Isobolographic Analysis for Mixture Effects of Mesosulfuron-Methyl+Iodosulfuron with Pinoxaden in Wheat (Triticum aestivum)

Introduction: Farmers usually combine various herbicides with the aim of reducing the number of machinery passes across the field, preventing weed resistance to herbicides, and saving time and money. Combination of herbicides is not only recommended for the management of herbicide resistance, but for increasing efficacy compare with a single herbicide application and expanding spectrum weed control. Materials and Methods: In order to assess the mixing herbicides that used in wheat, several experiments were conducted in the Research greenhouse and Farm of Agricultural Faculty of Ferdowsi University of Mashhad, Iran in 2013. The greenhouse experiments were arranged in a completely randomize design with a factorial arrangement of treatments with four replications. Greenhouse studies were included two combination experiments. Experiments included of 7 doses (0, 2.25, 4.5, 9, 13.5, and 18 g ai ha-1) of mesosulfuron-methyl+iodosulfuron and (0, 5.6, 11.25, 22.5, 33.75, and 45 g ai ha-1) of pinoxaden (Axial 10% EC, EC; Syngenta, Switzerland) alone on wild oat (Avena ludoviciana Durieu) and littleseed canarygrass (Phalaris minor Rtez.). Wild oat seeds were sown in pots directly. Littleseed canarygrass seeds were placed in petri dishes with 9 cm diameter which contains a layer of filter paper then 6 ml of KNO3 solution (2 g L-1) was added to each petri dish. Petri dishes were kept for 10 days at 4 to 5 °C in the refrigerator in darkness condition and then transferred to a germinator with 20/10 °C temperature in 45/65% relative humidity for a 16/8 h day/night. Then, they were planted in 1L plastic pots filled with a mixture of clay, loam soil, and sand (1:1:1 v/v/v). The pots were irrigated every two days. The seedlings were thinned to 4 plants in per pot. The spray treatment was done at the three to four-leaf stage by using an overhead trolley sprayer (Matabi 121030 Super Agro 20 L sprayer; Agratech Services-Crop Spraying Equipment, Rossendale, UK), equipped with an 8002 flat fan nozzle tip delivering 200 L ha-1 at 2 bar spray pressure. Four weeks after spraying, the plants of the experimental units were harvested and oven-dried at 75°C for 48 h, then weighed. The greenhouse temperature varied from 18–25 °C during the day and 14–21°C at night. Field trial was conducted in completely randomized block design with three replications at Research Farm of Agricultural Faculty of Ferdowsi University of Mashhad, Iran in 2014. Because the appropriate ED50 obtained in the greenhouse therefor he recommended doses were used for field trial. Minitab 16.0 software was used for variance analysis and Mean comparison also for regression analysis, R software was applied. Results and Discussion: Greenhouse experiment results showed that pure application of mesosulfuron-methyl+iodosulfuron and pinoxaden herbicide was effective on wild oat and littleseed canarygrass. The results of mixing experiments on wild oat and littleseed canarygrass showed that mixture of mesosulfuron-methyl+iodosulfuron with pinoxaden had additive effect of both species. ED50 of different ratios of the two herbicides showed that maximum efficacy (maximum intensity effect) in decreasing dry weight of wild oat was related to ratio 100: 0 mesosulfuron-methyl+iodosulfuron and pinoxaden with ED50= 2.16 and minimum efficacy (minimum intensity effect) was related to ratio 75:25 mesosulfuron-methyl+iodosulfuron and pinoxaden with ED50= 4.22. The results of the field almost were consistent with the results of the greenhouse so that the different ratios no significant difference was observed in both species of wild oat and littleseed canarygrass. All herbicide treatments resulted in at least 85.4% and 86.86% reduction biomass and population of wild oat. Except control treatments, all tank mixing ratios of mesosulfuron-methyl+iodosulfuron and pinoxaden weren’t significantly different. On the other hand, jointed effects of the two herbicides on wild oat in field experiment had the same effect as when each herbicide applied separately. Also, comparisons between greenhouse and field results showed that twice condition have same response. The results of yield and yield components showed that parameters of grain yield and biological yield was significant at the 5% level. Conclusion: None of herbicides had effect on others and the results of greenhouse were consistent with field experiment. It may be possible without diminished performance, these herbicides were used to postpone weed resistance in weed management