Controlling Tall Larkspur on Snowdrift Areas in the Subalpine Zone

Abstract

Repeated annual applications of 2,4,5-T [(2,4,5-trichlorophenoxy) acetic acid] or silvex [2-(2,4,5-trichlorophenoxy) propionic acid] reduced the density of tall larkspur (Delphinium barbeyi (Huth) Huth) below a level that is potentially dangerous to grazing cattle. Killing tall larkspur and other forbs resulted in a plant community dominated by grasses. The dominant species of grass depended on whether the treated plot was grazed by cattle. Letterman needlegrass (Stipa lettermanii Vasey) dominated on grazed plots and mountain brome (Bromus carinatus Hook. & Arn.) dominated when plots were protected from grazing cattle. Reinvasion of treated areas by tall larkspur and the unpalatable weedy species occurred more rapidly on grazed plots than on ungrazed plots.