CHARLESTON — Some fungicides used to control powdery mildew on squash will significantly improve yields on seedless watermelon too, according to recently published research by Clemson University Extension specialist Anthony Keinath.

The research helps growers establish cost-effective fungicide treatment plans that reduce loss to disease.

A watermelon sits in a field.

A watermelon sits in a field.

Keinath conducted a two-year research project at Clemson’s Coastal Research and Education Center in Charleston to evaluate fungicides’ effectiveness in controlling powdery mildew on watermelons. The project showed that using certain fungicides increased the marketable weight of seedless watermelon by 75 percent over fruits that were not sprayed.

The findings of Keinath’s project were just published in the scientific journal Crop Protection and are available online here.

“Because the powdery mildew fungus develops a resistance to fungicides after a couple years of application, it was time to evaluate which ones of the older fungicides were still working and how the newer fungicides compared to them,” Keinath said.

As part of the project, Keinath also sought to see if fungicides for gummy stem blight would also control powdery mildew. Applying just one fungicide instead of two could lower input costs for growers.

“But the short answer is ‘No, fungicides for gummy stem blight will not control powdery mildew,’ so growers need to add other fungicides to their spray program for powdery mildew,” Keinath said.

The results of this study are incorporated into the fungicide application recommendations made in the Watermelon Spray Guide for 2015 released by Keinath and Extension Horticulturist Gilbert Miller. The guide provides step-by-step instructions on which fungicides to apply and when.

South Carolina growers harvest around 7,300 acres of watermelons each year valued around $27.6 million, according to the National Agricultural Statistics Service.

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