Among biological factors, weeds are the most important limiting factor for crop yields, as well as increasing production costs. The aim was to determine the influence of control and coexistence of weed community on soybean crop yield and to define the period before interference, the critical period of interference prevention and the total period of interference prevention, with the comparative use of chemical and mechanical methods for weed eradication. The study was conducted in an experimental field in the 2018/2019 harvest. A randomized block with four replications was implemented as experimental design, using two methods for control. The evaluated periods were 0-10, 0-20, 0-30, 0-40, 0-50, 0-60 and 130 days after crop emergence. It was possible to observe that the use of the chemical method generated a higher yield compared to mechanical method. The period before the interference in both chemical and mechanical management was similar, approaching 20 days after crop emergence. The critical period of interference prevention was between 20-50 and 40.5 days after crop emergence in chemical and mechanical methods, respectively. The total period of interference prevention was extended to 50 and 40.5 days after crop emergence in chemical and mechanical methods, respectively. The reduction in productivity due to weed interference was 1639 kg ha-1 (55%)and 947 kg ha-1 (34.6%) in chemical and mechanical methods, respectively.

management strategies in a long-term crop rotation system. Adv Weed Sci. 2023;41:e020220053.

management strategies in a long-term crop rotation system. Adv Weed Sci.2022;40:e020220053.

Palmer amaranth (Amaranthus palmeri S. Watson) is a troublesome weed in several cropping systems in the US. The evolution of resistance to multiple herbicides is a challenge for the management of this weed. Recently, we reported metabolic resistance to 2,4-D mediated by cytochrome P450 activity in a 6-way-resistant A. palmeri population (KCTR). Plant growth temperature can influence the herbicide efficacy and level of resistance. The effect of temperature on 2,4-D resistance in A. palmeri is unknown. In this research, we investigated the response of KCTR and a known susceptible (MSS) A. palmeri response to 2,4-D grown at low- (LT, 24/14°C, d/n) or high (HT, 34/24°C, d/n) temperature regimes. When MSS and KCTR plants were 8-10 cm tall, they were treated with 0, 140, 280, 560 (field recommended dose), 1120, and 2,240 g ai ha-1 of 2,4-D. Further, 8-10 cm tall MSS and KCTR plants grown at LT and HT, were also treated with [14C] 2,4-D to assess the metabolism of 2,4-D at LT and HT. The results of dose-response experiments suggest that KCTR A. palmeri exhibits 23 times more resistance to 2,4-D at HT than MSS. Nonetheless, at LT, the resistance to 2,4-D in KCTR was only 2-fold higher than MSS. Importantly, at HT there was enhanced metabolism of 2,4-D in both KCTR and MSS A. palmeri, than at LT. Further, treatment with cytochrome P450- inhibitor, malathion followed by 2,4-D increased the susceptibility of KCTR at HT. Overall, rapid metabolism of 2,4-D increased KCTR resistance to 2,4-D at HT compared to LT. Therefore, the application of 2,4-D when temperatures are cooler can improve control of 2,4-D-resistant A. palmeri.

Crop management and herbicide rotation have influenced the sustainability of production systems. The cover crops use and pre-and post-emergence herbicides are important tools that help farmers’ strategies and conserve the agricultural system. In this context, the objective of this research was to evaluate the dry matter production of different cover crops before the establishment of corn, the effect on decreasing weed population, and the increase in corn yield. In addition, the influence of pre-and post-emergence herbicides on summer cultivation, observing the behavior concerning weeds, crop injury, and crop yield. The experiment was conducted during the years 2018-2019 in Sertão/RS - Brazil. The experimental arrangement was of randomized blocks with four replications. The treatments used were three different winter cover crops preceding corn cultivation × four preemergence herbicides × four post-emergence herbicides, totaling 192 experimental units. Going through the results, atrazine and atrazine + simazine used in pre-emergence had more influence on weed number reduction, and the post-emergence ammonium glufosinate herbicide promoted the highest weed control in post-emergence. Amicarbazone and glyphosate resulted in the best combination for corn yield using in pre-and post-emergence, respectively. Rye + turnip + vetch as cover crop resulted in higher biomass production, more significant weed number reduction, and increase corn yield.

Wheat is the most important income-generating crop in southern Brazil during the cold season. It also contributes to the crop rotation system and increases the yield of successive crops. During its growth cycle, herbicides are used to control weeds, which are the main factor limiting wheat productivity. Further, high costs of weed control directly affect crop economic returns. The objective of this study was to evaluate the effect of the application of two herbicides, namely, 2,4-D and iodosulfuron-methyl, on the productivity of two wheat cultivars during the nine different stages of crop development. The most suitable crop stage for herbicide application, as described in the corresponding label on the package, is at the beginning of tillering. 2,4-D had a significant impact on productivity parameters, reducing the number of tillers, the number of ears, and the number of tillers without grains, while increasing the number of tillers without ears and ears without grains, indicating greater phytotoxicity and, ultimately, reducing crop productivity. Conversely, iodosulfuron-methyl showed greater selectivity to the wheat cultivars tested and caused a much lesser impact on the productivity parameters measured.