Response of Delphinium occidentale and associated vegetation to aminocyclopyrachlor and the economics of control.

摘要

D. occidentale is an important perennial weed on high elevation rangelands in the western United States where cattle are grazed because of significant losses due to toxic alkaloids. Aminocyclopyrachlor was evaluated for D. occidentale control alone and in combination with chlorsulfuron and metsulfuron-methyl at multiple rates (18, 35, 70, 140 and 315 g ai/ha) at a high elevation site in Wyoming. Aminocyclopyrachlor-containing treatments were compared with 1120 g ai/ha picloram and 63 g ai/ha metsulfuron-methyl. Treatments were replicated four times in 3 m x 12.2 m plots set in a randomized complete block design. Visual larkspur control, larkspur mortality, and visual grass injury, were collected 30 DAT. These and plant species richness, vegetation cover, and grass biomass data were collected 1 YAT. Cover data were used to calculate vegetation diversity and to assess changes in species composition associated with herbicide application. A four parameter log-logistic model was used to evaluate response variables. Aminocyclopyrachlor alone, aminocyclopyrachlor + chlorsulfuron, aminocyclopyrachlor + metsulfuron methyl provided adequate D. occidentale control and were shown to be economically viable if control last for 2 to 6 years, depending on treatment and application method. Species richness, diversity, vegetation cover, forb cover, and grass cover changed with increasing rates of aminocyclopyrachlor. Graminoid biomass was not significantly impacted by herbicide or rate. These results suggest that aminocyclopyrachlor alone or with chlorsulfuron or metsulfuron may provide satisfactory and economically viable control of D. occidentale while inducing change in the associated plant community.