Each new season brings a new set of challenges/opportunities. Watermelon producers will face some fungicide shortages and some newly labeled products to consider. The diseases of concern will soon show their hand and require grower decisions.

Much of the details of this article are from Clemson Extension Publication IL 86 written by Dr. Tony Keinath and Gilbert Miller. They begin the fact sheet with simple recommendations: start early; rotate products based on diseases present; and schedule sprays based on the weather. Sounds easy enough.

In order to be effective at any fungicide program, knowing what diseases to look for is the first step. Gummy stem blight, anthracnose, alternaria leaf spot, powdery mildew and downy mildew are the most common foliar diseases in N.C. Of these, gummy stem blight (GSB) is the main one to deal with year in and year out. GSB usually begins on the older leaves and on the leaf margins. Anthracnose is more angular and much darker than GSB and it can infect the fruit. Alternaria can look very similar to GSB. Powdery mildew is a dry weather disease in melons, which shows white powdery spots on the top or bottom of leaves. Downy mildew can favor anthracnose at first glance, but a closer look will reveal the dark mildew on the lower side of the leaf. The symptoms described here are seen first when scouting the field. These diseases can usually be confirmed in the field by looking for the disease structures under a hand lens.

Keinath refers to the first spray of the season as the most important. This spray may be the only chance to prevent a problem. It is much easier to stay healthy than to get well. It will be applied (hopefully) before disease starts and therefore should be a protectant fungicide. Specific products will be discussed later. The first spray should go on when the vines begin to run and before the vines begin to canopy.

Rotating products is critical for a couple of reasons: to choose the correct product for the disease and resistance management. As the old saying goes, “you don’t want to bring a knife to a gun fight,” so it is with fungicides. Some fungicides, such as Bravo and Dithane, are broad spectrum and can be effective on many diseases while others, like Procure, only target powdery mildew. Bravo, Dithane, Pristine, Cabrio, Quadris, Folicur and Switch are the better GSB control options. Pristine has been very good at controlling GSB in N.C. However, resistance has occurred with the strobilurins (Pristine, Cabrio, and Quadris) in other parts of the country so it is important to incorporate the newer fungicides into a successful program to try and maintain the success. Products in different fungicide groups should be alternated for optimal resistance management. A fungicides group can easily be found in bold on the label of newer containers and also in the Agricultural Chemical Manual. One last comment on specific fungicides, it appears that Pristine will be in short supply for 2009.

The third component of the recommendations is spray schedule. In earlier spring crops grown under moderate to dry conditions, spray every 10-14 days. In wet periods, the scheduled should be shortened to 5 to 7 days. The later into the year watermelons are grown, the shorter the spray interval should be.

This article has compacted the spray recommendations for watermelon to three basic steps: start early; rotate products; and proper scheduling. Obviously, it is a little more involved than that but if you as a grower master follow those steps, you are well on your way to a successful fungicide program.

For more information, please contact the N.C. Cooperative Extension Office at 592-7161.