Kochia scoparia Growth Response to Triazine Herbicides

Greenhouse-grown kochia [Kochia scoparia (L.) Schrad. # KCHSC] seedlings from populations having either a 13-yr triazine history or no triazine history were sprayed postemergence with 0, 2, or 20 kg/ha atrazine [6-chloro-N-ethyl-N′-[1-methylethyl)-1,3,5-triazine-2,4-diamine]. Fresh weight was reduced 20% in triazine history kochia treated with 20 kg/ha atrazine. Seedlings with no triazine history were killed by 2 kg/ha atrazine. Biotypes resistant to atrazine were also resistant to five other triazine herbicides. Biotypes susceptible to atrazine were susceptible to the other triazines. Atrazine-resistant biotypes were more susceptible to 2,4-D [(2,4-dichlorophenoxy)acetic acid] than atrazine-susceptible biotypes, but atrazine history had no effect on response to diuron [N′-(3,4-dichlorophenyl)-N,N-dimethylurea].