&lt;b&gt;Phytosociology of weed in the southwestern Goiás region

Weverton Ferreira Santos,Marcelo Ferreira Fernandes,Alessandro Guerra Da Silva,Eduardo Ribeiro Dos Santos,Sérgio De Oliveira Procópio

doi:10.4025/actasciagron.v40i1.33049

Abstract

Roundup Ready® technology adoption and the cultivation of a second crop have changed chemical control methods and weed management in the southwest region of Goiás State, Brazil. Considering these changes, this study aimed to perform a phytosociological survey in areas with glyphosate resistant soybeans and conventional soybeans as the main harvest and sorghum, maize, millet or fallow in succession as the second harvest. A multivariate matrix of the floristic composition was constructed, and the indicator values of the individual number and dry biomass of species were measured. Based on the number of individuals, the species Chamaesyce hirta, Bidens subalternans, and Cissampelos ovolifolia were typical of areas cultivated with glyphosate-resistant soybean, while Euphorbia heterophyla presented indicator values of areas with conventional soybean cultivation. During the second harvest period, significant indicator values were observed for Crotalaria spectabilis in maize areas, Cenchrus echinatus in sorghum, and Commelina benghalensis, Sida glaziovii, Ipomoea grandifolia, Sida rhombifolia, and Ipomoea cordifolia in areas with millet. The species Conyza bonariensis was typical in the period before the herbicide application at post-emergence in harvest. Volunteer soybean presented as typical for the period before the herbicide application at post-emergence in the second harvest. Weeds that were difficult to control or were tolerant and resistant to the herbicide applications were recorded in the areas studied.

Highlights

Soybean varieties genetically modified for resistance to glyphosate have been available for Brazilian agriculture since 2005
Phytosociological surveys were conducted in seven production systems with five repetitions at different properties, which had at least three consecutive years of implementation, totalling thirty-five agricultural areas (Table 1). These properties use predominantly the soybean cultivar modified for resistance to glyphosate with Roundup Ready technology (RR soybean) and conventional soybean as the main crop, with successions of maize, sorghum and millet or fallow in the second crop
In the comparative data of the number of individuals between soybeans genetically modified for resistance to glyphosate and conventional soybeans, the C. hirta species presented a significant indicator value (VI: 49, p: 0.01) as a typical occurrence in areas cultivated with RR soybean (Table 3)

Summary

Introduction

Soybean varieties genetically modified for resistance to glyphosate have been available for Brazilian agriculture since 2005. These cultivars have been developed to increase productivity and resistance to various factors, such as use of herbicides, diseases and lodging. The use of these cultivars has changed chemical control methods and the management of spontaneous plant communities in different farming systems With the use of Roundup Ready® technology, chemical control mechanisms have a unique action mechanism from glyphosate, which directly influences the establishment of weed plants. This herbicide has a wide action spectrum with. In less than a decade, this technology's efficiency has been endangered by the occurrence of weed species that are tolerant and/or resistant to applications of this herbicide (Webster & Sosnoskie, 2010)

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