Influence of Density and Development Stage of Ryegrass on Glyphosate Effectiveness

M.V Fipke,R.A Vidal

doi:10.1590/s0100-83582019370100025

Abstract

ABSTRACT : Glyphosate is one of the main herbicides used to control ryegrass. The objective of this research was to evaluated whether the glyphosate dose-response curve is affected by density of ryegrass plants in two phenological growth stages. To attend this objective, two experiments were carried out in greenhouse (one with Lolium multiflorum and another with Lolium rigidum) and two under field conditions. In the greenhouse experiments, the experimental design was a completely randomized design in a factorial scheme, with factor A as plant density and factor B as glyphosate doses. In the field, two experiments were carried out in a randomized block design in a split-plot scheme. Plots consisted of glyphosate doses (0, 40, 80, 120, 160, 250, and 350 g ha-1), and the subplots consisted of three ryegrass densities (8 plants m-2, 140 plants m-2 with thinning before herbicide application, and 140 plants m-2 with thinning after herbicide application). In one experiment, glyphosate was sprayed at 28 days after emergence (DAE), whereas in another the application was carried out at 51 DAE. High-density ryegrass plants required a higher herbicide dose to obtain the same level of control of low-density plants. In addition to the density effect, an increased glyphosate dose was necessary for the late application to obtain the same level of control when compared to the initial application. Herbicide effectiveness was affected by population density and plant development stage.

Highlights

Ryegrass (Lolium multiflorum L.) is a monocotyledonous, allogamous plant adapted to different types of climate and soil
Both species presented a reduction in the shoot dry mass accumulation as glyphosate doses increased (Figure 1), except for high densities of Lolium rigidum (Figure 1B) when sprayed at a dose of 35 g a.e. ha-1, not differing from the untreated controls
Regarding the species L. multiflorum, the values of D50 (Table 1) for shoot dry mass were 50, 35, and 107.45 g ha-1 of glyphosate for low density (LD), high density with thinning before application (BA), and high density with thinning after application (AA), respectively. These values demonstrate that plants under AA required more than twice the dose to obtain the same control in relation to the plants under LD

Summary

Introduction

Ryegrass (Lolium multiflorum L.) is a monocotyledonous, allogamous plant adapted to different types of climate and soil. This species is characterized by a high seed production, easy dispersion, and high competitive ability for water, light, CO2, and nutrients (Tironi et al, 2014). It is considered one of the main annual weeds in various agricultural crops such as wheat, pasture, canola, oat, among others (Tironi et al, 2014). In Australia, the intensive use of the herbicide diclofop-methyl at low doses has selected resistant ryegrass (Lolium rigidum L.) plants (Michael et al, 2010). Its continued use at different stages of plant development, together with other incorrect practices, has led to the selection of resistant biotypes (Sammons and Gaines, 2014)

Objectives

Methods

Results