Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland; keverts@umd.edu
Downy mildew on watermelon was confirmed in Wicomico County, MD today. When downy mildew is present, watermelon growers need to modify their spray programs because the materials that are typically used for managing more common diseases are not effective on downy mildew. Growers should add additional materials to their spray program. Do not delay sprays because preventative applications are much more effective than applications made after disease is detected. Sprays should be applied on a 7-day schedule. Remember that materials with different Modes of Action (FRAC groups) should be alternated.
The following products have been effective on cucurbit downy mildew in our area. They should be tank-mixed with a protectant fungicide such as chlorothalonil.
● Ranman (2.10 to 2.75 fl oz. 400SC/A, see label for details, do not apply with copper);
● Presidio at 3.0 to 4.0 fl oz 4SC/A
● Previcur Flex at 1.2 pt 6F/A
Other materials for that are good when used in a tank mix or in alternation are
● Tanos at 8.0 oz 50DF/A
● Gavel at 1.5 to 2.0 lb 75DF/A (Gavel contains mancozeb, which is a protectant, and does not need a tank-mix partner)
● Curzate at 3.2 oz 60DF/A
Alternatively Presidio may be applied through drip irrigation. See label for additional details and application information.
Consult the Commercial Vegetable Production Recommendations for further information on resistance management and available fungicides (in Maryland, Extension Bulletin 236 and in Delaware, Extension Bulletin 137).