The impact of using pre- and post-emergence herbicides with adjuvants in controlling weeds in canola fields Brassica napus L.

Introduction: Oilseeds are the world’s second-largest food source, surpassed only by cereals. Among them, rapeseed stands out as a globally significant oil plant. The prevalence of weeds in rapeseed has led to an increased reliance on herbicides, particularly due to their efficiency and rapid action. However, only six herbicides have been officially recommended for chemical control in Iranian rapeseed fields. Butizan Star (inhibitor of cell division + artificial auxins) pre-emergence and dual-purpose herbicide, clopyralid selective and systemic and post-emergence herbicide and auxin inhibitors and cycloxydim (Focus), haloxyfop R methyl ester (Galant Super) and colthodim (Select Super) are systemic herbicides and selective and acetyl coenzyme carboxylase inhibitors are common herbicides that have been registered to control broad and narrow leaf weeds in rapeseed fields in Iran. To expand canola cultivation in Iran, innovative weed management strategies are crucial. Herbicide mixtures offer a promising approach, potentially enhancing their efficacy and mitigating the development of herbicide resistance in weeds. This practice aims to create a more diverse usage pattern, reducing the risk of relying solely on single herbicides. To optimize herbicide effectiveness and reduce chemical costs, incorporating adjuvants is crucial for weed control. Adjuvants can enhance herbicide performance by reducing surface tension, preventing droplet runoff from leaves and ensuring better coverage. This research aims to investigate the potential of herbicide mixtures, both in pure form and with additives, to optimize weed control in rapeseed fields. The study will assess the impact of these treatments on rapeseed plants, particularly the potential for damage when herbicides are used in combination.
Materials and Methods: In order to evaluate the effectiveness of several herbicides alone and in combination with adjuvants for controlling weeds in rapeseed fields, an experiment was conducted in 2023-2024. The field was prepared using a rotary bulldozer and two perpendicular discs to break up soil clods. Seeds were planted at a depth of 2-3 cm, with approximately 10 cm spacing between plants. The experiment was performed in a factorial design based on randomized complete blocks (RCBD) with three replications in Alashtar County, Lorestan province. The treatments included the pre-emergence application of the herbicide Butisan Star, the post-emergence combination of herbicides such as Clopyralid + Haloxifop-R Methyl, Clopyralid + Clethodim, Clopyralid + Cycloxydim, and a mixture of all treatments with the adjuvants PCGate and Uni-soap, along with two control treatments: weed-free (hand weeding) and weed-infested (no control). Herbicides were applied using a rechargeable backpack sprayer (Matabi Elegance Plus model). Weed samples were collected four weeks after herbicide application using a 0.5 x 0.5 m quadrat from each plot. At the end of July, plant height, biological yield and yield components weight were measured from a 1 x 1 meter square area in each plot. To estimate final yield, a one square meter area was harvested from the center of each plot. Data analysis was performed using SAS 9.4 software. Mean comparisons were conducted using the LSD test at a significance level of 5%.
Results: The results showed that the lowest density and dry weight of Myagrum perfoliatum L., Galium aparine L., Sinapis arvensis L., Capsella bursapastoris (L.) Medik., Alopecurus myosuroides Huds. and Muscari neglectum Guss. ex Ten. were related to Butisan Star treatment with adjuvants, which almost was similar to the hand weeding treatment. The highest reduction in traits such as density and dry weight of total weeds (1.09 gr), number of pods per plant (95), maximum plant height (154 cm), thousand seed weight (4.93 gr), seed yield (4018 k.ha-1), harvest index (30.61%), and oil percentage (46%) were achieved by the application of the pre-emergence Butisan Star in combination with Uni-Soap. Post-emergence treatment with a mixture of clopyralid + cycloxydim along with the surfactant Uni-soap resulted in a high percentage of weed control and an increase in performance traits of canola compared to the control treatment.
Conclusions: The results emphasize the importance of a comprehensive approach to weed management in canola, incorporating both pre- and post-emergence treatments tailored to specific weed species. Further research is warranted to explore the long-term effects of these herbicide mixtures and the potential development of herbicide resistance. This information can guide the development of sustainable weed management strategies for optimal canola production.