Basil downy mildew: Now a widespread problem across the region
Posted: June 26, 2014
Characteristic yellowing delineated by the leaf veins. Sporulation on the underside of the leaf shown in the photo below. Photos: Meg T. McGrath
Since 2009, basil downy mildew has become an increasing problem. Often the initial symptoms, which consist of a general yellowing of the leaves, are confused with a nutritional problem. Similar to other downy mildews, purplish-gray sporulation will develop on the underside of the leaf. It is now considered widespread and is suspected to have arrived in the U.S. on contaminated seed since it is known to be seedborne. However, the pathogen can be transported long distances in the wind trajectories similar to cucurbit downy mildew. During the growing season, maximizing air circulation around the plants and fungicides are the primary management tools. Unfortunately fungicides need to be applied preventatively to be most effective and often only offer suppression at best. In conventional production, Quadris, Armicarb, Ranman and phosphorus acid products can be used (the latter two have been most effective in research trials) and for organic production Actinovate AG, Double Nickel 55, MilStop, Regalia, Trilogy and OxiDate are OMRI-approved for the suppression of downy mildew.
Additional information about basic downy mildew can be found in a more comprehensive article written by Dr. Meg McGrath from Cornell.
Basil downy mildew lower leaf sporulation (Photo: Meg T. McGrath)