Seed germination ecology of giant rat’s tail grasses ( <i>Sporobolus pyramidalis</i> and <i>Sporobolus natalensis</i> ) and herbicide options for their control

Abstract Sporobolus natalensis (Steud.) T. Durand &amp; Schinz. and Sporobolus pyramidalis P. Beauv., generally known as giant rat’s tail grasses, are two significant weed species that invade summer fields and pastures in the eastern regions of Australia. This study was conducted to examine seed germination behavior, seedling emergence, and the response of these species to various herbicides. Seed germination and seedling emergence were assessed in response to environmental factors, including alternating temperature regimes (15/5, 20/10, 25/15, 30/20, and 35/25 C), light conditions (dark and light/dark), osmotic potentials (0, −0.1, −0.2, −0.4, −0.8, and −1.6 MPa), and seed burial depths (0, 0.5, 1, 2, and 4 cm). Furthermore, the efficacy of several post-emergence herbicides was evaluated in pots under outdoor environmental conditions. Germination was higher under light/dark (12-h light/12-h dark) conditions than under continuous darkness (24 h). The seeds of both species exhibited significantly higher germination (&gt;95%) under 12-h light at higher temperatures (35/25 C) compared with low (20/10 C) or medium (25/15 C) temperatures. The osmotic potential required to inhibit 50% of maximum germination was −0.77 MPa for S. natalensis and −0.59 MPa for S. pyramidalis . Seedling emergence decreased with increasing burial depth, with no emergence observed from seeds buried at depths of 4 cm. Applying herbicides significantly reduced both species’ seedling survival and dry matter. The most effective herbicides for controlling spring-germinated S. pyramidalis and S. natalensis were haloxyfop, clethodim, butroxydim, glyphosate, glufosinate, and paraquat, which provided satisfactory control of both species. The findings from this study can be used to develop effective management strategies for controlling S. pyramidalis and S. natalensis in agricultural systems.