Performance of RR soybean submitted to postemergence application of glyphosate with a foliar elicitor product

Jamil Constantin,Christiano Lima Lobo De Andrade,Rubem Silvério De Oliveira Júnior,Fellipe Goulart Machado,Guilherme Braga Pereira Braz,Bruno César Silva Pereira

doi:10.1590/1808-1657000492019

Abstract

ABSTRACT With the advent of glyphosate-resistant soybean, postemergence applications of the herbicide have become routine. In this way, problems related to the selectivity of glyphosate have been shown to be increasingly intense, due to the use of increased dosages and applications of the herbicide at unrecommended moments. In order to evaluate the agronomic performance of soybean plants subjected to the postemergence application of glyphosate – both in isolation and together with Crop+ – at different stages and dosage levels, a randomized block design experiment was carried out with two adjacent checks and four repetitions. The treatments consisted of: glyphosate (1296 g·ha-1); glyphosate + Crop+ (1296 + 0.25 g or L·ha-1); glyphosate + Crop+ (1296 + 0.5 g or L·ha-1); glyphosate (2592 g·ha-1); glyphosate + Crop+ (2592 + 0.25 g or L·ha-1); glyphosate + Crop+ (2592 + 0.5 g or L·ha-1); 2 × glyphosate (2 × 1296 g·ha-1); 2 × glyphosate + Crop+ (2 × 1296 + 0.25 g or L·ha-1); 2 × glyphosate + Crop+ (2 × 1296 + 0.5 g or L·ha-1) and Crop+ (0.5 g·ha-1). The phytotoxicity, soil plant analysis development (SPAD) index, height, stand, mass of 100 grains, and yield of the soybean plants were evaluated. The use of Crop+ on soybean plants led to an increase in the SPAD index; the use of Crop+ in association with glyphosate made possible the attenuation of visible symptoms of damage, preventing reductions in crop yield.

Highlights

The advent of soybean cultivars with glyphosate tolerance (RR and later IPRO) brought a series of benefits for the producer, notable among these is the decreased cost of dealing with weeds, an increased range of control, and the nonoccurrence of carryover to crops planted subsequent to the soy because of the absence of residual herbicidal activity (CONSTANTIN et al, 2016; GREEN, 2018)
The scope of the damage caused by the occurrence of resistant weeds is enormous and causes serious concern, but another situation in which reductions in soybean yield have been observed – and at times neglected – is related to the real selectivity that glyphosate demonstrates for cultivars that contain traits conferring tolerance to the herbicide
Evaluation of the phytotoxicity of soybean plants subjected to glyphosate is essential with an aim of evaluating the selectivity that glyphosate shows towards the crop

Summary

Introduction

The advent of soybean cultivars with glyphosate tolerance (RR and later IPRO) brought a series of benefits for the producer, notable among these is the decreased cost of dealing with weeds (when comparing the price of glyphosate in relation to other products used in conventional soybean cultivation), an increased range of control (due to the effectiveness of glyphosate towards mono- and dicotyledon species), and the nonoccurrence of carryover to crops planted subsequent to the soy because of the absence of residual herbicidal activity (CONSTANTIN et al, 2016; GREEN, 2018). To convey the scope of the losses caused by these weeds, it is estimated that the average annual cost of resistance in Brazil, taking into consideration only the system of soybean production, is close to R$ 5 billion ($1 billion USD) per year. This amount could reach as high as R$ 9 billion when including losses in crop yield due to the interference of the weeds in question (ADEGAS et al, 2017). The negative effects that can be seen after the application of glyphosate are related to micronutrient deficiency, lower photosynthetic efficiency, greater water absorption by the plants in order to metabolize the herbicide, and lower soybean nodulation (SERRA et al, 2011; ZOBIOLE et al, 2010a; 2010b; 2012; KRENCHINSKI et al, 2017)

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