Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland; keverts@umd.edu
The weather based forecasting program MELCAST on watermelon began on Wednesday (May 25). MELCAST is a weather-based spray scheduling program for anthracnose and gummy stem blight of watermelon. If you received a report in 2010, you should have automatically received the first report. If your email or Fax number has changed, please call us. If you did not receive a report and would like to, please call Jeri Cook at (410) 742-8788 and give us your name and Fax number or e-mail address. MELCAST also is available online – bookmark the site http://mdvegdisease.umd.edu/. Click on the watermelon picture.
To use MELCAST for watermelons, determine which site is closest to your farm field. Apply the first fungicide spray when your watermelon vines meet within the row. Additional sprays should be applied using MELCAST. Accumulate EFI (environmental favorability index) values beginning the day after your first fungicide spray. Apply a fungicide spray when 30 EFI values have accumulated by the weather station nearest your fields. Add 2 points for each overhead irrigation that is applied. After a fungicide is applied, reset your counter to 0 and start over. If a spray has not been applied in 14 days, apply a fungicide, reset the counter to 0 and start over. Please call if you have any questions on how to use MELCAST on your watermelon crop (Kate Everts at 410-742-8789).
Because there is widespread resistance to strobiluron (group 11) fungicides in Maryland and Delaware, growers should alternate one of the following with chlorothalonil (Bravo, etc.); a tebuconazole product (such as Folicur), Inspire Super, or Switch. Resistance to Pristine has been recorded in many watermelon fields in the southern U.S. We have not found resistance to Pristine here in Delaware or Maryland, yet. However, Pristine should be used with great caution; always tank mixed with chlorothalonil; and alternated with a fungicide that has a different mode-of-action. If a serious disease outbreak occurs in your field, return to a weekly spray schedule.