Control of Rayless Goldenrod (Isocoma wrightii) with Soil-Applied Herbicides

Picloram (4-amino-3,5,6-trichloropicolinic acid) applied at 0.6 to 1.2 kg/ha as 5 or 10% pellets during the summer or fall usually killed 90% or more of the rayless goldenrod [ Isocoma wrightii (Gray) Rydb.] on sandy loam soils in western Texas, whereas the higher rates were necessary for 80% or greater control following winter applications. Acceptable control persisted for 4 yr. Applications of tebuthiuron { N -[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]- N,N′ -dimethylurea}at 1.1 kg/ha as 20% pellets during summer controlled 85% of the rayless goldenrod, but summer applications of tebuthiuron at 0.6 kg/ha or winter applications at 0.6 or 1.1 kg/ha did not control the weed effectively. Dicamba (3,6-dichloro- o -anisic acid) applied at 0.6 or 1.1 kg/ha as 5% granules did not control rayless goldenrod. Prescribed burning in late February reduced the density of rayless goldenrod 18 to 41%, but decreased control with soil-applied picloram or tebuthiuron. Reduction in rayless goldenrod densities of 75% or greater following applications of picloram or tebuthiuron pellets more than doubled the estimated carrying capacity of the arid rangeland.