Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu
Conditions for downy mildew continue to be favorable, so preventative control for cucumber is important at this time. To date we have only observed downy mildew on cucumbers.
Powdery mildew is increasing on squash, cantaloupe and pumpkin, and has been seen on watermelon as well. It is often hard to see the infection on watermelon because the fungus sporulates sparsely on watermelon and the leaf color masks the fungus. Look for chlorotic spots on the upper surface of young, fully expanded leaves, and then inspect the corresponding lower leaf surface with a hand lens to confirm the presence of the fungus. On watermelon, if control is needed, alternate Nova /Bravo or Procure/Bravo with Quintec/Bravo or Pristine/Bravo. Any generic chlorothalonil can be substituted for Bravo.