Threadleaf Groundsel and Forage Response to Herbicides in the Davis Mountains.

Sprays of 2,4-D + picloram (4:1), 2,4,5-T + picloram (1:1), or picloram alone at 1.1 kilogram per hectare (kg/ha) in fell or winter effectively controlled threadleaf groundsel on Deep Upland and Igneous Hill and Moun tain range sites in the Davis Mountains. Tebuthiuron applied as sprays of wettable powder in water or pellets at 1.1 kg/ha during summer reduced threadleafground sel densities by 99 to 100 percent for almost 20 months after treatment, but applications at other seasons were not effective. Sprays of 2,4-D, dicamba, or 2,4-D + dicamba (3:1) at 1.1 kg/ha and pelleted picloram at 1 1 kg/ha did not effectively control threadleaf groundsel. Fall or winter applications of the foliar-active herbicides were generally more effective for threadleaf groundsel control than were spring or summer applications, pre sumably because the plants were actively growing in the fell and winter. Blue grama and associated grasses were damaged by summer applications of most herbicides but recovered during the subsequent growing season.