Differential Tolerance of Clones of Eucalyptus grandis Exposed to Drift of the Herbicides Carfentrazone-Ethyl and Glyphosate

S.A Santos,A.T Faria,L.D Tuffi-Santos,A.C Alfenas,B.F Sant’Anna-Santos

doi:10.1590/s0100-83582019370100024

Abstract

ABSTRACT: Drift of the herbicides carfentrazone-ethyl and glyphosate may affect the initial growth of eucalyptus. This study aimed to assess the effect of carfentrazone-ethyl and glyphosate drift on photosynthesis, leaf morphoanatomy, and initial growth of two clones of Eucalyptus grandis. Two experiments were carried out in a 2 x 4 factorial scheme, in which factor 1 was represented by two clones of E. grandis and factor 2 by four herbicide underdoses (control, 86.4 g a.e. ha-1 of glyphosate, 3.0 g a.e. ha-1 of carfentrazone-ethyl, and the mixture of 86.4 g a.e. ha-1 of glyphosate + 3.0 g a.e. ha-1 of carfentrazone-ethyl). Herbicide application was carried out by simulating the drift in the lower third of seedling canopy. Assessments were performed 23 days after herbicide application. Both clones presented morphoanatomical changes such as erosion of epicuticular waxes and degeneration of epidermal and parenchymal cells, especially when exposed to carfentrazone-ethyl underdose or its mixture with glyphosate. The clone CLR 383 was the most affected by the tested herbicides and presented the highest injury, lowest initial growth, lowest dry matter, and highest reduction of photosynthetic rate when treated with herbicide mixture, followed by carfentrazone-ethyl and glyphosate underdoses. The initial growth, dry matter, and photosynthesis of the clone CLR 384 were not affected by the carfentrazone-ethyl underdose. Thus, both herbicides applied in isolation or in a mixture reduced the initial growth, dry matter, and photosynthesis of eucalyptus.

Highlights

Chemical control of weeds in eucalyptus forests is a routine and necessary practice in the initial phase of forest formation
The mixture of herbicides with distinct mechanisms of action, but with a synergistic effect, increases the spectrum of action and considerably improves control efficiency (Kumar and Jha, 2015; McCullough et al 2015; Walsh et al, 2014, 2015). Because it presents a desirable efficiency on glyphosate-resistant weeds, such as Commelina spp. (Werlang and Silva, 2002), the herbicide carfentrazone-ethyl has been widely used as an alternative or in mixture with glyphosate. Another important fact is that among the herbicides registered for eucalyptus, only glyphosate and carfentrazone-ethyl are accepted by certification for use in eucalyptus forests (FSC, 2016)
Leaves of both clones directly exposed to the application of this herbicide either in an isolated underdose or in a mixture with glyphosate presented degraded cells in the adaxial epidermis and palisade and spongy parenchyma (Figure 3E and H)

Summary

Introduction

Chemical control of weeds in eucalyptus forests is a routine and necessary practice in the initial phase of forest formation. In areas with constant glyphosate application there are several reports of weeds resistant to this molecule mainly due to the selection pressure (Neve et al, 2003; Duke and Powles, 2008; Powles, 2008; Beckie, 2011; Norsworthy et al, 2011; Green, 2012; Shaner et al, 2009). In this context, the mixture of herbicides with distinct mechanisms of action, but with a synergistic effect, increases the spectrum of action and considerably improves control efficiency (Kumar and Jha, 2015; McCullough et al 2015; Walsh et al, 2014, 2015). Another important fact is that among the herbicides registered for eucalyptus, only glyphosate and carfentrazone-ethyl are accepted by certification for use in eucalyptus forests (FSC, 2016)

Objectives

Methods

Results