Downy Mildew In N.C.

Downy Mildew has been identified on a field of cucumbers in Franklin County, North Carolina. Downy mildew, caused by the fungus Pseudoperonospora cubensis, is found annually on squash, cucumbers, pumpkins, and muskmelons grown in all areas. Symptoms of disease on cucurbits, other than watermelon, show up as small yellowish areas on the upper leaf surface. Later, a more brilliant yellow coloration occurs with the internal part of the lesion turning brown.

Usually the spots will be angular as they are somewhat restricted by the small leaf veins. When the leaves are wet, a downy white-gray-light blue fungus growth can be seen on the underside of individual spots (lesions). On watermelons, yellow leaf spots may be angular or non-angular, and they will later turn brown to black in color. Often on watermelons, an exaggerated upward leaf curling will occur.

Downy mildew is a very destructive disease and progresses rapidly under favorable conditions. Fungicides are much more effective when applied well before symptoms are visible. Initiating a downy mildew control program after symptoms have been detected is much more likely to fail. For further information on control and how to track the movement of downy mildew throughout North Carolina go to the following website. http://www.ces.ncsu.edu/depts/pp/cucurbit/