Downy Mildew Leaf Symptoms and Signs

Disease identification in wine grapes can be confusing, even for the “experts,” so it is good to continually reinforce your knowledge of diseases and their symptoms (spots or discoloration on a leaf for example) and signs (actual pathogen fruiting structures and other tissues you can see with the naked eye or a hand lens) — especially important for early disease identification.  Most folks do not have a microscope available, but a good hand lens and basic visual assessments can help in identifying diseases.  The more times you observe a disease and its symptoms/signs, the easier it is for you to get it right the next time.  Relative leaf and fruit diseases, distinction of downy mildew and powdery mildew are critical, as many of the downy mildew fungicides have no activity on powdery mildew, and vice versa.  If you falsely identify downy mildew as powdery mildew, you are likely to start an aggressive spray program for powdery mildew that just allows the downy mildew to only get worse.  The short video clip below should help you to identify downy mildew on leaves.  I hope it is helpful to you as you are looking for diseases this week and for the future.  I would encourage you to keep a hand lens on your person whenever you are going through the vineyard, but at a minimum, have one in your office to help in diagnosing diseases and scouting for mites and insects.  Happy hunting!