ABSTRACT Soybean cultivation requires herbicide application in the off-season, before emergence for weed desiccation, and after emergence. It is believed that the use of preand post-emergent herbicides combined with preharvest application may negatively affect the quality of soybean seeds. As such, the present study aimed to assess the effect of preand post-emergent herbicides on soybean seed quality. Five field experiments were conducted during the 2018/2019 and 2019/2020 growing seasons to investigate the effects of synthetic auxins and pre-emergents, acetyl-CoA carboxylase (ACCase) inhibitors, broadleaf herbicides, and s-metolachlor or clomazone on the quality of soybean seeds. Dicamba application combined with the pre-emergent herbicides imazethapyr/flumioxazin before soybean planting reduced seed vigor and germination. ACCase inhibitors in association with broadleaf herbicides before planting had no effect on seed quality. Applying s-metolachlor (up to 2,880 g of active ingredient [ai] ha-1) or clomazone (up to 1,800 g ai ha-1) was safe for seed germination, even when used after soybean emergence.

RESUMO No cultivo da soja, faz-se necessário a aplicação de herbicidas na entressafra, com a associação de herbicidas para a dessecação das plantas-daninhas com pré-emergentes, bem como com aplicações em pós-emergência da soja. Acredita-se que herbicidas aplicados na dessecação pré-semeadura soja, em associação com herbicidas pré-emergentes, bem como herbicidas pré-emergentes aplicados em pós-emergência da soja, possam afetar negativamente a qualidade de sementes da cultura. Assim, objetivouse com este estudo avaliar o efeito de herbicidas, aplicados em pré ou pós-emergência da soja, na qualidade de sementes produzidas. Foram conduzidos cinco experimentos no campo, durante as safras 2018/2019 e 2019/2020. Foram investigados os efeitos de auxinas sintéticas e pré-emergentes, inibidores da ACCase e latifolicidas, e smetolachlor ou clomazone sobre a qualidade de sementes produzidas. A aplicação de dicamba em associações com os herbicidas préemergentes imazethapyr/flumioxazin, em pré-semeadura da soja, diminuiu o vigor e germinação das sementes. A aplicação de herbicidas inibidores da ACCase em associação com latifolicidas, em pré-semeadura, não teve impacto sobre a qualidade das sementes. A aplicação de s-metolachlor (até 2.880 g de ingrediente ativo [ia] ha-1) ou de clomazone (até 1.800 g ia ha-1) foi segura para a germinação das sementes, mesmo para a aplicação em pós-emergência da cultura.

ABSTRACT Glufosinate and diquat may have different levels of efficacy in the pre-harvest desiccation of soybean (Glycine max (L.) Merr.) plants, and may affect quality of seeds differently, depending on the phenological stage at which they are applied. The objective of this study was to evaluate desiccation with glufosinate and diquat at the phenological stages R6, R7.1, R7.2, and R7.3, and to examine their effects on yield and quality of soybean seeds. The experiment was conducted at two sites in the state of Paraná (PR), Brazil, in the 2020-2021 crop season. A randomized block design was used, treatment groups consisted of application of glufosinate or diquat at R6, R7.1, R7.2, and R7.3, and the control group (without desiccant application). Defoliation, maturity, moisture, yield, and seed quality (vigor and germination) were evaluated. Glufosinate and diquat were effective at desiccation and had a significant effect on defoliation and maturity, with final values ≥ 98.8% and ≥ 99.3% respectively. Treatments can accelerate harvest maturity by approximately 3 d and earlier applications do not necessarily favor this acceleration, most notably in trial 1. However, desiccation at earlier stages reduced seed yield and negatively affected seed quality, with values of only 61.3% and 71.8% of vigor and germination in some situations. The application of glufosinate or diquat was effective in the pre-harvest desiccation of soybean plants, with no differences between the assessed herbicides or phenological stages. The application of glufosinate starting at R7.2 or diquat at R7.3 is ideal to avoid deleterious effects on seed yield. Applications at earlier stages may lead to losses of more than 30% seed yield. The use of diquat or glufosinate before R7.2 may reduce the quality of seeds.

Abstract Background Paraquat is a broad spectrum herbicide used particularly in burndown, in pre-plant of row crops and in the pre-harvest desiccation of some crops. In Brazil, paraquat was re-evaluated by Anvisa, leading to a prohibition of production and sales on September 22, 2020, and used until July 31, 2021. Objective The objective of this review is to characterize the use of paraquat in Brazil and describe the status in other countries, particularly the agronomic implications of its ban, possible replacements, and scenarios. Review The use of paraquat is important for weed management in different production systems. Owing to its toxicity, its use has been re-evaluated in several countries. For pre-harvest desiccation of soybeans, diquat, glufosinate, and some combinations with Protox inhibitors are highlighted as alternatives to paraquat. For pre-harvest desiccation of common beans, diquat, saflufenacil, and glufosinate could be used; however, only glufosinate could be used for wheat. For managing broadleaves weeds, glufosinate, saflufenacil, carfentrazone, and diquat are effective alternatives. Diquat may be less effective in controlling Conyza spp. resistant to paraquat. For grasses control, glufosinate, in addition to ACCase inhibitors and possible mixtures, may be helpful. Although pre-emergent herbicides are not classified as desiccant herbicides, they contribute to weed management. The adoption of herbicide-tolerant crops, mechanical control, and cover crops can be added as agricultural practices for integrated weed management. Conclusions Due to the ban on paraquat, challenges arise, and the most often suggested replacements are glufosinate, diquat, and Protox inhibitors; however, grass control will be of greater concern.

Abstract Background In the last two decades, herbicide-resistant biotypes of Conyza bonariensis, Conyza canadensis, and Conyza sumatrensis were identified. Objective: To evaluate herbicide alternatives for the control of C. sumatrensis to replace simplified management at soybean pre-sowing in the no-till system and assess the potential herbicide injury to soybeans. Methods Four experiments were conducted in Palotina, PR, to evaluate alternative managements to the herbicides commonly used in C. sumatrensis , such as synthetic auxins, pre-emergent, and burndown herbicides. All consisted of applications in pre-sowing of soybeans and weed control evaluation. Experiments I and II included evaluations during the crop, such as injury and soybean yield. In all experiments, a randomized block design was used, with four repetitions. Results The treatments with sequential applications were more effective in controlling C. sumatrensis . Triclopyr and dicamba were more effective than 2,4-D. Conclusions Dicamba was the most effective synthetic auxins when applied only with glyphosate, without sequential. With sequential glufosinate, dicamba, and triclopyr application showed the highest efficacy. Glufosinate showed better control when applied sequentially compared to saflufenacil. Pre-emergent herbicides were effective only if combined with dicamba in the first application or with sequential glufosinate. Pre-emergent, synthetic auxins, and burndown herbicides were shown to be potentially selective for soybeans.