Many cantaloupe and watermelon growers have planted transplants in the field or will soon. A question many growers often have is when and how should one apply fungicides. Applying fungicides according to a weather-based system is easy for cantaloupe and watermelon growers. MELCAST was developed at Purdue University by Rick Latin to allow growers to apply foliar fungicides to control Alternaria leaf blight, anthracnose and gummy stem blight. When MELCAST is followed, fungicides are applied when they are most needed depending on leaf moisture and temperature. Details are listed below or in the extension bulletin, Foliar Disease Control Using MELCAST, BP-67-W. Download the bulletin at www.extension.purdue.edu/extmedia/BP/BP-67-W.pdf or contact Dan Egel for a copy.
The MELCAST program uses weather information from one of the 12 sites located around Indiana: Daviess County, Decker, Elkhart County, Gibson County, Jackson County, Oaktown, Richmond, Rockville, Sullivan, SW Purdue Ag Center, Vincennes, and Wanatah. MELCAST also serves growers in Kentucky, Michigan and Missouri. Cantaloupe and watermelon growers should farm within about 50 miles of a MELCAST site. If rain events, dew formation, and temperatures at one of the MELCAST sites are similar to your farm, MELCAST should be effective for you. Cantaloupe and watermelon growers using MELCAST apply foliar fungicides every 14 days unless the weather thresholds described below indicate that an application should be made sooner. A step-by-step list of how to use MELCAST can be found below.
- Apply initial fungicide application at or before vines touch within a row.
- Check the Environmental Favorability (EFI) value for the day of fungicide application.
- Calculate the threshold for the next application by adding 20 (cantaloupe) or 35 (watermelon) to the EFI value in step 2. It is important for cantaloupe and watermelon growers to use the EFI values designed for their crop. To get a MELCAST calendar to keep track of EFI values, call Dan Egel. Alternatively, a MELCAST spreadsheet can be downloaded from melcast.info.
- Apply the next fungicide application 14 days after the first, or sooner if the EFI threshold has been reached.
- Check the EFI values on the day you make your next fungicide application and re-calculate the threshold for the next application.
A few things to remember: It is best to apply fungicides before the threshold has been reached then after. So, for example, if you are a watermelon grower, the EFI threshold has reached 33 and a rain is expected soon, then go ahead and apply a fungicide. Use the thresholds of 20 and 35 EFI values as guides. Use a lower threshold if you feel that disease pressure is high. Finally, note that fungicide applications for downy mildew and powdery mildew cannot be scheduled with MELCAST.
Keeping track of MELCAST values is similar to keeping track of oil changes in a car or truck. When one changes oil, the mileage is written down and the oil changed at the next threshold (3,000 miles or 35 EFI values). EFI values, like mileage of a truck, continue to increase. Check EFI values by using the toll-free phone number (800) 939-1604 Monday though Friday; check the website 7 days a week btny.agriculture.purdue.edu/melcast/ (or remember melcast.info); or sign up for the free MELCAST Update that comes once a week during the season. Please call Dan Egel with any questions.