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Thesis (M.S.)—University of Nebraska—Lincoln, 1972. Department of Agronomy.


Copyright 1972, the author. Used by permission.


Musk thistle (Carduus nutans L.) has been the subject of intensive efforts at control in Nebraska since it was recognized as a major threat to pasture and rangelands in the late 1950’s.It was placed on the Nebraska noxious weed list by the Legislature in 1959, and is also considered noxious by official act of most surrounding states.Some early studies of methods to control it were published in New Zealand in 1955, 1960, 1961, and 1962 (1, 2, 3, 15), and in Nebraska in 1964, 1965, and 1968 (12, 7, 4, 5).Control methods using herbicides were most effective when plants were seedlings or undergoing active vegetative growth in the rosette stage.

For many reasons, attempts at control are often delayed until the rosettes have bolted, and the plants have formed buds or begun to bloom (Figures 2 and 3).The effects of commonly used herbicide or mowing treatments at these later stages of maturity were generally observed to be variable, and the relative value of such efforts was not clear.Guidelines are needed by those concerned with economic control of musk thistle.Reports have been received of unpublished work performed in a neighboring state, which indicate that treatment with [(2,4-dichlorophenoxy) acetic acid] 2,4-D at bud and bloom stages may nearly eliminate production of viable seed from musk thistle in that state.Field observation of similar treatments attempted in Nebraska indicate that such results would probably occur rarely, if at all in Nebraska.These considerations prompted the studies reported in this paper.

The objectives of the experiments were:(a) To determine the reduction in numbers of viable seed produced by musk thistle following treatment at later stages of maturity with kinds and rates of herbicides in common use.(b)To determine the effects of mowing at the later stages of maturity on production of viable seed by the mowed stalks and by any regrowth.(c)To determine the stage of maturity at which terminal heads on mowed stalks of musk thistle might already contain viable seed, and how the amount of viable seed produced from such heads might increase with maturity at the time of mowing.

Advisor:M. K. McCarty