Response of Kochia Selections to 2,4-D, Dicamba, and Picloram

Thirteen selections of kochia (Kochia scoparia (L.) Schrad.), self-pollinated for four generations, varied in response to (2,4-dichlorophenoxy)acetic acid (2,4-D) and 3,6-dichloro-o-anisic acid (dicamba). The most susceptible selection was injured more by 0.35 kg/ha of the dimethylamine salt of 2,4-D than the most tolerant by 0.70 kg/ha based on visual injury rating, growth in plant diameter relative to untreated controls, and seed production. The 0.28 kg/ha rate of dicamba injured the most susceptible selection as much as 0.54 kg/ha injured the most tolerant based on visual injury rating and change in plant diameter. Plant size and maturity influenced the response of kochia to herbicides, but the differences in response among selections could not be explained by variations in size or maturity. All kochia selections were tolerant to 4-amino-3,5,6-trichloropicolinic acid (picloram) at 4.28 kg/ha.