CLEMSON — Pending rains will put watermelons at risk for gummy stem blight and anthracnose, said Tony Keinath, Extension specialist and vegetable pathologist at the Clemson University Coastal Research and Education Center in Charleston.

Keinath and Extension Horticulturist Gilbert Miller this week released the Watermelon Spray Guide for 2015, which provides step-by-step instructions for applying fungicides to target such diseases as anthracnose, powdery mildew, fruit blotch and others. The guide includes details on when to spray in the event of rain, as well as which fungicides to group together, among other tips. Download the spray guide here.

A watermelon sits in a field.

A watermelon sits in a field at the Coastal Research and Education Center in Charleston.

The guide was updated following field trials in 2013 and 2014 that helped rate the best fungicides for anthracnose, powdery mildew and downy mildew.

In the past two years, anthracnose has become more common as growers concentrated fungicide applications to combat gummy stem blight, Keinath said. Anthracnose causes spots and blisters on fruit, as well as leaf spots and one inch spots on vines.

“I have noticed less pressure from gummy stem blight in the last couple years. It is not the one top disease any more,” Keinath said. “I hope growers are getting back to a fungicide schedule that addresses anthracnose, too.”

Keinath and Miller added information to this year’s spray guide on the fungicide Quadris Top, which is effective against both anthracnose and gummy stem blight.

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

Growers began transplanting in early March and are likely applying the first fungicide spray of the season now. Growers should first spray about three weeks after transplanting, then every 10 to 14 days during dry weather or about twice as frequently in wet conditions.

Typically, watermelon disease begins to rear its head in late April or early May. The Lowcountry concluded its driest week of the year on April 10, but rains are expected the coming week.

“That will put the early-season crop at risk for gummy stem blight and anthracnose,” Keinath said.