BACKGROUNDTransgenic event DAS44406‐6 (E3) makes soybeans that are herbicide [glyphosate (Gly), 2,4‐dichlorophenoxyacetic acid (2,4‐D) and glufosinate] and caterpillar resistant. The E3 soybean was commercially released for the 2021/2022 harvest in Brazil. We conducted this study to test whether Gly and 2,4‐D applied alone and in a commercial mixture affect Asian soybean rust (ASR). Assays were conducted in detached leaves and in vivo, in a controlled environment using the herbicides Gly, 2,4‐D and Gly + 2,4‐D, and pathogen inoculation. Disease severity and spore production were evaluated.RESULTSOnly the herbicides Gly and Gly + 2,4‐D inhibited ASR in detached leaves and in vivo. When applied preventively and curatively in vivo, these herbicides reduced the disease severity and spore production of the fungus. In vivo, inhibition of disease severity reached 87% for Gly + 2,4‐D and 42% for Gly. A synergistic effect was observed with the commercial Gly + 2,4‐D mixture. Application of 2,4‐D alone in the in vivo assays did not reduce or increase disease severity. Gly and Gly + 2,4‐D act residually in inhibiting the disease. Growing E3 soybeans may combine weed and caterpillar management benefits with ASR inhibition.CONCLUSIONApplication of Gly and Gly + 2,4‐D herbicides in resistant E3 soybean shows inhibitory activity for ASR. © 2023 Society of Chemical Industry.

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Brazil southern region edaphoclimatic conditions allow farmers to grow perennial winter legumes. However, at summer, a seasonality occurs in the production of these species allowing the grown of annual crops such as corn. In this way, interference between white clover (Trifolium repens L.) living mulch and corn crop (Zea mays L.) was studied using a clover sward established after one and two growing season in relation to the usual system of corn grown over black oat straw aiming to study the relationships occurring in this intercrop, such as white clover herbicide suppression, competition and its nitrogen effects on corn yield as well as its potential to became perennial after corn harvest. White clover suppression management was established in the main plots and corn nitrogen fertilization (0, 60, 120, 180 kg ha-1) was performed in the subplots (4.2 × 8 m) in a randomized block design with four replications. White clover suppression managements were: (i) partial suppression achieved by mowing the plots at the corn seeding day; (ii) partial suppression achieved by mowing plus chemically broadcast application of 2.4-D; (iii) partial suppression achieved by a chemically broadcast application of glyphosate. Corn grain yields ranged from 3.0 to 12.2 Mg ha-1. Nitrogen input and herbicide management are important elements to reduce white clover competition and increase corn yield. It is possible to manage white clover as living mulch in corn with its full recovery after corn harvest without replanting. Clover with 1 cycle is easier suppressed than perennial clover sward and can be handled in intercropping with corn without affecting grain yield, with ability to resume growth in the next growing season.

Residual herbicides and cover crops are important tools inside an integrated weed management program. The straw produced in crop rotation can interacts with herbicides. The aim of this study was to evaluate the interaction of diclosulam, sulfentrazone, imazethapyr, flumioxazin, s-metolachlor and pyroxasulfone with black oat, cereal rye, common vetch and oilseed radish cover crops and it´s reflection on weed control and soybean production. Were evaluated the biomass production of cover crops and its influence on the soybean population. A phytosociological survey of the weed community was carried out, further evaluating the control provided by the herbicides and its effects on soybean productivity. Diclosulam was the more efficient herbicide tested, reducing both weed density and biomass (68% and 89%, respectively) compared to the fallow, independently of cover crop straw. The best control levels for the population identified were provided by the combination of the herbicides diclosulam with black oat, radish or fallow. We observed that herbicide efficacy in this case was more related with control spectrum than with herbicide-straw interation. This research demonstrates that the integration of cover crops and residual herbicides is efficient in the suppression and control of weeds in the soybean crop in the no-tillage system.

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