BLACKVILLE — Planting watermelons later in the season can limit the presence of Fusarium wilt, new research at Clemson University shows.

“Fusarium wilt is the main cause of watermelon collapse, wilt and dieback,” said Clemson Extension plant pathologist Tony Keinath, speaking at the annual Watermelon Field Day at the university’s Edisto Research and Education Center in Bamberg County.

Adjusting transplant dates is just one method Clemson specialists are studying to combat the disease that attacks plant roots and stems and has become an increasing problem for watermelon growers. Grafting watermelon with squash and other disease-resistance plants also shows promise in combatting Fusarium wilt.

Charts shows the presence of Fusarium wilt declining as watermelons are planted later in the season as soil temperatures increase.

Charts shows the presence of Fusarium wilt declining as watermelons are planted later in the season as soil temperatures increase.

Fusarium wilt persists in cool, wet soil. As the soil temperature tops 81 degrees, the disease becomes less common, Keinath said, citing two years of research he conducted at Clemson’s Coastal Research and Education Center in Charleston. Watermelons planted in mid-March 2015 suffered Fusarium wilt damage 80 percent of the time, compared to just more than 10 percent of watermelons planted in late April, he said. While research results are preliminary, Keinath said he is confident planting later will reduce Fusarium wilt.

Additionally, despite planting a month later in the growing season, watermelon yields were largely unchanged.

“It is encouraging to see that we’re not reducing yield when planting later in the season,” Keinath said.

The question, he said, is whether growers would miss peak market demand at July 4 by planting later.

“The watermelon market is not over in mid-July like it used to be,” Keinath said.

Marketers are identifying new uses to extend demand for watermelon beyond the summer. Rob Paladino, the chief executive at WTRMLN WTR, told field day attendees his company is buying watermelons from South Carolina and other states to produce cold-pressed watermelon juice. WTRMLN WTR is sourcing 25 million pounds of watermelon in 2016 with plans to grow.

Clemson University horticultural specialist Gilbert Miller organizes the annual Watermelon Field Day to share research that can help growers maximize yields and profits.

Clemson University horticultural specialist Gilbert Miller organizes the annual Watermelon Field Day to share research that can help growers maximize yields and profits.
Image Credit: Clemson University

Keinath’s colleagues Richard Hassell, Clemson Extension vegetable specialist, meanwhile, and Clemson horticulturalist Gilbert Miller are testing grafted watermelon in which the fruit-producing tops of plants are fused to the roots of squash to make the sweet summer staple more resistant to Fusarium wilt and other soil-borne diseases. Hassell is working with the U.S. Department of Agriculture to develop new rootstocks with resistance to Fusarium wilt as well as root-knot nematodes. He also is working to reduce labor costs with the use of a robotic grafting machine that makes precise cuts and grafts.

“Grafting is an art and a science,” Hassell said. “Robots take out the art.”

More than 200 people attended the Watermelon Field Day organized by Miller, who treated attendees with a tasting of more than 99 varieties planted at the Edisto research station.

In addition to hearing presentations from Miller, Hassell, Keinath and Paladino, attendees learned about Clemson research on the use of wildflowers to attract native bees, wasps and other pollinators, among other presentations.

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