Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland; keverts@umd.edu
Until this past week, the only cucurbit crop with downy mildew in the area was cucumber. However this past week I have confirmed downy mildew on watermelon, cantaloupe, butternut squash, and giant pumpkin, including hubbard squash. This means that all cucurbits should be protected with a targeted fungicide spray. For specific details see http://extension.udel.edu/ag/vegetable-fruit-resources/commercial-vegetable-production-recommendations/. We have good products available for this disease. Organic growers are strongly advised to use copper applications to slow the spread of this disease in their production fields.
In addition, keep good powdery mildew materials in your spray program. Powdery mildew has also moved into the area.
Management of downy mildew should use the following products tested in our area. Select two that are in different FRAC code groups, and alternate them. Tank-mix with a protectant such as chlorothalonil or Gavel.
|
Product |
Efficacy on Downy Mildew |
| Presidio (43) | excellent |
| Ranman (21) | excellent |
| Zampro | excellent |
| Revus (40) | good in alternation or tank mix |
| Previcur Flex (28) | ? (the pathogen may be developing resistance) |
| Tanos (11 + 27) | good in alternation or tank mix |
| Curzate (27) | good in alternation or tank mix |
Figures A and B. Downy mildew lesions on pumpkin are initially seen on the upper surface as angular water soaked or yellow spots (A) that are limited by the leaf veins. The angular nature of the lesions is especially evident on the lower leaf surface where sporulation occurs (B). Look for grey angular lesions on the under surface of leaves after dewy nights. Lesions will expand and become necrotic over time.