Document Type

Thesis - Open Access

Award Date


Degree Name

Master of Science (MS)

Department / School



Two sites in southeastern South Dakota were used in this study. Both sites supported unusually dense infestations of C. nutans and were chosen on that basis. Site A was located at an unoccupied farmstead in Minnehaha County, 2 miles S.W. of Crooks. This site was composed of 3 distinct infestations of musk thistle: (1) the first stand of thistles was approximately 2 x 9 m surrounded by Siberian elm, Ulmus pumila L., Conyza canadensis (L.) Cronquist (mare's tail) and a Bromus sp., probably B. inermis Leysser. The thistles in this area stood 2+ m tall at maturity. (2) The second area, 3 x 3 m, was composed of musk thistles shaded throughout the day by Fraxinus pennsylvanica Marshall and Acer negundo L. The thistles in this area had been knocked down at an undetermined date early in the first summer of the study. In the second summer, only few thistles were found in this area being replaced largely by catnip, Neoeta catapia L. (3) The third area at Site A was a narrow band of musk thistle approximately 2 x 20 m, growing along a cornfield adjacent to the unoccupied farmstead. These thistles were 1 m tall at maturity and were subjected once, in the early summer of 1973 to pesticide wind drift from the contiguous cornfield, which resulted in permanent twisting of the stems, although the drift was not strong enough to initiate any kind of kill. Site B was a 30-acre pasture, 10 miles west of Yankton and 1 mile north of the Missouri River. The thistle density of this pasture was not as high as the densities of the stands of Site A, but the infested area was much more extensive, covering about 50%, of the field. The principal grasses of this pasture were: Sporobolus cryptandrus (Torrey) Grey, B. inermis, B. japonicus Thunberg, Poa pratensis L., and Panicum wilcoxianum Vasey. The field was sprayed with herbicides twice in 1974. The first application, with 2,4-D, occurred on 14 June. About 20 of the musk thistles remained alive. The second application occurred between 24 July and 7 August. Virtually 100% of the musk thistle were killed. The sampling techniques of ecological studies dictate the nature and accuracy of the entire study. In my work, the wide variation in habitats of musk thistle, the absence of faunistic records of C. nutans in South Dakota, and the limited duration of this study, called for a broad, flexible procedure that would produce qualitative results on which to base more specific studies if necessary. Results from my survey should reveal the success or failure of this initial introduction of R. conicus and at the same time divulge some of the insect fauna of musk thistle in South Dakota.

Library of Congress Subject Headings

Weeds -- Control

Thistles -- South Dakota



Number of Pages



South Dakota State University