Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu
The weather continues to be very favorable for downy mildew. It is spreading now to hosts other than cucumber. Cantaloupe, watermelon, winter squash and pumpkin have all been infected in the region. The spots are much smaller on butternut squash and watermelon but still produce the small tuft of fungus growth on the underside of the leaf. All cucurbit growers need to be including a fungicide specific for downy mildew in their spray rotation such as Previcur Flex, Ranman, Presidio, or Tanos at this time. Follow the label directions for plant-back restrictions, mixing partners, such as Bravo and mancozeb, and adjuvants. See the 2009 Commercial Vegetable Productions Recommendations for more information. Check the Cucurbit Downy Mildew ipmPIPE web site as well http://cdm.ipmpipe.org for more information.
Downy mildew on the upper surface of watermelon leaves. Fungal growth on the underside of the leaves is often sparse.