Received a call from a local garden center last week regarding downy mildew on a shipment of roses from California that they had hoped to sell for Mother’s Day. Symptoms on the somewhat resistant cultivar Mr. Lincoln could easily be mistaken for a chemical burn. Symptoms on the susceptible cultivar Purple Tiger included obvious lesions on the canes as well as the foliage. Recommended controls measures are to isolate the highly susceptible cultivars from the rest, remove as much of the infected tissue as possible, and begin spraying on a regular basis with fungicides labeled for downy mildew control, such as Aliette, Stature, or a combination of copper and Mancozeb.
Donald M. Ferrin, Ph.D., Louisiana State University Agricultural Center, Baton Rouge, LA