A carpeted roller applicator and broadcast sprayer were compared for application of glyphosate, metsulfuron, and picloram to control duncecap and tall larkspur on mountain range sites in southern Idaho and central Utah, respectively. Glyphosate was the most effective herbicide, controlling 96% of both larkspur species when applied by the sprayer and 78% when applied by the roller. There was no difference in larkspur control between application methods using metsulfuron or picloram. Application of herbicides by the carpeted roller was less detrimental to forbs compared to the sprayer, and the roller application of glyphosate did not reduce grass cover. Grass cover doubled following treatments with picloram and metsulfuron.

Several herbicides were evaluated for their ability to control duncecap larkspur, a serious poisonous plant on mountain rangelands in the western U.S. Duncecap larkspur density was reduced from 33 to 93% by triclopyr applied at 2.2, 4.5, and 9.0 kg ae/ha. Picloram applied at 2.2 and 4.5 kg ae/ha reduced density from 33 to 99%. Metsulfuron applied at 86 and 138 g ai/ha reduced density from 50 to 98%. Glyphosate was the most effective herbicide, reducing density by 90 to 100% when applied at 2.2 kg ai/ha. Glyphosate reduced the cover of grasses and perennial forbs but increased cover of annual forbs. All rates of picloram and metsulfuron reduced forb cover. Grass cover increased in most plots where duncecap larkspur and forbs were reduced.

Timing and application rates of herbicides were evaluated for control of duncecap and tall larkspur on mountain rangelands. Picloram, triclopyr, glyphosate, and metsulfuron were applied at three rates during three growth stages (vegetative, bud, and flower) to evaluate the rate by growth stage interaction. Picloram was equally effective over all growth stages when applied at 1.1 or 2.2 kg ae ha−1. Metsulfuron was most effective when applied in the vegetative stage; 0.035 kg ai ha−1 killed 95% of duncecap larkspur, but 0.14 kg ha−1 was required to kill the same percentage of tall larkspur. Glyphosate at ≤ 2.2 kg ai ha−1 was least effective when applied in the flower stage compared to earlier growth stages. Triclopyr showed variable control at rates from 1.1 to 4.5 kg ae ha−1.