New pest found in Darlington County forces some states to quarantine S.C. sweet potatoes

DARLINGTON — A new pest detected in two farm fields in Darlington County has resulted in a quarantine of South Carolina sweet potatoes by Louisiana and Mississippi.

Guava root-knot nematode was detected in the Darlington County fields during a routine survey by Clemson University’s Department of Plant Industry (DPI) in September 2017 and confirmed by the U.S. Department of Agriculture in January 2018.

Louisiana has prohibited the import of fresh market sweet potatoes and sweet potato seeds and slips from South Carolina. The state also is blocking the entrance of soil from South Carolina. In addition, all South Carolina commercial planting and harvesting equipment entering Louisiana must be accompanied by a DPI-issued certificate of inspection. All South Carolina nursery stock entering the state must have a soil sample and certificate from DPI indicating the sample is free of the nematode.

Mississippi has applied the same restrictions, but specific to Darlington County rather than statewide.

Steven Long, DPI assistant director for plant protection and organic certification, said farmers of the fields where the nematode was found are cooperating and restricting crop and equipment movement where it could present a risk for pest spread.

“For all practical purposes, the quarantine affects all soil, all nursery stock and any equipment that’s ever been in South Carolina soil. So, while it is a quarantine based on sweet potatoes, these states are also trying to protect cotton and soybeans,” Long said.

Because the nematode’s range in the Southeast is currently unknown, Long said DPI will conduct a statewide two-part survey to determine how widespread it is in South Carolina. A market-based survey will test sweet potatoes on store shelves, and a field-based survey will test more than 10 percent of all South Carolina fields where sweet potatoes have been grown since 2016. DPI will issue its findings shortly after the survey is completed.

Because the quarantine could expand to other states, Clemson DPI has created a webpage to keep growers up to date with the latest information.  It’s also possible, pending survey results, that South Carolina will enact its own quarantine later this year. Quarantine updates will be posted to http://clemson.edu/regulatory/grkn.

According to an article by the LSU Ag Center, the guava root-knot nematode (Meloidogyne enterolobii) is considered to be the most damaging root-knot nematode in the world “because of its wide host range, aggressiveness, and ability to overcome the resistance that has been developed against root-knot nematodes in many crops.”

North Carolina, which has 80,000 acres of sweet potatoes under cultivation, has issued a self-imposed quarantine. While the North Carolina quarantine does not restrict the movement of fresh market sweet potatoes for sale for consumption, Long said it could be problematic for South Carolina growers.

“As recently as the 2018 growing season, South Carolina farmers acquired slips from North Carolina that were both not certified and contained some roots and soil,” Long said. “Going forward, access to these slips will be greatly restricted if not completely unavailable. The North Carolina quarantine will have the greatest impact on our growers because most of them get their planting stock from North Carolina. In all likelihood, cost of that planting stock will skyrocket because of these new regulations and the required certifications.”

Clemson University is working with nematologists in Georgia, North Carolina and Florida to investigate the nematode’s distribution in those states, screen for potential genetic resistance to the nematode in sweet potatoes, cucurbits and tomatoes, and design protocols for managing the pest in crops.