Changes in weed species since the introduction of glyphosate-resistant cotton
Jeff Werth A D , Luke Boucher A , David Thornby A , Steve Walker B and Graham Charles CA Agri-Science Queensland, Department of Agriculture, Fisheries and Forestry, Leslie Research Centre, 13 Holberton Street, Toowoomba, Qld 4350, Australia.
B Queensland Alliance for Agriculture and Food Innovation, The University of Queensland, 13 Holberton Street, Toowoomba, Qld 4350, Australia.
C NSW Department of Primary Industries, Cotton Catchment Communities Cooperative Research Centre, Locked Bag 1001, Narrabri, NSW 2390, Australia.
D Corresponding author. Email: jeff.werth@daff.qld.gov.au
Crop and Pasture Science 64(8) 791-798 https://doi.org/10.1071/CP13167
Submitted: 10 May 2013 Accepted: 21 August 2013 Published: 29 October 2013
Journal Compilation © CSIRO Publishing 2013 Open Access CC BY-NC-ND
Abstract
Weed management practices in cotton systems that were based on frequent cultivation, residual herbicides, and some post-emergent herbicides have changed. The ability to use glyphosate as a knockdown before planting, in shielded sprayers, and now over-the-top in glyphosate-tolerant cotton has seen a significant reduction in the use of residual herbicides and cultivation. Glyphosate is now the dominant herbicide in both crop and fallow. This reliance increases the risk of shifts to glyphosate-tolerant species and the evolution of glyphosate-resistant weeds.
Four surveys were undertaken in the 2008–09 and 2010–11 seasons. Surveys were conducted at the start of the summer cropping season (November–December) and at the end of the same season (March–April). Fifty fields previously surveyed in irrigated and non-irrigated cotton systems were re-surveyed.
A major species shift towards Conyza bonariensis was observed. There was also a minor increase in the prevalence of Sonchus oleraceus. Several species were still present at the end of the season, indicating either poor control and/or late-season germinations. These included C. bonariensis, S. oleraceus, Hibiscus verdcourtii and Hibiscus tridactylites, Echinochloa colona, Convolvulus sp., Ipomea lonchophylla, Chamaesyce drummondii, Cullen sp., Amaranthus macrocarpus, and Chloris virgata. These species, with the exception of E. colona, H. verdcourtii, and H. tridactylites, have tolerance to glyphosate and therefore are likely candidates to either remain or increase in dominance in a glyphosate-based system.
Additional keywords: weed survey, glyphosate resistance, species shift, glyphosate-resistant cotton.
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