Influence of Density and Development Stage of Ryegrass on Glyphosate Effectiveness

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.Planta Daninha 2019; v37:e019178173 FIPKE, M.V. & VIDAL, R.A. Influence of density and development stage of ryegrass on glyphosate effectiveness 2 comparação à aplicação em estádio inicial. A eficácia de herbicida foi afetada pela densidade populacional e pelo estádio de desenvolvimento das plantas. Palavras-chave: Lolium multiflorum L., Lolium rigidum, época de aplicação, tolerância.

Control of Italian ryegrass and Alexandergrass in corn using different corn sowing date, pre- and post-emergent herbicides

“…The use of residual herbicides reduced the initial LOLMU and URPLA densities favoring their control in post-emergence. In a recent article, the authors concluded that it is more challenging to control GR LOLMU in high densities and that to reach the same level of control as those obtained with low weed density is necessary to increase the herbicide dose (Fipke and Vidal 2019). However, the results of the present study indicate that the application of atrazine + S-metolachlor in corn pre-emergence is a more efficient alternative than increasing the glyphosate rate or even the number of applications in postemergence.…”

“…High density and not adequate stage of GR LOLMU are two factors that make it difficult to control with a burndown application before corn establishment. The poorly controlled plants will likely interfere with corn development and can reduce the crop yield up to 48% (Nandula 2014;Fipke and Vidal 2019).…”

Determination of Minimum Doses of Imazamox for Controlling Xanthium strumarium L. and Chenopodium album L. in Bean (Phaseolus vulgaris L.)

“…In a very recent study, Trezzi et al [46] reported that the retention rate significantly impacts the efficiency of imazamox, which supports our results. However, it should be kept in mind that the effectiveness of herbicides is significantly affected by the weed development stage and density; if the stages increase further, the weeds become more tolerant and the efficacy of the herbicides decreases [47]. Therefore, the application time is crucial for reaching satisfactory control with the lowest herbicide doses.…”