Two Newly Identified Viruses In Florida Could Impact Watermelon Growers – The Ledger

LALELAND – Two new viruses had been circulating among watermelon fields since 2019, and it took a lot of footwork by university plant pathologists to identify them.

They identified the WaCLAV-1 and WaCLAV-2 viruses last week; the letters are an abbreviation for Watermelon Crinkle Leaf Associated Virus.

According to Pamela Roberts, a plant pathology professor with the University of Florida IFAS Extension, the viruses are new because known virus tests could not detect them and determine the cause of the damage to the watermelon crops. A tip from Texas, where the viruses appeared this spring, led her to test for the new viruses here.

Both new viruses were found last week in watermelon plant leaves collected from a commercial farm in Florida.

“This just gives us an explanation for what growers have seen before,” Roberts explained. The new virus-infected plants display symptoms that are similar to other known viruses, which make the identification more difficult.  

Watermelon broker and grower Lee Wroten said he has seen viruses affect watermelons before in the early 2000s. and based on observations and talking to other farmers in recent years, he had suspected that something was happening to the crop.   

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“We sort of knew we had something going on, but we just didn’t know what it was.” Wroten said after hearing about the new virus. “I am really glad they have identified it.” 

Wroten is with Lakeland-based Global Produce Sales, Inc., which has an 800-acre watermelon farm, Moore Haven Melons LLC in South Florida and a 600-acre farm in South Georgia, and also works with contracted farmers in Polk County and other states throughout the watermelon growing season. The company also has a packing plant, Triploid Packing LLC. 

He said watermelon growers invest between $3,000 to $4,000 per acre to plant the crop. He explained that the watermelon virus attacks plants, not people, but the impact on the watermelons could eventually mean a rise in production costs for growers, and that could increase the price of watermelons. 

Wroten said earlier viruses in the early 2000s nearly made it too financially risky to plant watermelons in Florida. Infected crops were too bitter in taste and inside they had the texture of jelly.  

In the past, researchers first identified the virus and then determined how it was transmitted. He said the white fly was the culprit. He and other growers had to spray to reduce the tiny insect population and produce marketable watermelons.

Wroten is a third-generation grower whose family started in the citrus industry, he said, noting watermelons were a summer crop planted after the citrus harvest to generate additional revenue.

He has been working with researchers as part of his roles with state and national watermelon industry groups, including the National Watermelon Association. Wroten said the best natural treatment for viruses transmitted by the white fly is a long chilly winter to kill the pests.  

Florida is the only U.S. supplier of watermelons from December to April. Florida watermelons are harvested throughout the year, although the vast majority of production is harvested from May to July. Production costs can be higher in South Florida than in North Florida. But South Florida growers can enter the market early, providing them with prices up to two to three times higher than those received in North Florida. 

According Roberts, Polk County does produce limited amounts of watermelons, and growers have provided researchers with samples for diagnostics in the past, but not necessarily related to a virus. Acreage for the Polk crop is smaller than in other counties.  

Florida watermelon growers overall are some of the most productive in the nation because of the state’s different climate zones, which extend the growing season. From 2017-2020, Florida was the No. 1 state in watermelon production, according to the U.S. Department of Agriculture National Agricultural Statistics Service. In 2020, Florida produced more than 850 million pounds of watermelon.  

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“Now that it is known that there are additional (watermelon) viruses in the mix, efforts can be made to determine their impacts and how to manage them,” Roberts said in a blog post announcing the new viruses. “The viruses very likely occur in mixed infections, with the other viruses already present in Florida and other watermelon-producing states.” 

Roberts, a faculty member at the Southwest Florida Research and Education Center, wrote in a paper last week that she and her research colleagues found watermelon crinkle leaf-associated virus 1 and 2 in Charlotte, DeSoto, Glades, Osceola and Seminole counties. 

“There is always concern when there is a new pathogen detected and the potential implications it can have on the crop,” Roberts said. “Unfortunately, so little is known about these viruses that we cannot predict anything about them.”

“We do have evidence that it has been in watermelon for the last two seasons, and we found it because it looked like other virus symptoms,” she said.

Roberts first learned of the potential of the new virus coming to Florida after hearing a report about it from Texas. She started talking to a plant pathologist at Texas A&M University, and he sent photos. That’s when she decided to test watermelons in Florida for the virus, which has also been detected in China and in Brazil.  

Until more information is available regarding these viruses — including how they are spread — university researchers recommend growers continue using their current programs to control insects in their crops. 

Growers who suspect they might have watermelon crinkle leaf-associate virus 1 and 2 can bring leaf samples to the plant diagnostic lab at the Southwest Florida REC and to the lab at the North Florida Research and Education Center in Quincy.

Meanwhile, Roberts will be out in the watermelon fields again this fall looking for insects to determine how these new viruses are spreading.

For Wroten, the new viruses are like a flashback. 

“Here we go again,” he said of the difficulty farmers experience. “One more challenge to add to our list.”