Diseases of melon (
Downy mildew
Downy mildew of melons is caused by Pseudoperonospora cubensis. P. cubensis is a fungal-like organism that causes foliar necrosis and decline, and like other downy mildews, is an obligate parasite infecting only cucurbits. It does not affect the roots. Disease occurs on melons in the late summer and early fall during summer monsoon rains and in the late winter and early spring when there rain and heavy dew. With sufficient moisture in the foliage, disease progresses rapidly. P. cubensis produces spores that are carried by splashing water, wind and rain. Plants of all ages are susceptible.
Early infections cause yellow spots on leaves that coalesce, and the
leaf turns brown. When humidity is very high, especially early in the
morning, a white to light purple growth is visible on the underside
of leaves, which consist of asexual spores. Older leaves are usually
infected first.
In areas where disease has been previously confirmed, it is important
to watch for the initial symptoms and signs of disease so that fungicides
can be applied as soon as possible. Protectant fungicides such as chlorothalonil and mancozeb should be applied in rotation with fungicides of other modes of action such as Gavel, Ranman, Previcur and Tanos. Repeat applications of fungicides may be
necessary if conducive weather conditions persist. Alternating different
chemicals is important to avoid development of resistance.
For more information, see the following web site: http://www.ces.ncsu.edu/depts/pp/cucurbit/disease/Image.html
March 3, 2009