Successful quarantine efforts contain witchweed to five counties

By on August 15, 2011

August is Invasive Plant Pest and Disease Awareness Month. During the month, we’ll identify some of the invasive species found in North Carolina, highlight the department’s efforts to combat them and offer tips on how you can help reduce invasive-species populations in your area.

A portion of the witchweed root called a haustorium penetrates a corn root.

We recently spoke with Rick Iverson, weed specialist for the Plant Industry Division, about one of the invasive species the department has dealt with for more than 50 years. Iverson oversees the witchweed eradication project for the department.

Witchweed has been considered an invasive species since it was first identified in North Carolina in 1955. The weed is a parasitic plant, meaning that it attaches directly to the root systems of its host and steals valuable nutrients and water.  This has the potential to dramatically affect yields for important crops such as corn, sorghum, sugar cane and rice. While it is found just in North and South Carolina, it is considered a national threat because of the potential economic impact it could have if it were to become established in the Midwest corn belt.

Because of that concern, the U.S. Department of Agriculture Animal and Plant Health Inspection Service (APHIS) initiated a quarantine against witchweed in 1957. The program was extremely successful at containing witchweed to a relatively small area in the Carolinas. It was estimated that witchweed infested more than 433,000 acres in North and South Carolina prior to the start of the eradication program.

In 1994, APHIS assigned control of the local eradication program to the N.C. Department of Agriculture and Consumer Services. Since then, the remaining witchweed has been contained to less than 2,000 acres in Bladen, Cumberland, Pender, Robeson and Sampson counties. Iverson oversees six full-time employees and about 20 seasonal employees who conduct surveys, treat infested fields and oversee the movement of regulated articles – items that may contain witchweed seed, such as soil – to prevent the spread of witchweed across the state.

Today, less than 2,000 acres contain witchweed, down from 433,000 acres in the 1950s.

Those employees are now in the middle of their active season, and must respond quickly as they deal with tight time constraints.

“It takes 10 days between the time the plant flowers for it to release its seed,” Iverson said. “And, you don’t want the plants to seed.”

That’s because each plant can release as many as 50,000 seeds, which can then spread to surrounding uninfected areas. To combat witchweed, Iverson and his team use a two-fold process.

First, employees use herbicides to kill the witchweed. Again, timing is everything and the plants have to be sprayed while they flower. At the same time, inspectors control for the host plant. Witchweed can feed off the root systems of weedy grasses surrounding a crop. Thus, one of the inspector’s jobs is to work with farmers to make sure their fields and crop rows are properly cleared of weedy grasses.

Each year, the team surveys previously infected areas and monitors for new appearances. Witchweed can remain dormant for 10-15 years. Even if a surveyed tract of land shows no signs of witchweed this season, the plant could appear next season, which is why annual surveying is required.

“We’re helping a lot of new farmers who either aren’t knowledgeable or don’t appreciate the significance of witchweed,” Iverson said. According to Iverson, older farmers already know best practices for preventing the spread of witchweed because they have dealt with it for such a long time. However, individuals new to farming may not be as familiar with the requirements outlined by the agricultural quarantine for transporting soil, plants or machinery out of infested areas. Fortunately, the NCDA&CS Plant Industry Division is available to educate new farmers on the requirements.

Witchweed's bright-red flowers first appear in mid-July.

For now, the quarantine area is isolated to five counties in the southeastern part of the state, but there is still potential for the plant to spread to other areas. Due to the seriousness of the quarantine, APHIS offers a reward for any confirmed reports of witchweed. If you suspect witchweed in your farm, field or backyard, contact APHIS immediately a 1 (800) 206–WEED or locally at (919) 716-5590.

The witchweed flower is prominent in July, August and September. The weed is 6-12 inches tall, it has four-sided stems and narrow leaves emerging in pairs opposite each other. The bright-red flower appears in mid-July until frost.

For more information about other projects being conducted by the Plant Industry Division, go to www.ncagr.gov/plantindustry.

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