EFFECTS OF DEFOLIATION AND COMPETITION ON TOTAL NONSTRUCTURAL CARBOHYDRATES OF SPOTTED KNAPWEED

Spotted knapweed (Centaurea maculosa Lam.) is replacing native bunchgr asses and interfering with resource management objectives on many rang es in the northern Intermountain Region. Herbicides, biological contro l agents, and fire have not successfully contained spotted knapweed. S ince knapweed is grazed in some situations, effects of defoliation and competition on total nonstructural carbohydrates (TNC) of spotted kna pweed plants were determined in this study. Transplanted knapweed plan ts were grown for 6 months in a greenhouse under 3 levels of competiti on with bluebunch wheatgrass (Pseudoroegneria spicata [Pursh] Love) an d 3 levels of defoliation. Total nonstructural carbohydrates (pool and concentration) were determined at the end of the experiment. Concentr ation and pools of carbohydrates generally varied among stems, roots, crowns, and with monthly defoliations. Importance of stems for carbohy drate storage was more evident in analyses of pools rather than concen trations. Monthly defoliations decreased carbohydrate concentrations b y about 50%, and pools by about 80% respectively within stems, roots, and crowns. While competition from bluebunch wheatgrass influenced tot al nonstructural carbohydrates concentrations, it did not influence po ols. Although frequent defoliations of spotted knapweed reduced carboh ydrates, other factors probably limit the feasibility of using grazing animals to control spotted knapweed on native bunchgrass ranges in we stern North America.