Weeds in Second Corn Crops in the Period of Transgenic Soybean Implantation in the Middle Paranapanema Region

A.C.S Hirata,A.P Duarte,R.C.R.M Duarte

doi:10.1590/s0100-83582018360100139

Abstract

ABSTRACT: The Middle Paranapanema region concentrates a large part of the second corn production in São Paulo State. Weed surveys in commercial areas are important for monitoring and directing their management. In 2006, 2007, and 2008, weed surveys were carried out on 27, 25, and 24 corn crops, respectively, in ten counties of this region. At the grain filling stage, crops were zigzag sampled with 20 points of 1 m2 per area. In addition, information on weed management, soil cover, and history of the summer crop were collected. The phytosociological parameters frequency, density, abundance, and importance value index were determined. The results evidenced Cenchrus echinathus as the most important species in 2006 and 2007, in addition to high importance values in 2008, which reflected the need to improve its management. Bidens pilosa, Digitaria horizontalis, and Euphorbia heterophylla were important species for the crop. Although under a low frequency, outbreaks of Leonurus sibiricus and Gnaphalium spicatum were observed in the areas, increasing their importance in 2007 and 2008. Atrazine was the most used herbicide over the agricultural years, with a low use of other products. Soil cover presented a high variation, but a high number of fields presented a low soil cover. Despite the increase of transgenic soybean in this region, no consistent evidence of changes in weed community resulted from this transition.

Highlights

The regions of Assis, Ourinhos, and Itapeva, in the Paranapanema river basin, are the largest producers of the second corn crop in São Paulo State, with 63.7% of the total produced (Martins et al, 2017), almost always in a succession to soybean
The Assis region is located in the Middle Paranapanema Valley, where the second corn crop has reached an area of at least 120,000 hectares per year since 1994 (Furlaneto and Nardon, 2007)
The production environment of the second corn crop, especially at lower temperatures, has not reduced weed emergence since some of them are specific, such as radish (Raphanus sativus), and others seem to have adapted to autumn/winter, such as southern sandbur (Cenchrus echinatus) and hairy beggarticks (Bidens pilosa), with a less vigorous development, which allows reducing herbicide doses in relation to summer crops (Duarte et al, 2007)

Summary

Introduction

The regions of Assis, Ourinhos, and Itapeva, in the Paranapanema river basin, are the largest producers of the second corn crop in São Paulo State, with 63.7% of the total produced (Martins et al, 2017), almost always in a succession to soybean. Surveys have been conducted in commercial areas to characterize the most problematic weed species and herbicides used (William et al, 2006; Givens et al, 2009; Grey et al, 2014). These monitoring are a valuable tool for documenting the dynamics of herbicide use, as well as the perceptions that guide decisions regarding the selection of these products (Givens et al, 2009)

Objectives

Methods

Results