**1. Introduction**

The domestication of plants over a long time came with several challenges to maintain their sustainability. It is known that cultivated crops would suffer attacks from pests and diseases, causing great yield losses with the ever-present possibility of hunger for the population, mainly due to the lack of resources and knowledge. Even today with advances in technologies to control invaders, food losses due to pests and diseases range from 10 to 90%, with an average of 35–40%, for all potential crops of food and fiber [1]. Pesticides are chemical products that contribute to agricultural production processes, mainly large scale, as agents of chemical, physical, and biological processes [2]. In the south of Brazil, the monoculture of soybeans, wheat, and rice was associated with the mandatory use of pesticides for those who intended to use government rural credit. Today, pesticides are disseminated in conventional agriculture, as a short-term solution for pest and disease infestation [3].

Brazil is one of the largest agricultural producers in the world and the second country that exports these products, playing an important role in the local economy. To maintain such production, this sector intensively uses transgenic seeds and chemical inputs, such as fertilizers and pesticides. Brazil is the largest consumer of pesticides in the world, with an extensive area of planting [4]. The consumption of herbicides in Brazil was about 540,000 tons of formulated (commercial) products in 2017 [5]. Glyphosate is the most widely used pesticide in Brazil, with 173,150.75 tons of acid equivalent marketed in 2017 [6]. One of the main consequences of weed resistance to herbicides is the increase in weed control costs, which is hardly addressed in scientific publications, but of great importance for the productive sector.

Glyphosate (*N*-phosphonomethyl glycine) is a nonselective and systemic herbicide applied in postemergence, which belongs to a chemical group of replaced glycines. It presents a wide spectrum of actions, enabling the control of annual and perennial weeds with broad and narrow leaves. Due to excellent weed control along with its ease of handling, low cost, and increased productivity, glyphosate has become the most widely used herbicide in the world [7]. This herbicide is registered in Brazil for the following crops: cotton, rice, plum, banana, cocoa, coffee, sugarcane, citrus, coconut, eucalyptus, beans, tobacco, apple, papaya, corn, nectarine, pear, peach, pine, rubber tree, soybean, wheat, grape, pastures, forage ryegrass, and black oats [7]. Glyphosate acts by inhibiting the enzyme 5-enolpyruvylshikimate-3-phosphate synthase (EPSPs) and, consequently, the biosynthesis of aromatic amino acids, lignins, flavones, isoflavones, anthocyanins, and several indispensable components for the plant, leading to plant death [7].

It is of paramount importance to understand the behavior of the herbicide in the plants. Therefore, the absorption of glyphosate takes place in the aerial part of the plants, having a maximum absorption 96 h after application, translocated by simplasto with photoassimilates of the leaves for meristematic tissue reaching the target site. In water it presents a weak acid behavior and presents four variable dissociation constants (pKa between 2.6 and 10.3), in which it presents cell absorption facilitated by phosphate carriers that are in the cell membranes [8].

Glyphosate is the most widely used pesticide in the world due mainly to the large number of genetically modified crops resistant to this product [9]. However, with the increase in the number of agricultural areas with transgenic crops (glyphosateresistant), mainly soybean, cotton, and corn, together with the high use and incorrect application of this herbicide, new cases of resistant weeds appear [8]. In the world, 47 species of glyphosate-resistant weeds are already reported, and 9 of them are in Brazil [10]. **Figure 1** presents the number of weed species resistant to various herbicides of different resistance mechanisms reported worldwide.

Acetolactate synthase (ALS) inhibitor herbicides have the highest number of resistant species (162 species) (**Figure 1**). 4-Hydroxyphenylpyruvate dioxygenase (HPPD) inhibitor herbicides have the smallest number of resistant species (two species). **Figure 2** shows that the United States is the country with the most cases of unique resistance. Brazil has 51 cases of herbicide-resistant weeds already recorded.

**Figure 3** presents the amount of herbicide-resistant weed species within weed families. The family that has the most cases of herbicide resistance is the Poaceae family with 82 registered cases. The Caryophyllaceae family presents fewer cases of resistant weed species (six species).

**Figure 4** presents the amount of weed species that have simple resistance to each herbicide. Atrazine presents the largest number of weed species with simple resistance, with 66 species registered. For glyphosate there are reported 43 species of weed resistance, the second being herbicide with the highest number reported.

**5**

**Figure 2.**

**Figure 1.**

*Source: Heap [10].*

*Current Approaches to Pesticide Use and Glyphosate-Resistant Weeds in Brazilian Agriculture*

*Number of weed species resistant to various herbicides of different resistance mechanisms reported worldwide.* 

The mechanisms that generate resistance to herbicides in weeds can be separated

into the following: (i) related to the site of action (target-site resistance, TSR) and/or (ii) not related to the site of action (nontarget-site resistance, NTSR) [9]. Mutation of the gene encoding enzyme EPSPS and amplification of this gene are

*Increased cases of resistant weeds reported in various countries and Europe. Source: Heap [10].*

*DOI: http://dx.doi.org/10.5772/intechopen.91872*

*Current Approaches to Pesticide Use and Glyphosate-Resistant Weeds in Brazilian Agriculture DOI: http://dx.doi.org/10.5772/intechopen.91872*

**Figure 1.** *Number of weed species resistant to various herbicides of different resistance mechanisms reported worldwide. Source: Heap [10].*

**Figure 2.** *Increased cases of resistant weeds reported in various countries and Europe. Source: Heap [10].*

The mechanisms that generate resistance to herbicides in weeds can be separated into the following: (i) related to the site of action (target-site resistance, TSR) and/or (ii) not related to the site of action (nontarget-site resistance, NTSR) [9]. Mutation of the gene encoding enzyme EPSPS and amplification of this gene are

*Multifunctionality and Impacts of Organic and Conventional Agriculture*

Brazil is one of the largest agricultural producers in the world and the second country that exports these products, playing an important role in the local economy. To maintain such production, this sector intensively uses transgenic seeds and chemical inputs, such as fertilizers and pesticides. Brazil is the largest consumer of pesticides in the world, with an extensive area of planting [4]. The consumption of herbicides in Brazil was about 540,000 tons of formulated (commercial) products in 2017 [5]. Glyphosate is the most widely used pesticide in Brazil, with 173,150.75 tons of acid equivalent marketed in 2017 [6]. One of the main consequences of weed resistance to herbicides is the increase in weed control costs, which is hardly addressed in scientific publications, but of great importance for the produc-

Glyphosate (*N*-phosphonomethyl glycine) is a nonselective and systemic herbicide applied in postemergence, which belongs to a chemical group of replaced glycines. It presents a wide spectrum of actions, enabling the control of annual and perennial weeds with broad and narrow leaves. Due to excellent weed control along with its ease of handling, low cost, and increased productivity, glyphosate has become the most widely used herbicide in the world [7]. This herbicide is registered in Brazil for the following crops: cotton, rice, plum, banana, cocoa, coffee, sugarcane, citrus, coconut, eucalyptus, beans, tobacco, apple, papaya, corn, nectarine, pear, peach, pine, rubber tree, soybean, wheat, grape, pastures, forage ryegrass, and black oats [7]. Glyphosate acts by inhibiting the enzyme 5-enolpyruvylshikimate-3-phosphate synthase (EPSPs) and, consequently, the biosynthesis of aromatic amino acids, lignins, flavones, isoflavones, anthocyanins, and several

indispensable components for the plant, leading to plant death [7].

facilitated by phosphate carriers that are in the cell membranes [8].

herbicides of different resistance mechanisms reported worldwide.

It is of paramount importance to understand the behavior of the herbicide in the plants. Therefore, the absorption of glyphosate takes place in the aerial part of the plants, having a maximum absorption 96 h after application, translocated by simplasto with photoassimilates of the leaves for meristematic tissue reaching the target site. In water it presents a weak acid behavior and presents four variable dissociation constants (pKa between 2.6 and 10.3), in which it presents cell absorption

Glyphosate is the most widely used pesticide in the world due mainly to the large number of genetically modified crops resistant to this product [9]. However, with the increase in the number of agricultural areas with transgenic crops (glyphosateresistant), mainly soybean, cotton, and corn, together with the high use and incorrect application of this herbicide, new cases of resistant weeds appear [8]. In the world, 47 species of glyphosate-resistant weeds are already reported, and 9 of them are in Brazil [10]. **Figure 1** presents the number of weed species resistant to various

Acetolactate synthase (ALS) inhibitor herbicides have the highest number of resistant species (162 species) (**Figure 1**). 4-Hydroxyphenylpyruvate dioxygenase (HPPD) inhibitor herbicides have the smallest number of resistant species (two species). **Figure 2** shows that the United States is the country with the most cases of unique resistance. Brazil has 51 cases of herbicide-resistant weeds

**Figure 3** presents the amount of herbicide-resistant weed species within weed families. The family that has the most cases of herbicide resistance is the Poaceae family with 82 registered cases. The Caryophyllaceae family presents fewer cases of

**Figure 4** presents the amount of weed species that have simple resistance to each herbicide. Atrazine presents the largest number of weed species with simple resistance, with 66 species registered. For glyphosate there are reported 43 species of weed resistance, the second being herbicide with the highest number reported.

**4**

already recorded.

resistant weed species (six species).

tive sector.

## *Multifunctionality and Impacts of Organic and Conventional Agriculture*

#### **Figure 3.**

*Number of herbicide-resistant weed species per weed family. Source: Heap [10].*

examples of TSR mechanism, while reduced absorption, differential translocation, high metabolism, and glyphosate sequestration by the vacuoles are examples of NTSR mechanism [11]. Thus, it is necessary to know about the mechanisms of weed resistance to herbicides to perform good management practices for the prevention of the occurrence of new resistant biotypes in other areas and, mainly, for the determination of preventive management programs to the selection of resistant biotypes and also for the determination of the practices of weed control already selected [9].

The aim of the authors in this chapter was to present pesticide use and general characteristics of glyphosate- and herbicide-resistant weeds in Brazil.

**7**

**Figure 5.**

*Current Approaches to Pesticide Use and Glyphosate-Resistant Weeds in Brazilian Agriculture*

The agricultural production in Brazil plays an important role in the Brazilian economy, thanks to which this country is one of the world's leading producers of agricultural commodities. To keep up with production, this sector uses intensively transgenic seeds and chemical inputs, such as fertilizers and pesticides—chemical or biological substances used to protect crops against the introduction and spread of pests such as insects, fungi, bacteria, viruses, mites, nematodes, and weeds [4, 12]. Regarding the function of pesticides, they all have the same common action, which is to block the vital metabolic processes of the organisms in which they are toxic. Currently, the total amount of pesticide commercialized in Brazil is US\$10,522 billion per year, 14% less than 2014 (**Figure 5**), or 21% in a global market estimated to be worth US\$50 billion. In a country with a high pest index due to tropical

climate, the farmers' challenge is to reduce pesticide application (which is nowadays the main pest management), as well as to reduce the cost of production and the

Among the several alternatives for pest control in crops, the chemical method is still the most widely used, due to its practicality, efficiency, and speed. However, if pests are not controlled, they can drastically reduce the crop productivity. Among the pesticide classes, herbicides (selective and nonselective) used for weed control and also applied for crop desiccation represent 33% of consumption in the country,

Due to the high total amount of pesticides used, some agricultural crops deserve attention, not because these products are intensively applied per unit of cultivated area but because these crops occupy large areas in Brazil. Half of the pesticides commercialized in the country are used in soybean crop, followed by the main crops

Pesticide use differs in the various regions of the country, where intensive and traditional agricultural (not use chemical product intensively) activities are mixed. Located in Midwest, the Mato Grosso state is the one that uses the most pesticides (24%) in the country, and the second is São Paulo state, located in Southeast

*DOI: http://dx.doi.org/10.5772/intechopen.91872*

**2. Pesticide use in Brazilian agriculture**

associated risks to human health and natural resources.

followed by insecticides (29%) and fungicides (28%) (**Figure 6**).

such as sugarcane (12%), corn (11%), and cotton (9%) (**Figure 7**).

*Total commercialization of pesticides in Brazil from 2014 to 2018. Source: SINDIVEG [13].*

*Current Approaches to Pesticide Use and Glyphosate-Resistant Weeds in Brazilian Agriculture DOI: http://dx.doi.org/10.5772/intechopen.91872*
