Effective Downy Mildew Management in Basil Using Resistant Varieties, Environment Modifications, and Fungicides

Considerable progress has been made in managing Peronospora belbahrii, an oomycete pathogen that causes basil downy mildew, since 2007, when it was first detected in the United States. Conventional fungicides have been registered and shown effective against P. belbahrii in replicated experiments in recent years. Unfortunately, because of their specific modes of action and P. belbahrii biology, some are at risk for resistance development, which has been documented outside the United States. Sweet basil varieties have been developed and commercialized, with most exhibiting good to high levels of resistance to basil downy mildew. Knowledge about conditions favorable for infection and disease development has resulted in the identification of cultural practices for managing basil downy mildew in the greenhouse. Practices being implemented include fans to move leaves, thus preventing water deposition and decreasing relative humidity, lighting at night to mitigate sporulation, and temperature modification to suppress disease development. Although downy mildew can be more effectively managed today, growers still experience losses, particularly when conditions are highly favorable for disease development. None of the organic fungicides or programs tested have provided adequate control for susceptible varieties, and limited testing has been done on resistant varieties to date. This review aims to summarize effective basil downy mildew management tools, in particular downy mildew-resistant varieties, environment modifications, and fungicide applications.