sweet potato weevil

A menacing bug for its quarter-inch size, the sweet potato weevil is the most destructive insect pest of the South’s favorite potato.
Image Credit: University of Georgia Extension Service

CLEMSON — A serious pest of sweet potatoes has been confirmed in three more South Carolina counties by the Clemson University Department of Plant Industry (DPI).

The discovery of the sweet potato weevil Cylas formicarius in Jasper, Colleton and Berkeley counties likely means that a quarantine already in place in nearby Charleston and Beaufort counties will be extended to them, said Steven Long, DPI assistant director for plant protection and organic certification.

A state quarantine had been imposed on sales of certain sweet potato products in Charleston and Beaufort counties and North Carolina barred imports from Colleton County due to previous infection.

“It is important to note that none of these new finds were associated with South Carolina sweet potato growers,” Long said. “These results came from trapping stands of native morning glory throughout our coastal counties.

“Sweet potato growers may still be affected, but we are still aggressively seeking more information,” he said. “Delimiting surveys have begun and will continue through the remainder of this year.”

The reason for such wariness is the potential danger from the bug. The sweet potato weevil is one of the most destructive pests of sweet potatoes in the world, capable of causing losses of up to 97 percent in a single crop. It is widespread on every continent but Antarctica — almost anywhere sweet potatoes can be grown.

“South Carolina farmers should refrain from shipping from infected counties into other states, but also from those areas into other non-quarantined South Carolina counties,” Long said.

“It is expected that portions or all of these three new South Carolina counties will be added to our state quarantine later this year,” he said. “Additionally, North Carolina regulatory officials have been notified of the find and are expected to expand their own external quarantine on South Carolina sweet potatoes immediately.”

Long cautioned that ornamental sweet potatoes in the nursery trade are considered a huge risk for moving the pest around South Carolina and into other states. DPI asks consumers and farmers to be aware of and be vigilant for the pest.

Adult sweet potato weevils are only about a quarter of an inch long but present a mean appearance for their size. The head and wing covers of these ant-like beetles are metallic dark blue; their thorax and legs shine a bright orange red. Adult weevils feed on the exposed part of the sweet potato plant but prefer the roots, where, along with the vines, they also deposit their eggs.

“It’s important that we identify areas where the weevil is so we can partner farmers and consumers with the Clemson Extension Service to incorporate cultural practices that will lead to eradication in their fields,” Long said.

In addition to the coastal counties quarantined for the sweet potato weevil in South Carolina, North Carolina quarantines two of its own coastal counties for the pest and individual states. To the south, the entire states of Georgia and Florida are under quarantine for the weevil.

With more than 80,000 acres under cultivation for sweet potatoes, North Carolina dwarfs the production of all other states.