Downy Mildew in Cucurbits
Purplish dark gray spores of
the downy mildew fungus only develop on lower surfaces of leaves and are easily
distinguished from white spores of the powdery mildew fungus.
Note that downy mildew spots often have an
angular appearance because they do not enlarge beyond major veins. This is most evident on the lower
Yellow spots are on the upper
surface of this leaf opposite where spores have developed on the lower
surface. One section of this leaf has
died because of downy mildew.
Photos Courtesy of M.T. McGrath, Long Island
Horticultural Research and Extension Center, Cornell University