from the Southeast Farm Press

Oct 9, 2008 9:57 AM,
By Roy Roberson
Farm Press Editorial Staff

system of sentinel plots, similar in design to the soybean rust defense
system, is providing adequate warning for upper Southeast vegetable
growers to protect their crop from downy mildew.

Va., is one of three sites, along with Virginia Beach and the Eastern
Shore, in the state where sentinel plots are checked for disease
development. The Virginia system is part of a national vegetable
disease detection and management system that runs from Florida to

back to back dry growing seasons in southern Virginia, Extension Area
Vegetable Specialist Janet Spencer says cucurbit crops, and watermelons
in particular, have been susceptible to diseases because of typical
early morning heavy dews from July-September. Combined with typical
high humidity, the environment is right, she notes, for downy mildew to

sentinel plots are critical to provide growers with ample time to spray
their crops to protect them from mildew problems. Even with ample
warning, a limited number of fungicides and diseases that can rapidly
develop new races make it tough for growers to stay ahead of diseases.

the upper Southeast, downy mildew is the worst disease problem faced by
cucurbit growers in the fall, according to Virginia Tech Extension
Vegetable Specialist Steve Rideout.

Virginia Extension specialist explains that downy mildew, caused by the
fungal organism Pseudoperonospora cubensis, is most destructive to
cucumbers and cantaloupes, though all cucurbits are susceptible. In
Virginia, where watermelon production has increased since the tobacco
buyout, the disease can severely restrict production of high quality,
high value melons.

of downy mildew first appear as pale green areas on the upper leaf
surfaces. These change to yellow angular spots. A fine white-to-grayish
downy growth soon appears on the lower leaf surface.

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