Evaluation of the Effect of Mixing Clopyralid with Oxadiazon and Oxadiargyl on Control of Broadleaf Weeds in Rapeseed (Brassica napus L.)

Abstract

IntroductionRapeseed is one of the most important crops cultivated for oil extraction and has the highest annual growth rate (in terms of production) among the essential oilseeds in the world. Due to its slow growth rate, the rapeseed plant has little competitive ability against weeds in the early growing season, which causes it to be severely damaged by weed interference. Since the long-term presence of weeds in rapeseed could reduce its quality and yield, early weed control is essential to achieve economically acceptable yields.Materials and MethodsIn order to control broadleaf weeds in rapeseed fields, a factorial experiment based on a randomized complete block design with three replications was conducted in winter 2019 in Benvar Nazer region, Andimeshk county, Iran. The experimental factors included two types of rapeseed hybrids (Hayola 50 and Agamax) and clopyralid herbicide (1.5 L ha-1 recommended dose, EC30%, Aryashimi, Iran) application with a fixed dose of 1 lit ha-1 for all treatments along with oxadiazon herbicide (recommended dose of 3 L ha-1 for using in rice as pre-plant before the two leaved barnyard grass, EC12%, Shimagro company, Iran) at doses of 100, 175, and 200 ml ha-1, and oxadiargyl herbicide (recommended dose of 3-3.5 L ha-1 for using in rice as pre-emergence or at the beginning of weed emergence in transplanted rice, SC3%, Herbicide Production Company, Iran) with doses of 100, 125, and 150 ml ha-1. Weedy and weeding control (complete control by manual weeding) were considered as control treatments. Herbicides were applied by a 12 liter back sprayer equipped with a TJET 11003 nozzle, which was calibrated for spraying 200 liters per hectare, in the initial 2-leaf stage to the beginning of 4 true leaves for chemical control of weeds in the plots. The grass weeds were removed by hand. Broadleaf weeds were counted separately according to the weed species at before spraying, three and six weeks after spraying and were cut at the soil surface and dried at 70 °C in oven. Then, weed dry weight was measured with a digital scale 0.01 and the percentage reduction in density and dry weight of weeds were calculated. In addition, the amount herbicides used on rapeseed was visually assessed using the EWRS standard table. Then, yield and yield components of rapeseed including number of siliques, seed no. per silique, 1000-seed weight, seed yield, biological yield and harvest index were measured.Results and DiscussionResults showed that the predominant weed species in the experimental plots included wild clover, queen anne᾿s lace, mallow, Anagalis spp., wild mustard, and field bindweed, which the highest frequency (31.29%) belonged to wild clover and the lowest frequency (1.03%) belonged to field bindweed. The ANOVA results showed that the reduction percentage of density and dry weight of weeds and seed yield were affected by experimental treatments; as the treatments of clopyralid + oxadiazon 100, clopyralid + oxadiazon 175, clopyralid + oxadiargyl 125 in Hyola50 hybrid and clopyralid + oxadiazon 175 in Agamax hybrid reduced the density and dry weight of weeds by 100%. While, the lowest reduction percentage of weed density and dry weight (44.74 and 55.33%, respectively) was observed in Agamax hybrid and clopyralid (1 L ha-1) treatment. Also, the highest and lowest herbicide injury on weeds were observed in clopyralid+oxadiazon 100 (9.67%) and clopyralid alone and combination of clopyralid+oxadiargyl 100 and 150 in Agamax hybrid (0%), respectively. The highest seed yield, biological yield and 1000-seed weight of rapeseed were observed in clopyralid+oxadiazon 200, oxadiargyl 125 and 150 (3377.6 kg ha-1, 11295 kg ha-1, and 3.27 g, respectively), and the lowest was observed in weedy control treatment (2064.2 Kg ha-1, 7458 Kg ha-1 and 2.87 g). 1000-seed weight is less affected by treatments and is a genetic trait. The highest and lowest number of seeds per silique under the influence of herbicide treatment were related to clopyralid+oxadiazone 175 and clopyralid+oxadiargyl 100 (23.33 and 18.17), respectively. An increase in the number of seeds per silique was observed with increasing the dose of herbicide oxadiazone in combination with clopyralid up to 175 ml ha-1. The highest number of siliques per plant was obtained in weeding treatment in Agamax hybrid with 189.33 silique per plant, which was significantly different from weedy control treatment. Also, the lowest number of weed control silique was obtained with Hayola 50 hybrid, which was not significantly different from clopyralid+oxadiazone 100 in Agamax hybrid.ConclusionAccording to the results, mixing herbicides is a solution to eliminate the competition of weeds with rapeseed and increase the yield so that the yield of up to 3.3 tons is obtained, which compared to clopyralide only as a control treatment. In general, the highest yield of rapeseed from plots treated with clopyralid+oxadiazon 200, oxadiargyl 125, and 150 were the best treatment in comparison with the applied treatments. The best treatment is the one in which rapeseed yield has been the highest. In addition, since clopyralid is a selective herbicide in rapeseed, it did not have sufficient efficacy due to poor control of important weeds such as wild mustard. It should also be noted that further testing of the above herbicide mixtures on rapeseed fields throughout the country is necessary in order to obtain the results that are the basis for recommending these mixtures in rapeseed.

Keywords

• rapeseed hybrid
• weed density and dry weight reduction
• yield