CLEMSON — Last week’s cold snap may be a setback for the state’s watermelon season. Clemson University plant disease specialist Tony Keinath points out that a repeat performance of last year’s spring could create problems.

Last week's cool weather may delay this year's South Carolina watermelon crop.

Last week’s cool weather may delay this year’s South Carolina watermelon crop.

“Because of the wet, cool spring, there will be more disease problems on young plants than normal, similar to what we saw last year,” said Keinath, a researcher and Extension Service specialist at the Coastal Research and Education Center in Charleston.

Keinath remembers last year well. “The cool spring slowed watermelon growth after transplanting,” he said. “My watermelons did not grow at all the first three weeks after transplanting, which delayed harvest by one to two weeks.”

Because of the late start to the growing season, the first South Carolina watermelons likely will be harvested in mid-June. In some years part of the crop has been ready in early June.

A delay can be a headache for growers, but if the weather spawns more disease problems, that can put a dent in the $30 million-plus crop. Diseases mean losses and higher costs to control them.

Fungus is the biggest problem. Fungi cause five serious plant diseases.

“Fusarium wilt, gummy stem blight and anthracnose are the most severe, followed by powdery mildew and, in some fall crops, downy mildew,” said Keinath.

Keinath and Gilbert Miller, the watermelon Extension specialist at the Edisto Research and Education Center in Blackville, coauthor a watermelon spray guide for commercial growers. Fungicide recommendations for anthracnose, powdery mildew and downy mildew were updated for 2014.

Keinath has been working with watermelons for 23 years: “Every year since I came to Clemson in 1991,” he said.

More than two decades of working the watermelon patch has given Keinath some insights. When it comes to selecting varieties to grow, “I still like the flavor of Charleston Grey watermelon. Crimson Sweet has a little more disease resistance than Charleston Grey,” he said.

Watermelons grow best with full sun in well-drained soil, such as sandy loam, making the Carolina coastal plain an ideal region for commercial watermelon growing.

For professionals and amateurs alike, Keinath recommends that “early crops should be set out as transplants to give them a head start in cool soil. Because it is difficult to weed around the vines, the ground should be covered with mulch to block weeds and to conserve moisture when the weather turns hot. Watermelons should be sprayed with fungicide at least every other week, starting when the first flowers appear and continuing until the first fruit are ripe.”

Ripeness raises another issue: how to select a sweet, ready to eat melon? Keinath offers these tips.

“Look for fruit with a slightly wavy or uneven surface and, most importantly, the belly of the fruit should be a creamy yellow color,” he said. “To pick a fruit that is sweet, the fruit should be heavier than other fruit that are the same size. To pick a ripe melon from the plant, the tendril closest to the stem of the fruit should be dried or dead.”

For more help with watermelons, commercial growers should contact their county Extension agents or Keinath or Miller. Home gardeners should check the Home and Garden Information Center or a contact a Master Gardener in their county Extension office.