Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland; keverts@umd.edu
July 2, 2015 – The UD Plant Diagnostic Clinic confirmed downy mildew on watermelon July 1. This is very early for us to see downy mildew in Maryland or Delaware. Downy mildew can advance rapidly on watermelon and cause extensive yield losses. Fields should be protected with fungicide programs that include products that have specific efficacy on downy mildew. Products that work well on downy mildew include Zampro, Ranman and Gavel. Other materials that will contribute to diseases control can be used in rotation as tank mix partners with a protectant: Ariston (Contains chlorothalonil and the active ingredient in Curzate), Forum, Tanos, Curzate, or Presidio.
Organic growers have fewer choices, but can use copper and Serenade or Sonata to slow down the epidemic. Preventative applications are more effective than applications made after downy mildew is detected.
Symptoms of downy mildew on watermelon.