Submitted to: Weed Technology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/23/2003
Publication Date: 4/1/2004
Citation: Ralphs, M.H., Woolsey, L., Bowns, J.E. 2004. Individual plant control of tall larkspur with tebuthiuron. Weed Technology. 18:248-251. Interpretive Summary: Tall larkspur can be controlled by broadcast herbicides on mountain rangelands, but they also kill desirable tall forbs and the herbicides are difficult to apply under aspen trees. We evaluated individual plant treatment with the pellet herbicide tebuthiuron. Application rates were based on the size of the plant and ranged from 0.1, 0.21 and 0.5 g/1000 cm2 area of the plant at waist height. The middle rate killed 62% of the plants and the high rate killed 78%. We anticipate that the high rate would give 100% mortality if the pellets were uniformly spread throughout the crown of the plant. The high clay content did not adversely affect efficacy of tebuthiuron in these individual plant applications. Bare areas left by dead larkspur plants were quickly filling in with surrounding vegetation.
Technical Abstract: Broadcast application of herbicides to control tall larkspur is difficult under aspen trees (Populus tremuloides) and most herbicides kill the desirable tall forbs that are associated with larkspur. The pellet formulation of tebuthiuron allows individual treatment of plants without injury to associated vegetation. The objective of this study was to determine effective rates of tebuthiuron for control of tall larkspur. Efficacy of tebuthiuron was first tested in the greenhouse then in preliminary field trials at label rates scaled down to individual plant treatments. All plants were killed. A replicated field trial was conducted in the mountains near Emery and Cedar City , Utah and Yampa, Colorado. The size of larkspur plants was measured and tebuthiuron was applied to the crown at 0.1, 0.21 and 0.5 g/1000 cm2 plant). The clay content of the soils or organic matter did not adversely affect efficacy.