POTENTIAL FOR CONTROLLING THE SPREAD OF CENTAUREA-MACULOSA WITH GRASSCOMPETITION

Spotted knapweed (Centaurea maculosa Lam.) is a major rangeland and ro adside weed of the northern Rocky Mountains. It is often found in plan t communities dominated by Pseudoroegneria spicatum or Festuca idahoen sis, but it rarely invades roadsides dominated by Bromus inermis Leyss . Aboveground biomass of the 3 grass species groan in mixture with Cen taurea was compared to growth in monoculture at a range of nitrogen in put levels. The results suggest that Bromus is capable of suppressing the growth of Centaurea with the degree of suppression increasing with increasing nitrogen levels. The 2 native grasses had no impact on Cen taurea under the controlled environment conditions of this study.