Clemson senior Olivia Souther of Summerville spent part of her summer crisscrossing South Carolina trying to determine if the walnut twig beetle — and the fatal tree fungus that it can carry — has arrived here.
The answer is apparently no, though that could change.
The tree-killing disease has been found in Tennessee’s Morgan and Rhea counties, and it also has been found in North Carolina. Tennessee’s Division of Forestry estimates 1.38 million black walnut trees in Tennessee’s urban areas are potentially at risk — a risk that could lead to an estimated loss of $1.3 billion.
Sherry Aultman, Clemson’s Cooperative Agricultural Pest Survey coordinator, said the school put out 29 traps this summer — in about a dozen counties, from Pickens to Dorchester — to try to capture the beetle.
“We caught a lot of insects but nothing that was really even close,” Aultman said. “There are a few trees in the Upstate that are showing symptoms of decline where we can’t understand what’s going on. We’re probably going to find it at some point in time, and we’re probably going to find it soon.”
Souther, whose major is biological sciences, checked most of the 29 traps weekly during about a six month period. She picked the bugs from the scented liquid and delivered them back to a Clemson lab to be identified. The twig beetle is less than 2 millimeters in size.
Souther said this summer’s heavy rainfall posed one of her biggest challenges.
“The traps were often knocked down or overflowed with water to the point where there were no bugs to pull a sample from,” she said. “There was a lot of frustration associated with the work I put into the survey and the uncooperative weather.”
Souther said while finding no positive result could be considered disheartening, “it’s a good day when you don’t find a pest.”
Aultman said black walnut trees are native to the East Coast, though they often stopped at the fall line. Some were planted further to the coast, she added.
The twig beetle is native to the American Southwest, where it feeds harmlessly on scrubby walnut. As it moved east, it fed on black walnut — and transmitted a fungus to this species that can kill the tree in just a few years. The fungus began moving east around 2006 and was first noticed on the East Coast around 2010.
“The fungus causes cankers that cut off the flow of nutrients and water to the tree,” Aultman said. “It eventually dies from the top down. It happens pretty quickly.”
While Missouri has a black walnut industry, the tree is less common in South Carolina, where it makes up less than 10 percent of the state’s forest, she added. “People will cut it and mill it, but usually it’s because they’re logging an area and the black walnut happens to be in that area as well. We don’t have a nut industry here.”
Tennessee has placed two counties under its own quarantine because of the Thousand Cankers disease, which is transmitted by walnut twig beetles. That means residents and businesses may not move walnut tree products and hardwood firewood outside those areas.
If the beetle is ever found in South Carolina, Aultman said the state would consider similar steps to isolate it and prevent its spread.
“The quicker you can catch it, the greater the chance you have to do something about it,” she said.
This summer’s South Carolina study was paid for with about $15,000 in U.S. Department of Agriculture grant money.
Reach Robert Behre at 937-5771.