Investigating the Effect of U46 Combi Fluid and Bromicide MA Herbicides in Different Growth Stages of Winter Wheat (Triticum aestivum L.) on Weeds Control and Yield of Dryland Wheat

IntroductionWheat (Triticum aestivum L.) is important in the food regime of three-quarters of the world's population because it is nutritious and cheap compared to other similar foods. The competition between wheat and weeds is considered as one of the most important limitations of global wheat production. In Iran, weeds are of particular importance in reducing wheat yield, and according to the surveys, the average damage caused by weeds in the country's wheat fields is 23%. The most common way to manage wheat weeds is herbicide application. Every crop resists herbicides at a given growth stage, otherwise, herbicide application will damage the main crop. In recent years, the most frequent broadleaf herbicides used for weed chemical control in wheat are 2-4-D + MCPA (U46 combi fluid). To apply the 2,4-D herbicide, wheat should be at the tillering to the appearance of the first visible node stage. Application of 2,4-D after the first node will cause spike deformation and yield reduction due to the adverse effect of herbicide on sporogenesis. This study investigated different application times effects of 2-4-D + MCPA (U46combifluid) and Bromoxynil + MCPA (Bromicide MA) on winter wheat yield and weed control. The study aimed to determine the application time of the best herbicide with minimal damage on dryland wheat.Materials and MethodsTo investigate the effect of hormone herbicides on weeds and the yield of dryland bread wheat in different vegetative growth stages in cold dryland areas, a field experiment was conducted as a randomized complete block design arrangement with four replications during 2021-23 cropping seasons at the Dryland Agriculture Research Institute, Maragheh, East Azerbaijan. Treatments included the application of 2-4-D + MCPA (U46combifluid) and Bromoxynil + MCPA (Bromicide MA) (1.5 L ha-1) at the tillering (Z29), the 2nd   node (Z32), and the booting stages (Z45) with two control treatments of weeding (weed infested) and no weeding (weed free). The Varan wheat cultivar was sown at a depth of 4–6 cm with a seeding density of 380 seeds per square meter. To evaluate weed type and density (plant m-2), sampling was done 30 days after herbicide application. The crop was harvested at full maturity to collect data for grain yield and a thousand grain weight and grain/spike. After checking the normality of the data, they were analyzed with GenStat (V.12) software and the mean comparison was performed by the Least Significant Difference (LSD) test at the 5% probability level.Results and DiscussionThe results indicated that the weed growth time is affected by the rainfall in dryland conditions so that in the 2021-2 year, the main spring precipitations occurred in May while in the 2022-23 year, it happened in April. Therefore, for the first cropping season, the highest weed density was recorded in the second   node stage whereas at the tillering stage in the second cropping season. In the first year, due to lower rainfall, and drought stress, a further decrease in wheat yield was observed in response to the delayed herbicide application so that it was higher in the 2-4-D + MCPA herbicide treatment. In the 2021-22 year, the lowest yields were recorded for 2-4-D + MCPA and Bromoxynil + MCPA herbicides in the booting stage with 1568 and 1710 kg ha-1, respectively. In the 2022-23 year, the lowest grain yield was observed for 2-4-D + MCPA in the second node, and booting stages, respectively, 1701 and 1747 kg ha-1.ConclusionBased on the results, wheat is more sensitive to delayed application of 2-4-D + MCPA and reduces wheat yield more, in contrast, it is more tolerant to bromoxynil + MCPA herbicide (Bromicide MA), and it can be applied up to the 2nd node stage (Z32).