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Downy Mildew on Cucurbits

Downy Mildew (Pseudoperonospora cubensis) has been spotted in Santa Rosa County on Pumpkins, Cucurbita pepo.  Downy Mildew (DM) can be devastating on cucurbits in fall plantings.  The disease occurs in temperate and tropic areas with adequate leaf wetness, usually by the dew, with high or low rainfall.  It affects most cucurbits including cucumber, melon, squash, pumpkins, and watermelons.  Prompt action is required to avoid significant loss.


Early stage of Downy Mildew on Cucurbits

The symptoms to look for with DM occur almost exclusively on the leaves.  Most cucurbits with DM first exhibit slightly chlorotic (bright yellowing) areas on the upper leaf.  The symptoms will first appear on the inner most crown leaves (older leaves) and work their way out to the younger leaves.  The chlorotic spots may eventually begin to become necrotic (dead, brown tissue).  The bottom of the leaf will appear dark grey to deep purple depending on the accumulation of spores.  Click here for more pictures of symptoms to look for. 


The chief control measure are fungicide application, resistant cultivars, and cultural practices.  At this point if you have DM on your farm resistant cultivars for this years planting is to late.  There are a few cultural practices to be put in place to reduce DM.  Larger plant spacing to reduce the density of the canopy, to maximize distance of the innoculum.  Also avoid overhead irrigation because it will increase the length of time that the leaf surface is wet.

For chemical control, refer to 2012-2013 Vegetable Handbook for fungicide recommendations to control DM.  If DM is present in your fields now, call your local extension agent to get recommendations for control as soon as possible.







Permanent link to this article: http://santarosa.ifas.ufl.edu/blog/2012/08/23/downy-mildew-on-cucurbits/