Author
Jerome F. Grant
jgrant@utk.edu
University of Tennessee
Knoxville
Abstract
Musk thistle (Carduus nutans), native to Europe, Asia, and northern Africa, was introduced to North America in the mid-1800s—likely as an ornamental plant or through contaminated ship ballast. Since then, it has spread widely across the United States, where it has posed significant challenges for decades, especially in the southern Appalachian region. Now classified as an invasive weed, it has been established in Tennessee since the early 1940s. It invades pastures, natural areas, roadsides, and urban spaces, reducing land use value and incurring high management costs. Herbicide treatments are costly, and widespread infestations make seed dispersal and reinfestation difficult to control — a single seed head can produce up to 1,000 seeds, and a single plant up to 10,000. In the early 1990s, a biological control programme was launched in Georgia, North Carolina, Tennessee, and Virginia, introducing two European weevil species: Trichosirocalus horridus and Rhinocyllus conicus. Both are now established in Tennessee, where they have contributed to an estimated 90% reduction in musk thistle populations. Our integrated pest management (IPM) strategy now combines mowing, targeted herbicide use, and biological control. This approach in Tennessee has resulted in effective long-term control, saving over $5 million annually in reduced management costs and increased land values. This poster explores the benefits and risks of this biocontrol programme, three decades after its
Keywords
Musk thistle
Integrated pest management
Weevils
Benefits
Risks
Highlights
Assessment of short- and long-term benefits/risks of biological is limited by adequate funding.
Musk thistle is managed using biological control, targeted herbicides, and mowing (effective IPM).
IPM incorporating biological control is essential for effective management of some invasive plants.