Jr. Lacey et al., EFFECTS OF DEFOLIATION AND COMPETITION ON TOTAL NONSTRUCTURAL CARBOHYDRATES OF SPOTTED KNAPWEED, Journal of range management, 47(6), 1994, pp. 481-484
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.