Melon Disease Forecaster 2024 – Vegetable Crops Hotline

Melon Disease Forecaster 2024



This article was originally written by Dan Egel, who retired from Purdue. Please contact the PPDL for more information.

MELCAST is a weather-based disease-forecasting program that helps growers schedule foliar fungicide applications for cantaloupe and watermelon. MELCAST stands for MELon disease for CASTer. This program, designed by Dr. Rick Latin, Professor Emeritus of Plant Pathology at Purdue University, keeps track of weather conditions so that cantaloupe and watermelon growers can apply foliar fungicides to their crops when they are most needed. MELCAST was designed for foliar diseases: Alternaria leaf blight, anthracnose, and gummy stem blight. In a typical year, MELCAST will save growers 2 to 3 foliar applications of fungicides without sacrificing yield. MELCAST works by having growers apply fungicides at specific Environmental Favorability Index (EFI) values instead of using a calendar-based schedule. The extension bulletin “Foliar Disease Control using MELCAST” BP-67 describes this program in more detail.

To use MELCAST, follow these steps:

Apply your first foliar fungicide application when vines first touch within a row or earlier.

  1. Find a MELCAST site near your farm. A table with the 2023 MELCAST locations can be found at info, or to receive a hard copy of the MELCAST Update, see below. Select a MELCAST site near enough to your farm that the weather is similar to your field.
  2. Go to info, and click on the MELCAST location near you. A table listing the EFI values over the past 7-days will appear. I like to click on the state summary below the table to read MELCAST values. Information at each location at includes EFI’s for cantaloupe and watermelon for the past 7 days, total precipitation, high temperature, and growing degree days.
  3. Write down the EFI value on the date when the first fungicide was applied on your MELCAST Record Sheet (contact me for a hard copy). Note that the EFI values are cumulative. That is, the values keep increasing.
  4. It is not necessary to read the MELCAST EFI values every day. Keep in mind, however, that cantaloupe growers will apply a foliar fungicide again at 20 EFI values and watermelon growers will use a 35 EFI threshold. So, when the EFI values are close to the threshold, read the MELCAST EFI values each day.
  5. When a fungicide has been applied, write down the new EFI value for the date the spray was made. If at all possible, do not let the EFI values go over the threshold. It is better to apply a fungicide before the threshold is reached than to wait until the threshold has gone over.
  6. If 14 days have expired and the threshold has not been reached, apply a foliar fungicide anyway. This is because after 14 days, new growth will have occurred, and some of the products applied 14 days ago will have weathered. Again, when the next fungicide application has been made, note the EFI value.

Using MELCAST is much like keeping track of the mileage for oil changes in your truck. Note the accumulated EFI values when you make your first spray, much as you would write down the mileage on your truck when you change the oil. Make your next spray when the EFI threshold nears the threshold by keeping track of the accumulating EFI values much as you would change the oil in your truck every 4,000 miles (for example).

Starting in mid-May, a weather and disease information summary will appear weekly on the state summary page and in the mailed copy of the MELCAST Update.

By contacting Barb Joyner at, you can sign up for a free hard copy of the weekly MELCAST Update newsletter (during the season).

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