Abstract

Ryegrass (Lolium multiflorum Lam.) is the main winter weed of crops in Southern Brazil. High competitiveness, adaptability, widespread resistance to herbicides and seed dormancy make the plant a permanent problem. Herbicides, as well as plant growth regulators, can be used as a management option for ryegrass seed production, however there is no consensus among authors at which stage of the plant the application is most effective. Thus, this study aimed to evaluate the production and physiological quality of ryegrass seeds in response to the application of herbicides and plant growth regulators in three stages of plant development (inflorescence emergence, flowering and fruit development). Each treatment consisted of applying two different doses of each of the active ingredients: ammonium glufosinate, clethodim, glyphosate, iodosulfuron-methyl, paraquat and 2,4-D (herbicides); ethephon and trinexapac-ethyl (plant growth regulators), still an untreated control, totaling 17 treatments for each stage of development. The experimental design used was randomized blocks, with three replications. The variables evaluated were: seed production (kg ha−1), thousand seed weight (g), viability (%), germination (%), first germination count (%), dormant seeds (%) and dead seeds (%). The ryegrass seed production reduced 100% with clethodim, glyphosate, ammonium glufosinate or paraquat applied in the inflorescence emergence or flowering stages. In the fruit development stage, all treatments (herbicides and plant growth regulators) caused deleterious effects on seed production, the greatest effect occurred with paraquat (95%). Paraquat, ammonium glufosinate and clethodim affected the physiological quality of the seeds when applied in fruit development stage. This research demonstrated that the application of herbicides in the ryegrass reproductive stage decreases its seedbank replenishment (natural re-sowing), with the potential to harm its progeny.

Highlights

  • Ryegrass (Lolium multiflorum Lam.), known as Italian ryegrass, is characterized as an important and problematic weed from regions of the world’s temperate and subtropical climate

  • Significant differences between treatments were found only for seed production when herbicides and plant growth regulators were applied at this stage of development

  • Glyphosate, ammonium glufosinate, iodosulfuron-methyl and paraquat, regardless of the dose evaluated, reduced seed production by 100%

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Summary

Introduction

Ryegrass (Lolium multiflorum Lam.), known as Italian ryegrass, is characterized as an important and problematic weed from regions of the world’s temperate and subtropical climate. The ryegrass competes intensively for resources of the environment in wheat, oat or barley crops, mainly due to its morphophysiological similarities in development, such as plant height and canopy architecture, since it belongs to the same botanical family [1]. Competition reduces seed production and quality in the infested crop. The presence of ryegrass in wheat and barley crops has been reported with losses in many countries in the world such as Denmark [2], United States [3], Egypt [4], Argentina [5] and Japan [6]. In evaluations in a ryegrass-infested wheat area, reductions of 20% to 30% in yield were observed [5] and may reach a rate of up to 92% [7]. In Brazil, the presence of this weed can reduce wheat yield up to 62% [8]

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