South Carolina: Sweet Potato Weevil, Benghal Dayflower Quarantine Areas Increased

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

Clemson University’s Department of Plant Industry (DPI) has issued updated quarantine information related to two crop pests: sweet potato weevil and Benghal dayflower.

The agency expanded a longstanding quarantine due to sweet potato weevils in Charleston and Beaufort counties to include Jasper, Colleton and Berkeley counties.

The agency also increased an area of quarantine in Aiken County due to Benghal dayflower. The original quarantine was implemented in November 2016. The area now includes a section forming a triangle from north latitude 33.380, east to U.S. Highway 1, south to U.S. Highway 125 and north back to north latitude 33.380.

Both pests are serious threats to agricultural crops.

Aiken County Benghal dayflower quarantine area.

Aiken County Benghal dayflower quarantine area. Click Image to Enlarge

The sweet potato weevil is one of the most destructive pests to 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.

The quarantine expansion is the result of an ongoing survey which shows the weevil has moved outside the original quarantine area. Sweet potato weevils are mobile and can overwinter on native Ipomea plants like morning glory.

Clemson DPI has surveyed 100 percent of production fields for many years across the state in hopes of catching the pest before it was widespread. To date, the pest has not been found in any field crop trapping of uninfested counties.

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“Early detection and eradication is the first line of defense when it comes to invasive species. In 2018, Clemson DPI set out to contain the pest before it could spread far and wide. That’s why DPI implemented a roadside trapping effort last year and, unfortunately, we discovered that it’s moved a little farther than we thought,” said Steven Long, assistant director of Clemson DPI.

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.

Benghal dayflower competes with row crops like soybeans, corn, cotton and peanuts for nutrients. It can establish itself fairly easily and typically spreads with agricultural equipment, such as tillers and harvesters. Farmers with infected fields in the quarantine area are restricted from moving their farm equipment without first cleaning it to remove possibly infested soil. They must document the cleaning.

Benghal dayflower infestation in cotton field. Photo: Stanley Culpepper, University of Georgia, Bugwood.org

“We have an extensive list of known fields actively infested with Benghal dayflower, but seeds can sometimes lie dormant for many years before being disturbed and germinating. We believe that is what happened here and led to a later find outside of our original quarantine boundaries. These quarantine efforts are working in preventing contaminated equipment movement, which is what we believe is the primary means by which this invasive weed moves,” Long said.

Benghal dayflower, or Commelina benghalensis, is identifiable by its egg-shaped leaves, red hairs on the leaf sheaths and small flowers. The flowers have three petals: two purple and one white. DPI asks for the public’s assistance in detecting this damaging weed.

If an infestation is suspected, contact the Department of Plant Industry at 864-646-2140 or invasives@clemson.edu or contact a local Clemson University Cooperative Extension Service office.

While the weed is pretty to look at, it can spread rapidly because it produces seeds both above and below ground and can thrive in both wet and dry conditions. It is also tolerant to glyphosate, the active ingredient found in Roundup, Rodeo, Accord and other pre- and post-emergent herbicides.

The weed prefers wet areas but can thrive in dry conditions as well. Additionally, Benghal dayflower is tolerant to many herbicides and can be a significant problem for Round-up Ready crops.

DPI reviews its quarantines annually after each inspection and survey season to determine if expansions are needed.  For more information on these and other invasive pests, visit the Clemson University Public Service and Agriculture’s Invasive Species Program website.


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