide efficacy studies have been conducted to evaluate current and newly developed conventional and organic fungicides for its management with limited success. This review explores the current efforts and progress being made in understanding basil downy mildew and its control.

Evaluation of Fungicides for the Control of Peronospora belbahrii on Sweet Basil in New Jersey.

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.