Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland; keverts@umd.edu
The cucurbit crops that are the most susceptible to powdery include pumpkin, squash, muskmelon, and cucumber that does not have resistance. However, in the past ten years, I have seen more and more watermelon fields where powdery mildew has become a problem. Quintec, a new fungicide that has excellent activity on powdery mildew, is registered on melons.
Remember that resistance to group 11 fungicides (strobilurin fungicides such as Quadris, Cabrio, or Flint) is widespread around the U.S. – do not rely on these materials. A good program for watermelon or muskmelon (cantaloupe) is to scout for powdery mildew and if it is present in the field, apply chlorothalonil plus Quintec rotated with Nova or Procure plus chlorothalonil. Quintec, a group 13 fungicide, has performed well in trials. Quintec has a 3 day PHI and is applied at 4 to 6 fl oz/A in 30 gallons of water (optimum spray volume). Aerial application is not allowed.