Weed control strategies for wheat (Triticum aestivum L.) in a cereal-legume cropping system on the Old Brahmaputra Floodplain, Bangladesh

Taslima Zahan, Md. Moshiur Rahman Mahfuza Begum, Md. Abdul Muktadir , Md. Zannatul Ferdous, Md. Enamul Haque and Richard W. Bell

Keywords:

Herbicides; Productivity; Strip planted wheat; Weed management, Pendimethalin; Pretilachlor; Triasulfuron; Pyrazosulfuron-ethyl; Ethoxysulfuron; Carfentrazone-ethyl; Carfentrazone-ethyl plus isoproturon; 2,4-D amine

Abstract:

Strip planting is a promising establishment method for wheat (Triticum aestivum L.); however, wheat yields can sharply decline if weeds in the fields are not effectively managed. Therefore, to obtain an adequate and economically-viable weed control strategy for strip-planted wheat, we conducted a study, over two years (2013-14 and 2014-15) with commercially available herbicide. Our study was in Mymensingh, in the Eastern Gangetic Plains (EGP) in Bangladesh. In the study, we used pre-emergence (pendimethalin, pretilachlor and triasulfuron), early post- (ethoxysulfuron and pyrazosulfuron-ethyl) and late post-emergence (carfentrazone-ethyl, carfentrazone-ethyl plus isoproturon and 2,4-D amine) herbicides, following a sequential application approach. Sixteen treatment combinations with these herbicides were tested in wheat, and the trials included one ‘weedy check’ and one ‘weed-free check’. The study field was predominantly infested with three grass weeds [Cynodon dactylon (L.) Pers., Digitaria sanguinalis (L.) Scop. and Echinochloa colona (L.) Link], one sedge (Cyperus rotundus L.) and five broadleaf weeds [Polygonum lapathifolium L., Physalis heterophylla (L.) Nees, Lepidium didymum (L.), Chenopodium album L. and Vicia sativa L.]. Another broadleaf weed species - ragweed (Senecio vulgaris L.) - was also in the field as a minor weed. Polygonum lapathifolium was the most dominant weed species in both years. All herbicide treatments fully controlled this species during both years, except the treatments - pretilachlor followed by (fb) hand weeding at 25 days after sowing fb pretilachlor and pretilachlor fb 2,4-D amine. The herbicide treatments reduced the total weed biomass of strip-planted wheat by 66-95% in the first year and 71-100% in the second year. With regard to the weed control efficacy, six herbicide treatments: (1) pendimethalin followed by (fb) carfentrazone-ethyl plus isoproturon; (2) pendimethalin fb ethoxysulfuron fb carfentrazone-ethyl; (3) pendimethalin fb pyrazosulfuron-ethyl fb 2,4-D amine; (4) pretilachlor fb pyrazosulfuron-ethyl fb 2,4-D amine; (5) pendimethalin fb carfentrazone-ethyl; and (6) pretilachlor fb ethoxysulfuron fb carfentrazone-ethyl were the best performing combinations. These treatments provided more grain yield than the ‘weed-free check’ by 2-19% with the economic returns increasing by 30 to 164%. Additionally, bioassay testing of the soil in the treated fields indicated that the succeeding mungbean crop was not adversely affected by the residues of herbicides applied in the previous strip-planted wheat. Overall, the study suggests that the sequential application of pendimethalin followed by carfentrazone-ethyl plus isoproturon, pendimethalin/ pretilachlor followed by ethoxysulfuron with 2,4-D amine or pendimethalin/ pretilachlor followed by pyrazosulfuron-ethyl followed by carfentrazone-ethyl would be the most effective combinations for highly effective weed control in strip-planted wheat in the EGP. Given that the wheat fields are usually rotated with rice (Oryza sativa) and mungbeans (Vigna radiata), we contend that year-wise rotational application of those herbicide treatments in strip-planted wheat might minimize the risk of herbicide resistant weed development in those crop rotations as well as in the cropping pattern.