A replicated field trial was conducted to determine the effective rates of tebuthiuron for control of individual tall larkspur plants in the mountains near Emery, UT, Cedar City, UT, and Yampa, CO. The size of larkspur plants was measured, and tebuthiuron was applied to the base of each plant at 0.1, 0.21, and 0.5 g product/1,000 cm2 of foliar crown cover. Tebuthiuron at 0.21 g/ 1,000 cm2 rate controlled 62% of the plants. Tebuthiuron at 0.5 g/1,000 cm controlled 78% of the plants (2.5 g for an average-sized plant of 5,000 cm2). The high clay content of the soils at Emery or high organic matter content of soils at Cedar City or Yampa did not adversely affect efficacy.
Nomenclature: Tebuthiuron; tall larkspur, Delphinium barbeyi Huth #3 DELBA.
Additional index words: Cattle poisoning, poisonous plant.
