Ericameria austrotexanaand Associated Range Forage Responses to Herbicides

Abstract

Canopy cover of false broomweed (Ericameria austrotexanaM.C. Johnston) on the Rio Grande Plains of Texas was initially reduced by 96% by glyphosate [N-(phosphonomethyl)glycine] applied at 2.2 kg/ha in the spring. Acceptable control of this shrub with glyphosate lasted at least 4 yr. Glyphosate severely reduced basal cover of perennial grasses during the year of treatment, but grasses completely recovered within 2 yr after treatment. Standing forage crop increased by an average of 83%, compared to untreated areas, and livestock carrying capacity increased from 1 animal unit (AU)/13 ha to 1 AU/7 ha. Picloram (4-amino-3,5,6-trichloropicolinic acid), paraquat (1,1′-dimethyl-4,4′-bipyridinium ion), and paraquat plus atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] applied in the spring were less effective than glyphosate. Canopy reductions of false broomweed 6 months after applications of 2.2 kg/ha of picloram, paraquat, or paraquat plus atrazine were equivalent to that from 1.1 kg/ha of glyphosate, and control with these herbicides was usually restricted to the season of application. Dicamba (3,6-dichloro-o-anisic acid), 2,4-D-[(2,4-dichlorophenoxy)acetic acid], atrazine, and 2,4-D plus atrazine were not effective when applied in the spring or fall. Time required for recovery of false broomweed canopy apparently varied with amounts of rainfall received after herbicide application.