Resumo em Inglês:

Abstract Glyphosate-Resistant Crops (GR crops) have caused considerable changes in weed management worldwide. In Brazil, GR cultivars of soybean and corn were officially introduced in the 2005/06 and 2011/12 crops, respectively. This technology has radically changed the weed management system, having an enormous impact on national agriculture. The objective of this review was to analyze the general aspects that led to the adoption of this technology in Brazil and present its future consequences and challenges. The adoption of GR soybean and corn was swift and comprehensive. Ten years after its introduction, GR soybean and corn are grown in most areas with these crops in Brazil. This success can be attributed to the reduction of costs, the broad spectrum of control provided by glyphosate, the solution for effective management resistance to ALS and ACCase inhibitors, the excellent managing of weeds that are difficult to control, the reduction of crop injury and carryover problems. However, the exclusive and consecutive use of glyphosate alone resulted in intense selection pressure for resistant weeds to this herbicide, which has become one of the most prominent challenges with these crops. Therefore, the future sustainability of GR soybean and corn will not be possible without the combination with other technologies, within integrated weed management.

Resumo em Inglês:

Abstract: Background: Mixtures of herbicide sites of action (SOA) are often promoted as an effective practice for proactive herbicide resistance management, but the cost of implementation is less-often considered in these recommendations, especially in the academic literature. Objective: Estimate the costs of implementing herbicide SOA mixtures that are effective for herbicide resistance management under different scenarios involving crops, weed species, and existing resistance. Methods: Using data from the Guide for Weed, Disease, and Insect Management in Nebraska, an optimization function was used to find the lowest cost for effective weed control (single herbicide providing ≥90%), and effective resistance management (at least 2 SOA providing ≥90%) under various crop, weed, and herbicide resistance scenarios. Results: In corn and soybean, effective SOA mixtures for waterhemp and Palmer amaranth increased herbicide costs at least 2-fold compared to herbicide costs that provided effective weed control with a single SOA. Resistance to certain SOA had greater impact on the cost of effective herbicide mixtures; in corn, resistance to SOA Group 5 or Group 9 herbicides caused the greatest increase in mixture costs, whereas in soybean Group 9 or Group 14 resistance caused the greatest increase in mixture costs. In dry edible bean, effective mixtures were at least 5 times more expensive than similar scenarios in soybean, and in several scenarios, there were no herbicide mixtures available that met effective resistance management criteria. Conclusions: The use of effective herbicide SOA mixtures has sound scientific basis for slowing the evolution of herbicide resistance, but the cost of implementation is a major barrier for widespread adoption even in fields where herbicide resistance is not yet present.

Resumo em Inglês:

Abstract There is a popular demand for more natural means of pest management, including weed management, as well as a demand by farmers for herbicides with new chemistries and/or new modes of action to which current weed resistances do not apply. Natural compounds offer a source compounds that can either meet these needs in their natural state or as templates for herbicides with better physicochemical properties for field use. In some cases, simply identifying a good herbicide target site with a natural phytotoxin can be valuable, even though that compound is not used as a template for new herbicides. Compared to insecticides and fungicides, natural compounds have been under-utilized for herbicides. Despite their need, living, microbial biocontrol agents have had little impact on weed management in crops, despite decades of research to discover and develop such products. Management of insect and plant pathogens with microbial biopesticides has been much more successful. The reasons for this and possible solutions are discussed. Killed microbial preparations containing potent phytotoxins avoid some of the issues with live microbes, and such products are under development. This type of product can also offer more than one new mode of action in a single preparation. Precision and smart spray systems can improve the economics of both natural product-based herbicides and microbial bioherbicides.

Resumo em Inglês:

Abstract Farming began in Australia and New Zealand after the arrival of European settlers, who brought with them many of the weeds that later infested their cropping systems. Herbicides have since become the dominant form of weed control in both countries. Early active ingredients, such as 2,4-D, were unable to control all types of weeds, sparking the development of many other herbicides with different modes of action. While most of the land in these countries is used for pasture, many crops are also grown, with an emphasis on grains, including wheat, barley, and oats, as well as horticultural crops in New Zealand such as wine grapes, kiwifruit, and apples. An overreliance on herbicide use due to their high level of effectiveness for weed control has led to the evolution of herbicide-resistant weeds, with some weed populations developing resistance to multiple herbicide modes of action. Integrated weed management practices have been adopted by many farmers to reduce the reliance on herbicides, although widespread uptake is yet to occur. These practices use non-chemical methods in combination with herbicides to deal with hard-to-control and herbicide-resistant populations, as well as reduce the risk of resistance development. In addition to resistance, other concerns surrounding herbicide use also exist, such as the impact of herbicides on human health and the environment. This review summarizes the history of herbicides in Australia and New Zealand and discusses the issues surrounding their use as well as potential future directions for sustainable weed control.

Resumo em Inglês:

Abstract Weeds pose a serious threat in achieving sustainable and profitable crop production. South Asia, as both a major food-producing and consuming region, needs a linear increase in food grain production. Among the several methods of weed management practice, herbicides are the most cost-effective and timely solution. Rice and wheat are the major staple food crops and the introduction of low-dose high efficacious herbicides, such as pyrazosulfuron-ethyl and sulfosulfuron in rice and wheat, respectively, have the major share in the region. With the continuous use of similar herbicides or application of a limited number of herbicides with a similar mode of action in intensive cropping systems, the evolution of herbicide resistance in many weeds has become a serious concern. With limited options of alternate herbicides, the evolution of cross and multiple resistance has emerged as a major challenge. This review has highlighted the usage of herbicides in South Asian countries, the development of herbicide resistance in major crops of the region, and the possible solutions. The adoption of site-specific integrated weed management in managing both herbicide resistance and weed menace, and location-specific agronomic interventions remains critical. The immense potential of adopting novel technologies, such as the use of economic sensing devices for real-time weed identification and spot-spraying, and early detection of herbicide resistance in weeds and their phenotypes, might offer alternatives of herbicide use for safer and cleaner economies.

Resumo em Inglês:

Abstract Herbicide use has deeply changed weed management and cultivation practices in France as well as round the world. However, the use of herbicides is more and more questioned, so that it appeared interesting to us to take stock of herbicide use in France. Since 1913, it has been possible to reconstruct the marketing and withdrawal of all the herbicidal active substances used in cultivated plots. Developed to compensate for the lack of manpower, chemical weed control started at the end of the 19th century with the use of mineral molecules. While copper sulfate can be considered as the first active substance with which technical experiments were carried out, sulfuric acid was the molecule that saw the greatest development because of its efficiency. The discovery of active substances in the United States and Great Britain during World War II allowed for the development of selective weed control, first for eudicotyledonous plants and then for grasses. In France, a total of 233 active substances have been authorized either alone or in combinations. Active substances have been used for more than 27 years on average, but 2,4-D and MCPA have been used continuously for more than 75 years. The effects of these molecules on the environment and health are responsible for most of the questions about their use. The withdrawal of key molecules could soon call into question the very effectiveness of weed control and perhaps put an end to an agronomic innovation that has been in use for nearly one hundred years.

Resumo em Inglês:

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.

Resumo em Inglês:

Abstract Background Agriculture in South America (SA) had a great expansion in the last decades and weed control changed accordingly with region and crop practices. Objective The objective of this review is to present the history of herbicide use and discuss the main changes in weed management in SA. Methods Herbicide use quantities were obtained from official institutions and commercial organizations in Argentina, Brazil, Chile, Paraguay and Uruguay. Data were summarized per active ingredient, herbicide mode of action or crop. The evolution of the cultivated area of the main crops in each country, and the crop and weed management associated to it were considered to discuss the importance and the consequences of the main herbicides used. Results In 2019 the most used herbicides in Brazil were glyphosate, 2,4-D, atrazine, paraquat and diuron representing 62, 15, 7, 5 and 2% of the total amount used. In Argentina, the increasing selection of herbicide resistant populations (4 cases/year), resulted in utilization of older chemistries. Weed control in Uruguay is traditionally benefited from crop/pasture rotations but recently is also facing problems of continuous cropping systems. Agriculture in Chile is more diverse, but similar patterns and problems of herbicide use are present. Conclusions Intensification of agriculture, no-tillage, glyphosate resistant crops, and herbicide resistant weeds were the most important drivers of herbicide use changes in SA. Integrated weed management is unpostponable to provide sustainable increasing food production in SA.

Resumo em Inglês:

Abstract Mixing herbicides is a common practice in agriculture, to optimize farm management practices, widen the weed control spectrum, enhance application efficiency, and manage herbicide resistance. Interactions between herbicides can occur within the spray tank, on the leaf surface, and/or inside the plant, resulting in physicochemical and physiological interactions. Additive, synergistic, or antagonistic effects can result from these interactions. Given the range in plant response and the potential for negative and positive outcomes for weed management, predicting herbicide interactions before using mixtures would be of great value. Therefore, the physiological responses in the literature can help to ensure efficient weed control and avoid unwanted effects in the field. This review compiles information on physiological and physicochemical interactions between herbicides, addressing the most known cases of synergism, antagonism, and additivity, as well as their physiological bases, and the methods for evaluating herbicide interactions. Reference models for herbicide interactions have been reported and they usually interfere interpretation of the mixture effect. Antagonistic interactions can increase the evolution of weed resistance by favoring the survival of individuals exposed to the herbicide. Physicochemical incompatibility in the spray tank usually causes herbicide antagonism, whereas both synergism and antagonism can result from increased or decreased uptake/translocation and from physiological changes in the plant.

Resumo em Inglês:

Abstract Southeast Asia’s rich natural resources and favorable climatic conditions make it conducive for intensive rice-based, corn-based and perennial crops-based cropping systems. Regardless of the cropping system, weeds remain to be among the major factors that limit yields. The use of herbicides to manage weeds in these systems has been increasing through the years. The use of 2,4-D started in the late 1940s and remains as a major herbicide to control rice weeds. The 1980s saw the introduction of multiple active ingredients of herbicides for rice, corn and perennial crops, mostly selective herbicides with highly specific target sites and MOA. Glyphosate, commonly used in perennial crop-based systems, is now used at pre-planting in rice and corn and post-emergence in genetically modified corn. The intensive and continuous use of herbicides resulted in resistance development in weeds. To date, 37 unique cases of herbicide resistance are reported involving 17 weed species and 30 active ingredients. The rise in herbicide resistance and environmental pollution is largely due to insufficient farmer education on proper use of herbicides and integrated weed management, poor product stewardship, and lax implementation of pesticide policies and regulations. A sustainable weed management approach that embraces integrated and precise weed management is needed. We propose a sustainable weed management framework involving the various stakeholders to strengthen partnership, improve implementation and formulation of fair policies and regulations for the industry, increase investment in research and development of appropriate weed control technologies, and educate farmers, industry players and the general public.

Resumo em Inglês:

Abstract RNA interference (RNAi) is a next-generation technology for weed management. Weeds would be sprayed with small RNAs (sRNAs) capable of inducing gene silencing (referred to as spray-induced gene silencing, SIGS) without involving the use of transgenes, reaching traditional targets in chemical control, targets that are not today more sensitive to herbicides and even new targets. Here we present the main challenges and opportunities for using SIGS as a practical tool for weed management. The development of SIGS in weed science has been slower compared to other crop protection areas such as entomology and plant pathology due to the difficulty of obtaining stable molecules that easily enter the plant, without off-target risks to crops, and that in small amounts guarantee systemic silencing with effectiveness. To overcome the challenges, it is necessary to achieve the synthesis of sRNAs on a large scale, making the field application practical and economical, develop formulations that protect sRNAs inside and outside the plant, and substantially increase the genomic and transcriptomic information available for weeds. Once these barriers have been overcome, SIGS technology could be similarly used in the field as herbicides are used today, spraying directly on the crop and selectively controlling weeds. This will provide a new tool for weed management, herbicide resistance management, and potentially exploration of new plant enzyme targets never before achieved by chemical control.

Resumo em Inglês:

Abstract Nowadays only five global corporations operate herbicide discovery programs. In response to this industry consolidation, few new herbicide discoveries and global evolution of herbicide resistant weed populations there has been the very recent emergence of currently nineteen small start-up companies focused on herbicide discovery. This diversity and focus in start-ups is hoped to result in innovative new herbicide discovery that is needed to counter major herbicide resistance evolution in global weed species.