Basil downy mildew has been reported for the first time this season near Millville, NJ in potted Thai and Cinnamon basil plants being sold at big box stores, as well as in sweet basil located in grower field. All basil growers in New Jersey should scout their fields on a daily basis.
All sweet basils are susceptible to the disease. Lemon/Lime and Spice-type basils show much greater tolerance/resistance to basil downy mildew. Control of basil downy mildew begins with planting resistant-types (when possible) and preventative fungicide applications BEFORE basil downy mildew appears on your farm. Weekly applications of a phosphite fungicide (FRAC code 33) such as K-Phite, Pro-Phyt, Rampart or other labeled phosphite at a high rate will help suppress basil downy mildew development. Ranman (cyazofamid, 21) at 2.75 to 3.0 fl. oz/A and Revus (mandipropamid, 40) at 8.0 fl. oz/A now have labels and will also help to suppress basil downy mildew development. These fungicides should be used in rotation with each other and included in a tank mix with a phosphite fungicide on a weekly basis. Our research has shown that if fungicide applications are started AFTER the pathogen has been found in the field will often result in very poor season-long control.
Options for organic growers are limited. Our research has shown that most products only offer some suppression as long as disease pressure remains low. Avoid overhead irrigation if possible, increase plant spacing to improve airflow to help leaves remain dry, and always plant basil in a sunny location.
Please remember, all abandoned basil fields should be sprayed with gramoxone or disked under immediately after last harvest to kill the foliage! Abandoned fields left unattended after use will only serve as a source of inoculum for other fields.
If you suspect basil downy mildew on your farm, please contact your county agent.