Abstract :
Spotted knapweed (Centaurea stoebe ssp. micranthos) is one of the most troublesome rangeland
weeds in western North America. As part of a larger investigation evaluating the use of
targeted sheep grazing to control spotted knapweed, we examined sheep preference and
forage quality of dried spotted knapweed in different phenological stages. We collected
spotted knapweed for preference evaluation trials from a sagebrush steppe community
near Dubois, Idaho throughout the 1999 growing season and analyzed the plants for nutritional
quality. Preference for spotted knapweed was evaluated in a cafeteria trial, where
we offered 12 ewes dried and chopped spotted knapweed in rosette, bolting, and flowering/
seedset phenological stages. Nutritional value of spotted knapweed was highest in early
phenological stages and declined with phenological development. Sheep readily consumed
spotted knapweed in all phenological stages; however, rosette and bolting knapweed were
generally selected over the flowering/seedset knapweed. Spotted knapweed consumption
was related to crude protein, and neutral detergent fiber content of spotted knapweed, yet
consumption was not related to cnicin content, a suspected feeding deterrent. This study
suggests knapweed is acceptable forage that has adequate nutritional value during the
growing season to sustain wild and domestic ungulates.
