The most obvious symptom of cucumber downy mildew are the yellow spots on the top of cucumber leaves that seem to be contained by the veins. On the bottom of the leaf, in the yellow spot there is often black fuzz. These are the spores of the disease.

If you would like to confirm that the disease you are seeing is cucumber downy mildew, you can take pictures of the top and bottom of the leaves that are affected and send them to your local extension agent or bring a sample by the extension office to have it diagnosed.

The best thing to do for this disease is to spray preventatively or once the plants get the disease, pull them out and bury them so the spores won’t continue to spread.