Response of a Sulfonylurea (SU)-Resistant Biotype of Limnophila sessiliflora to Selected SU and Alternative Herbicides

Abstract

Sulfonylurea (SU) herbicides, known for their high herbicidal activity and low mammalian toxicity, were used since 1988 to control Limnophila sessiliflora and other broadleaf weeds on rice fields at Sennan Village, Akita Prefecture, Japan. Since 1996, control of L. sessiliflora with the SU herbicides was no longer satisfactory. Two greenhouse studies at Tohoku National Agricultural Experiment Station and one experiment in the rice fields at Sennan Village were conducted in 1997 to confirm L. sessiliflora resistance to SU herbicides and to compare herbicide treatments for control of SU-resistant L. sessiliflora . Greenhouse studies showed that the L. sessiliflora biotype from Sennan Village was cross-resistant to four SU herbicides, including bensulfuron-methyl (BSM), pyrazosulfuron-ethyl (PSE), imazosulfuron (IMS), and ethoxysulfuron (ETS). The resistant biotype was 300–900 times more resistant to SU herbicides than the susceptible biotype from Omagari, Akita based on GR 50 (50% growth reduction) values. Standard treatments of pretilachlor and pentoxazone or mixtures of simetryn + MCPA-thioethyl, ETS + pyrazolate + pretilachlor, BSM + cafenstrole + daimuron, and BSM + daimuron + cafenstrole + azimusulfuron applied postemergence controlled SU-resistant L. sessiliflora . In the field experiment, mixtures of IMS + cafenstrole + daimuron and BSM + mefenacet failed to control L. sessiliflora , but herbicide treatments controlling SU-resistant L. sessiliflora included postemergence applications of mixtures of esprocarb + dimethametryn + PSE + pretilachlor and BSM + thiobencarb + mefenacet and sequential applications of pretilachlor/thiobencarb + simetryn + MCPB, pretilachlor/bifenox + SAP, pretilachlor/MCPA-thioethyl + simetryn, and pretilachlor/BSM + thiobencarb + mefenacet. Our results suggest that the SU-resistant L. sessiliflora had not developed multiple resistances to herbicides with different modes of action. In particular, amide or phenoxy herbicides were effective control measures.