The University of Arizona

Sheep grazing spotted knapweed and Idaho fescue.

B.E. Olson, R.T. Wallander


Spotted knapweed (Centaurea maculosa Lam.), an Eurasian perennial forb, is replacing many native perennial grasses, such as Idaho fescue (Festuca idahoensis Elmer.), throughout the Northern Rocky Mountain region. Our objective was to determine sheep use of spotted knapweed and Idaho fescue during 3 consecutive summers (1991-1993). Each summer, 3 small spotted knapweed infested pastures were grazed for 5-8 days in mid-June, 2-6 days in mid-July, and 1-6 days in early September. Nutritive value of spotted knapweed leaves and flowerheads were consistently higher than of Idaho fescue. Nutritive value for both species declined as the summer progressed. The sheep readily grazed spotted knapweed, but they also grazed other plants, including the native Idaho fescue. They did not consistently graze 1 species more than another, which may have reflected daily weather patterns, slight differences in forage nutritive value, or cyclic grazing patterns which are often associated with plants containing secondary compounds, such as spotted knapweed. At the end of many grazing periods, heights of grazed spotted knapweed plants were greater than those of Idaho fescue, which reflected how the sheep grazed leaves and avoided fibrous stems of mature spotted knapweed plants, whereas they were not selective when grazing Idaho fescue. Although the sheep did not graze spotted knapweed exclusively, probably because animals seek diverse diets, their use of this noxious weed may help restore a balance in competitive relations between this noxious weed and native grasses.



noxious substances;cnicin;Festuca idahoensis;weed palatability;leaves;canopy gaps;stems;ambient temperature;weed control;fiber content;rain;selective grazing;crude protein;sheep;in vitro digestibility;centaurea maculosa;seasonal variation;introduced species;invasive species;nutritive value;feeding preferences;plant height

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