CHARLESTON – Powdery mildew has been detected on South Carolina watermelons, and Clemson University specialist Anthony “Tony” Keinath warns growers to act now to protect their crops.

Powdery mildew produces yellow spots on the tops of the leaves of watermelon plants and white powdery mildew on the undersides.

Symptoms of powdery mildew include yellow and brown spots on watermelon plant leaves.
Image Credit: Clemson University Public Service and Agriculture

Keinath, a vegetable pathologist at Clemson’s Coastal Research and Education Center, reports the fungal disease was found on watermelons at the center this week (May 28).

“All watermelon crops in South Carolina should be sprayed immediately with a fungicide that is effective against powdery mildew,” Keinath said. “Uncontrolled, powdery mildew can reduce the weight and number of seedless watermelons by 40 percent.”

Powdery mildew usually shows up on watermelon as round, yellow spots on the leaves, Keinath said, adding growers should use a 10x lens to check for powdery mildew on the undersides of leaves. Young plants are less susceptible than older plants, so Keinath advises growers to check flowering plants if possible.

Fungicides Keinath recommends spraying watermelon crops  before powdery mildew symptoms are detected with Procure, Quintec, Vivando, Switch or Luna Experience. After symptoms have been found, he recommends using Vivando rotated with Quintec.

For more information, see Clemson’s Powdery Mildew on Watermelon fact sheet.

Information on fungicide options are available in the Clemson Cooperative Extension Watermelon Spray Guide for 2018 and in the Southeastern U.S. Vegetable Crop Handbook 2018.

Watermelons can be grown in all counties in South Carolina. Commercial production is centered in the Lowcountry and Sandhills regions. The watermelon planting season in South Carolina begins in late March in the Coastal Region.

For more information, see the Watermelons Factsheet produced by the Clemson Cooperative Extension Service’s Home and Garden Information Center.