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During our recent Melon Scouting School, a grower asked me about the disease control philosophy that the plant pathologist seemed to be giving. This grower perceived that there was a difference between the way this pathologist approached preventive spraying, in contrast to the pathologist who spoke at last year's Watermelon Grower's Meeting. "Which one is right," the grower asked?

While I don't doubt that there are some minor differences between the disease control philosophies between the two pathologists, I think there is more common ground than might come across. I've talked to both of these researchers in depth on several occasions, and believe that there is a lot of common ground.

So I have taken a basic set of guidelines, gleaned from both pathologists, and have run these ideas by both of them for comments. The points that follow summarize both of their positions.

1. Both pathologists would encourage growers to start a preventive spray program early in the season. You know, without doubt, that certain fungal diseases will be in the area, and will need to be addressed. Don't wait till you have them to start spraying. You need to be spraying before diseases start, since most fungicides do not eradicate diseases once they are established. They usually only slow down the spread of diseases. Spray for what you expect will normally show up in a typical growing season.

2. Be sure to rotate fungicides between spraying. Both pathologists have told me that they are concerned about disease organisms that develop fungicide resistance. By rotating between different classes of fungicides, this will help delay the day that resistant organisms develop.

3. Spray less expensive fungicides early, and save the more expensive "big guns" for later in the season when you really need them. Some less expensive fungicides do a good job of controlling disease, and these are good to use at the start the season. And generally, they are good to use later on as well, in rotation with the more expensive fungicides.

4. Spray for what you know is there. Later in the season, as diseases start to show up, you will want to adjust your fungicide program to address the particular diseases that you see. Some fungicides are targeted toward specific diseases, and you will want to include them in your spray program. The "general purpose" fungicides that you start the season out with cover a wide range of diseases, such as anthracnose and gummy stem blight. They often give some control over downy mildew. But if downy is found in the area, you will probably want to include fungicides which "specialize" in controlling downy mildew. That is true for powdery mildew as well.

5. Spray on a regular schedule, but watch out for rain. It's best to maintain a regular spray schedule, but if rain is in the forecast, don't be afraid to spray a day or two before you would normally spray, so that you get the fungicide on well before the rain falls. If you don't have your fungicide on before the rain starts, and if it stays rainy for a while, you could lose your crop. You may also need to spray more frequently during times when weather conditions are favorable to diseases.

6. Avoid spraying fungicides in the heat of the day, if possible. Occasionally you may see plant injury after applying fungicides. This may be avoidable if you choose to avoid spraying during the hottest time of the day.

The melon season is progressing pretty much on schedule. Those growers who grow transplants have had them in the greenhouse for several weeks. In about a month, we'll see those transplants going in the ground.

And as always, please don't hesitate to contact me if you have any questions or problems that develop in your melon field.


		Sarah Denkler, Horticulture Educator University of Missouri Extension P.O. Box 160, Kennett, MO 63857 573-888-4722 Denklers@missouri.edu Updated 04/18/08

Southeast Region