**5. Economic impacts of herbicide resistance**

The economic impact of herbicide resistance management is related to the need to use alternative herbicides with different modes of action, yield losses caused by competition, but mainly to the weed species resistant to being controlled [25]. The cost of alternative herbicides varies according to the choice of farmer, as there is often more than one herbicide option available. Yield losses caused by competition vary according to weed and crop competitive ability, number of plants per area, vegetative stage of crops and weeds, soil fertility, and water availability, among other factors. Therefore, estimating the real economic impact of herbicide resistance on Brazilian agricultural activity is difficult.

Embrapa's Herbology Research Group (GherbE) has been continuously monitoring herbicide-resistant weeds in grain production systems in Brazil since 2010, through questionnaires and consultations with technical assistance, farmers, and other researchers; seed collection from areas suspected of resistance with subsequent tests for resistance in a greenhouse; field experiments; and visits to areas with suspected resistance. Resistance monitoring by GherbE researchers was made possible through the joint implementation of the projects "Identification and characterization of glyphosate resistant weeds in Brazil" and "Integrated management of herbicide resistant weeds in soybean production systems" [99]. Relevant information is now available showing the potential economic impact of glyphosate resistant weeds on soybean production and the most representative results are summarized here [25, 99, 100].

The average cost of nonresistant weed control in 2017, restricted to two postemergence glyphosate applications and one for desiccation, was estimated in R\$ 120.00 ha<sup>−</sup><sup>1</sup> . In a scenario of glyphosate resistant *L. multiflorum* infestation, in addition to glyphosate, it is necessary to add a graminicide (ACCase inhibitor), increasing the average cost to R\$ 177.65 ha<sup>−</sup><sup>1</sup> . If the infestation is of *Conyza* sp., the use of a latifolicide such as 2,4-D increases the average cost to R\$ 170.50 ha<sup>−</sup><sup>1</sup> . In areas infested with *D. insularis*, a weed more difficult to control than *L. multiflorum*, requires the use of graminicides in both postemergence and desiccation, and may be interspersed with contact herbicides such as paraquat and glufosinate, increasing the average management cost of this species up to R\$ 318.35 ha<sup>−</sup><sup>1</sup> . However, in mixed infestation scenarios, herbicide resistance management is complicated because herbicide options are reduced. For example, infestations of *Conyza* sp. and *L. multiflorum* require selective herbicides for cultivation during soybean vegetative phase, with flumioxazin and trifluralin being the main options, while for desiccation 2,4-D and paraquat are required for control of *Conyza* sp. and *L. multiflorum*, respectively. The average control cost in this scenario may reach R\$ 197.55 ha<sup>−</sup><sup>1</sup> . If the infestation is of *Conyza* sp. and *D. insularis*, the control cost can be up to R\$ 386.65 ha<sup>−</sup><sup>1</sup> , i.e., R\$ 266.65 ha<sup>−</sup><sup>1</sup> more expensive compared to one scenario without resistance. These estimates do not consider the possible occurrence of multiple resistance of *L. multiflorum* and *D. insularis* to graminicides or *Conyza* sp.

to latifolicides, scenarios in which the cost of management is more expensive and restricted in relation to the alternative herbicide options available [25].

According to GherbE monitoring, 59% of soybean area (20.1 out of 34.0 million ha) had infestations of glyphosate-resistant populations of *Conyza* sp., *D. insularis* and/ or *L. multiflorum* in 2017. *Lolium multiflorum* affected 4.2 million ha in the southern states, and this weed occurred simultaneously with *Conyza* sp. in 3.4 million ha*.* The areas infested by *Conyza* sp. and *D. insularis* were estimated at 7.7 and 8.2 million ha, respectively, of which 2.7 million ha correspond to mixed infestations of these two species [100]. On the GherbE website it can visualize distribution maps of these weeds in the different agricultural regions of Brazil [99]. Analyzing the infested area and the control cost according to the infesting weed species, the average cost of resistance management was R\$ 4,918,820,000.00 in 2017 [25]. If a conservative 5% yield loss by weed competition is added, the total cost of herbicide resistance in Brazil exceeds R\$ 9 billion annually in soybean cultivation alone [25].

### **6. Future trends, challenges, and conclusions**

Brazil is a consolidated agricultural power; however, the large size of its agricultural activity, especially the intensive production, makes it highly dependent on pesticides for the management of phytosanitary issues, which has led to the emergence of pests resistant to these products.

Much of the Brazilian agricultural activity (68.4%) is focused on the production of grains (52.5% soybean, 10.6% maize, and 5.3% other grains) by cultivating herbicide-resistant crop varieties. The introduction, rapid adoption, and high dependence on these technologies and their associated herbicides (58% of the national pesticide market) caused major changes in weed management practices, contributing to the selection of herbicide resistance weeds.

Today, herbicide resistance is a fait accompli in Brazil; however, the problem is not rooted in the cultivation of herbicide resistant crops but in the inappropriate use of these technologies as a whole, mainly related to off-season applications and herbicide overdose. Clearly, weed management practices must be constantly changed to prevent or delay the emergence of resistant plants in an area. However, the high specialization of farmers to grow, manage and market one or few crops with similar agricultural tasks limits the implementation of alternatives weed management measures as well as reduce more complex crop rotations (i.e., grains by vegetables instead of grains by grains), since transferring their production system to other crops requires investments in professional training, infrastructure, new agricultural implements as well as in the creation of new marketing networks; otherwise, farmers have no guaranteed economic return. In addition, farmers prefer to continue living with the herbicide resistance, and they are reluctant to adopt integrated weed management measures or new herbicide resistant crop technologies for herbicide resistance control if their profit margins are not severely compromised.

The management of the herbicide resistance may represent an increase ranging from 100 to 350% ha<sup>−</sup><sup>1</sup> of the costs devoted for weed control in relation to fields with no resistance. However, the dimensions of this phytosanitary issue is incalculable, as five glyphosate resistant weeds (*C. bonariensis, C. canadensis, C. sumatrensis, D. insularis*, and *L. multiflorum*), occurring only in soybean, infested ≥25% of the total planted area (20.1 out of 77.8 million ha) of Brazil, and caused R\$ 9 billion of losses in 2017. To know the true economic impact of herbicide resistance, the areas of other crops infested by these glyphosate resistant weeds, as well as areas affected by the other 46 cases of herbicide resistance (species x herbicide x crop situation) reported in Brazil should also be considered.

**169**

**Author details**

São Carlos, Brazil

Ricardo Alcántara-de la Cruz1

grants: 2018/15910-6 and 2019/15527-0).

large-scale implementation.

**Acknowledgements**

Leonardo Bianco de Carvalho3

UNESP), Jaboticabal, Brazil

\*, Guilherme Moraes de Oliveira<sup>2</sup>

1 Department of Chemistry, Federal University of São Carlos, São Carlos, Brazil

3 School of Agricultural and Veterinary Sciences, São Paulo State University (FCAV/

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

2 Center of Biological and Health Sciences, Federal University of São Carlos,

\*Address all correspondence to: ricardo.cruz@ufscar.br

provided the original work is properly cited.

,

and Maria Fátima das Graças Fernandes da Silva1

*Herbicide Resistance in Brazil: Status, Impacts, and Future Challenges*

Brazilian technical and scientific community specialized on weed science continually made great efforts to prevent, monitor, identify as well as discuss and establish new weed-resistant weed management strategies. However, in most cases, herbicide resistance has been fought in an inverted way, i.e., it has been tested/ implemented for solutions to the problem without determining the cause; therefore, if little effort continues to be devoted to characterize the resistance mechanism involved in each case of herbicide resistance before implementing weed management strategies, new occurrences of herbicide resistance weeds, mainly with crossand multiple-resistance, will continue to appear in the coming years in Brazil. Besides inherent biological factors of weeds to select herbicide resistance, agronomic, economic and scientific-technical factors have, directly or indirectly, contributed to increasing cases of herbicide resistance. These factors are generally linked to each other but they often are analyzed separately. Therefore, in order to achieve sustainable weed management, future studies aimed at addressing herbicide resistance problems by evaluating different weed management programs should consider these factors, as well as practical and economic aspects for their

The Brazilian weed science community have the great challenge of demonstrate to farmers that the implementation of integrated weed management programs may be expensive initially, but in the long term it is profitable and environmentally sustainable.

RAC, GMO, and MFGFS thank the "Fundação de Amparo à Pesquisa do Estado de São Paulo—FAPESP" for the financial support (main-grant: 2014/50918-7, sub-

*DOI: http://dx.doi.org/10.5772/intechopen.91236*

#### *Herbicide Resistance in Brazil: Status, Impacts, and Future Challenges DOI: http://dx.doi.org/10.5772/intechopen.91236*

Brazilian technical and scientific community specialized on weed science continually made great efforts to prevent, monitor, identify as well as discuss and establish new weed-resistant weed management strategies. However, in most cases, herbicide resistance has been fought in an inverted way, i.e., it has been tested/ implemented for solutions to the problem without determining the cause; therefore, if little effort continues to be devoted to characterize the resistance mechanism involved in each case of herbicide resistance before implementing weed management strategies, new occurrences of herbicide resistance weeds, mainly with crossand multiple-resistance, will continue to appear in the coming years in Brazil.

Besides inherent biological factors of weeds to select herbicide resistance, agronomic, economic and scientific-technical factors have, directly or indirectly, contributed to increasing cases of herbicide resistance. These factors are generally linked to each other but they often are analyzed separately. Therefore, in order to achieve sustainable weed management, future studies aimed at addressing herbicide resistance problems by evaluating different weed management programs should consider these factors, as well as practical and economic aspects for their large-scale implementation.

The Brazilian weed science community have the great challenge of demonstrate to farmers that the implementation of integrated weed management programs may be expensive initially, but in the long term it is profitable and environmentally sustainable.
