Kendall, Deborah M. 1995. Biocontrol Pest Management for Thistles in Wind Cave National Park. Annual Report; Proj. No.: WICA-R92-0200; Coop Agreement:CA 1268-1-9016; Work Order: FLC 10.
The biocontrol for suppression of the Canada thistle, Cirsium arvense L. in Wind Cave National Park for 1994 focused on the following objectives:
(1) Release and monitoring of populations of Ceutorhynchus litura (Coleoptera: Curculionidae).
(2) Release and monitoring of populations of Larinus planus, the seedhead weevil of Canada thistle.
(3) Release and monitoring of the thistle gall fly, Urophora cardi (L.)(Diptera: Tephritidae).
(4) Monitoring of local populations of Rhinocyllus conicus Froel. (Coleoptera: Curculionidae).
(5) Monitoring of invertebrate species and populations of Canada thistle.
Thistles belong to a complex of several genera that share many characteristics including numerous sharp, stiff spines on the leaves stalks, and flowers. This characteristic alone causes considerable nuisance to people and animals, especially in an area of high use such as a National Park (Currie 1984). The most common exotic thistle pest in Wind Cave National Park is the Canada thistle C. arvense which competes for resources with native plant species. Canada thistle is native to Europe and was introduced into the United States in the 19th century (dunn 1976). A foriegn species is introduced without its natural complement of herbivores and pathogens and withour intervention the thistle will spread at an alarming rate (Hodgson 1968). According to National Park Service policy, alien species should be controlled and eventually eradicated if possible (National Park Service 1978).
Options for the control of canada thistle include herbicide application, mechanical suppression or biological control. Herbicide use is not an option at Wind Cave National Park because it is situated above a natural cavern. Herbicide run-off from above-ground habitats would contaminate the plant and animal communities of the caverns. Herbicide application also stimulates the development of herbicide resistant biotypes of exotic plant species and poses a threat to the health of people and animals within the park. In addition, complete removal of an invading exotic plant species through herbicide control leads to soil erosion and depletion of resources for wildlife than depend on the plants for forage (Westman 1990). Control of Canada thistle by mechanical methods is difficult because growth occurs readily from adventitious roots and mechanical control serves to stimulate increased vegatative growth closer to the ground.