During the 2022 Clemson University Watermelon Field Day, growers learned overuse of tebuconazole has resulted in resistance in watermelons and other cucurbits leaving growers to rely on more expensive alternatives to treat their crops.
Tebuconazole is an ingredient found in several fungicide products and is used to treat fungal and disease problems such as gummy stem blight, leaf spots and anthracnose. It was first used in 2008 and has been applied frequently to watermelon and other cucurbit crops since that time. Now, gummy stem blight is beginning to show resistance to tebuconazole.
Clemson Research and Cooperative Extension Service vegetable pathologist Tony Keinath said he “…knew this day was coming,” adding watermelon production is about to get a little more expensive.
“One reason we’re where we are today is because tebuconazole is less expensive to use and we’ve used it a lot on our watermelons,” said Keinath, who is located at Clemson’s Coastal Research and Education Center (REC). “Watermelon and other cucurbit growers should reduce the use of tebuconazole to manage gummy stem blight as the fungus has become moderately resistant to this very commonly used fungicide.”
Symptoms of gummy stem blight are large, round spots on the edges of leaves and dry cankers on main stems. Tebuconazole-resistance has been found in South Carolina and Georgia watermelon crops. Alternatives include applying mancozeb and chlorothalonil early in the season and Inspire Super and Miravis Prime later in the season. For more information, read the Clemson 2022 Watermelon Fungicide Guide.
Disease and weed control
In addition to gummy stem blight, diseases and weeds also present problems for watermelon growers. Matthew Cutulle, Clemson weed scientist also located at the Coastal REC, addressed using anaerobic soil disinfestation (ASD) to manage soilborne diseases. This strategy was first developed in Japan in 2000 as an alternative management strategy to soil fumigation and involves applying organic matter (carbon source) to soil, followed by irrigation, to create an environment toxic to diseases, nematodes, weeds and insect pests.
Despite its positive effects on agriculture, ASD is not widely used, mainly because of high carbon-source costs. Cutulle is leading a study of researchers who plan to develop methods to identify agricultural carbon waste streams for promoting the use of ASD.
In addition to high carbon costs, using ASD in watermelon presents other challenges including maintaining proper soil health. Bhupinder Farmaha, Clemson Extension nutrient management specialist at the Edisto REC, is studying how carbon sources affect soil health to determine sustainable practices for using ASD in watermelon.
Angela Rainwater from Growers for Grace is working with the researchers to determine what carbon sources are best to use for anaerobic soil disinfestation. Chicken litter and molasses, and cotton seed meal are carbon sources used in the study. Finding new carbon sources could help growers adjust to supply chain issues and provide them with the carbon they need, she said.
“We’re trying to determine what makes a good carbon source,” Rainwater said. “To do this, we’re going back to the basics and finding what is one grower’s waste is another grower’s input.”
As for weeds, Cutulle said nutsedge is a “driver weed” in watermelon. Several control measures can be used for this weed including herbicides, permanent seedbed technique, solarization, polyethylene mulch system and cover crops. To find out more about Cutulle’s research, visit the Clemson College of Agriculture, Forestry and Life Sciences webpage Weed ID and Biology, https://bit.ly/WeedID_and_Biology.
Proper pollination is another important tool for successful watermelon production. Ben Powell, Clemson Extension Apiculture and Pollinator Program coordinator at the Pee Dee REC, said using suitable pollinators is important for cucurbits. Honey bees are not the best pollinators for watermelon.
“Honey bees are used to pollinate watermelons and other cucurbits, but they are not highly attracted to watermelon flowers,” Powell said. “To get honey bees to pollinate watermelons, growers need to control competing flowers in the field and wait to introduce the hives when the watermelon plants are actively blooming.”
Protecting pollinators is important and easy. Activities people can do to ensure pollinators are protected include planting native flowering plants to attract and benefit local pollinators, reducing mowing and allowing flowering groundcover to remain as forage for pollinators and limiting herbicide use.
For more information on pollinators and pollination contracts, growers can visit the South Carolina Beekeepers website: https://scstatebeekeepers.com/, or the United States Department of Agriculture’s website: https://www.usda.gov/pollinators.
Clemson Extension weather network
Weather knowledge is something else that can benefit growers and the lack of weather data available to South Carolina growers led to the creation of a statewide weather monitoring network. Chris Thomas, Clemson Extension state weather station technician located at the Sandhill REC, talked about the weather system.
“Clemson Extension agents and specialists realized the need for a weather monitoring network and a proposal was made to establish a statewide weather station infrastructure,” Thomas said. “The project’s goal was to establish a weather station in every county to help provide real-time and historical weather data. A total of 50 stations have been installed with at least one in each of the state’s 46 counties.”
The project’s next step is to create a website to house the data. Once this website is built, calculators will be developed to help growers and agents make better recommendations based on actual weather data. These calculators will include weather data on rainfall, growing degrees and chill hours. Clemson University will work with strategic partners such as the SC Department of Natural Resources Climatology Office, USDA Natural Resources Conservation Service and the South Carolina Farm Bureau to collect and utilize statewide weather data to make better predictions and recommendations.
“This will help us forecast possible disease and/or pest outbreaks,” Thomas said. “South Carolina residents will benefit if we can predict these weather-related outbreaks.”
Gilbert Miller, Clemson Extension vegetable specialist and field day coordinator, said the ability to predict weather will be beneficial for South Carolina growers.
“The way I see this working for watermelon growers is that it will help show how many heat units have accumulated over a certain period,” Miller said. “This will help growers determine when their melons may be ripe so that they can plan for harvest, which will help the growers plan for labor, equipment and so on.”
In addition to educational information, field day events also included a contest for the biggest watermelon. Clemson alumnus Sidi Limehouse of Johns Island, South Carolina, garnered first place with a melon weighing 124 pounds. Limehouse credits his monster melons to the Sunn Hemp cover crop he grew on the same plot where he grew watermelons.
“I’ve been growing watermelons since I was a teenager,” said Limehouse who is now 83. “And I learn something new every year. I learned Sunn Hemp kills nematodes and provides a lot of biomass, so I thought I’d try it and it seems to have worked.”
Limehouse isn’t content winning with a 124-pound watermelon. Next year, he hopes to bring a 150-pound watermelon and then, a 200-pound watermelon the following year. In addition to growing a Sunn Hemp cover crop, Limehouse said he takes care of his melons.
“I test my soil to be sure it has the correct nutrients,” Limehouse said. “Then, if it needs fertilizer, I make sure I apply the correct amount. I also give my melons lots of water and make sure the soil has the correct amount of carbon.”
Limehouse graduated from Clemson with a degree in agricultural engineering. He started his career growing corn and soybeans on the family farm but eventually transitioned from row crops to truck farming. Today, he operates Rosebank Farms on Johns Island, South Carolina, where he produces fruits, vegetables, flowers and herbs.
USDA-NASS South Carolina watermelon notes – The USDA National Agricultural Statistics Service 2021 State Agriculture Review for South Carolina reports state growers planted 3,900 acres of watermelon for a production value of $17,751,000.
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