Verification of the resistance of Echinochloa colona populations to the formulation of Imazapic + Imazapyr herbicides that inhibit ALS (acetolactate synthetase) and alternatives for its chemical control in rice (Oryza sativa L.)

Three experiments were carried out in a mesh house and one in the field, with the purpose of verifying the resistance of five populations of Echinochloa colona to the formulated mixture of the herbicides Imazapic + Imazapyr, inhibitor of ALS (acetolactate synthase) and to identify effective chemical treatments for your control. The mesh house experiments were carried out in the mesh house of the Departamento de Malezas from Estacion Experimental Agricola Fabio Baudrit Moreno (EEAFBM), La Garita, Alajuela, while the field experiments, in the Hacienda Mojica farm, Bagaces, Guanacaste. The first experiment consisted of the resistance test, where 5 populations of Echinochloa colona were used from sites where there was poor control with these herbicides and a population from the EEAFBM, where these herbicides had not been used. Increasing doses of Imazapic + Imazapyr herbicides were applied, the doses of the commercial formulation used were 159.6 g a.i./ha (228.0 g PC/ha), 319.2 g a.i./ha (456.0 g PC/ha), 638.4 g a.i/ha (912.0 g PC/ha), 1276.8 g a.i./ha (1824.0 g PC/ha). For resistance evaluation, the parameters used were fresh weight and degree of damage on a scale of 0 to 5 at 30 days after application. Five of the six populations of E. colona evaluated presented plants with healthy tissue even at the highest dose evaluated of the Imazapic + Imazapyr herbicide mixture (1276.8 g a.i./ha), for which they were determined to be resistant to this herbicide; The population of E. colona collected in the EEAFMB turned out to be susceptible, all plants dying when applied with the commercial dose (159.6 g a.i./ha). For the second and third experiments, the three populations that presented the highest fresh weight of the living tissue of the E. colona plants that received the highest dose of the herbicide (1276.8 g a.i./ha) were selected; these populations were Pali, Mojica and Bolero inside. The second experiment consisted in evaluating the efficacy of the pre-emergent herbicides pendimethalin (750 g ai/ha), oxyfluorfen (360 g ai/ha), oxadiargyl (200 g ai/ha), butachlor (3000 g ai/ha) and thiobencard (2880 g ai/ha). All the pre-emergent herbicides evaluated showed total control of the three populations of E. colona included in this study. In the third experiment, the post-emergence herbicides propanil 3360 ai/ha, fenoxaprop-p-ethyl 145 g ai/ha, cyhalofop 225 g ai/ha, profoxydim 176 g ai/ha, bispyribac sodium 104 g ai/ha and quinclorac 450 g ia/ha were tested. Profoxydim, quinclorac, cyhalofop, fenoxaprop-p-ethyl and bispyribac sodium were effective in controlling the three evaluated populations of E. colona with resistance to Imazapic + Imazapyr, without significant differences between them, but with respect to the control without herbicide and to propanil. Of the herbicides evaluated in experiments 2 and 3, those that presented the greatest efficacy were selected and field tests were carried out; in addition, two treatments used on the farm were added. The treatments evaluated were pendimethalin pre 1500 g ai/ha, thiobencard pre 2700 g ai/ha, oxyfluorfen pre 720 g ai/ha, pendimethalin pre 1500 g ai/ha + quinclorac post 400 g ai/ha, pendimethalin pre 1500 g ai/ha. ha + profoxydim 160 g ai/ha, thiobencard pre 2700 g ai/ha + quinclorac 400 g ai/ha, thiobencard pre 2700 g ai/ha + profoxydim 160 g ai/ha; in early post treatment clomazone 384 g ai/ha + the formulated mixture of propanil + anilofos 1320 g ai/ha + 12 g ai/ha, quinclorac 400 g ai/ha, profoxidim 160 g ai/ha, Imazapic 39.9 g ai/ ha + Imazapyr 119.7 g ai/ha. The treatment that presented the lowest number of plants/m² and the highest control percentage of E. colona (90%) was pendimethalin 1.5 kg/ha applied pre-emergence + quinclorac 0.4 kg/ha post-emergence. However, with other treatments As thiobencard pre + quinclorac post, pendimethalin pre + profoxydim post, quinclorac post and clomazone pre + propanil + anilofos post, control percentages higher than 80% were obtained. Oxyfluorfen and thiobencard applied preemergence were not effective in controlling E. colona. The lot in addition to have a high incidence of E. colona, also presented a relatively high weedy rice population, which could not be controlled, therefore it was decided to evaluate the number of red rice or weedy rice/m² panicles prior to harvest; the treatment with Imazapic + Imazapyr was the one that presented significantly the lowest number of weedy rice/m² panicles. The best field yield was with Imazapic + Imazapyr. It is concluded that the 5 populations of E. colona from sites with poor control showed resistance to the mixture of the formulated herbicide Imazapic + Imazapyr, and at the same time it was found that these populations can be effectively controlled with pre-emergent and post-emergent herbicides commonly used in rice