The role of ethylene in kochia injury following the application of dicamba and other auxinic herbicides is not known. Experiments were conducted to evaluate kochia response to ethylene generated within plant tissue and to quantify ethylene emission from kochia following dicamba application to determine if ethylene production could be used to differentiate between dicamba-susceptible (S) and dicamba-resistant (R) kochia accessions. Dicamba at 0.28 kg ha−1 and fluroxypyr at 0.28 kg ha−1 caused severe stem and petiole twisting within 6 h of application, with S kochia exhibiting a greater level of epinasty than R kochia and fluroxypyr causing more epinasty than dicamba. Fluroxypyr provided similar control of S and R kochia, but dicamba provided less control of R kochia than S kochia. Ethylene evolution in S kochia from ethephon at 1.1 kg ha−1 and dicamba at 0.28 kg ha−1 was similar, approximately 70 ng (g fresh weight)−1 h−1. Elevated ethylene concentration from as much as 2 kg ha−1 ethephon did not produce epinastic symptoms or other plant response in S or R kochia. Ethylene evolution following dicamba application increased with time up to 48 h after application and with increasing dicamba rate up to 0.56 kg ha−1, which were the end points of the research. Ethylene evolution from the S accession was 2.5 times that of the R accession averaged across dicamba rates and harvest times. The greatest difference in ethylene evolution between S and R accessions occurred 24 h after treatment at 0.14 kg ha−1 dicamba, with S kochia producing ethylene at 470%, compared with R kochia.
Nomenclature: Dicamba; ethephon; fluroxypyr; kochia, Kochia scoparia (L.) Schad. KCHSC.