Evaluating the double knockdown technique: sequence, application interval, and annual ryegrass growth stage
Catherine P. Borger A and Abul Hashem B CA Department of Agriculture and Food Western Australia, Dryland Research Institute, Great Eastern Highway, Merredin, WA 6415, Australia. Present address: University of Western Australia, Western Australian Herbicide Resistance Initiative, 35 Stirling Hwy, Crawley, WA 6009, Australia.
B Department of Agriculture and Food Western Australia and CRC Australian Weed Management, Centre for Cropping Systems, Lot 12 (PO Box 483), York Road, Northam, WA 6401, Australia.
C Corresponding author. Email: ahashem@agric.wa.gov.au
Australian Journal of Agricultural Research 58(3) 265-271 https://doi.org/10.1071/AR05373
Submitted: 20 October 2005 Accepted: 10 January 2007 Published: 16 March 2007
Abstract
Applying glyphosate followed by a mixture of paraquat + diquat in the same season for pre-planting weed control may reduce the risk of developing resistance to either herbicide. Glasshouse and field experiments at Merredin and Beverly, Western Australia, were conducted over 2 seasons to determine the best herbicide application sequence, growth stage of annual ryegrass at which to apply the 2 herbicides, and application time and interval to be allowed between applications for optimum control of annual ryegrass (Lolium rigidum Gaud.). Annual ryegrass plants were treated at 3 growth stages with either glyphosate 540 g a.i./ha alone, paraquat + diquat 250 g a.i./ha alone, glyphosate followed by paraquat + diquat 250 g a.i./ha, or paraquat + diquat 250 g a.i./ha followed by glyphosate 540 g a.i./ha (the double knockdown treatment). The herbicides were applied at different times of the day, with varied intervals between herbicides when applied in sequence. The glasshouse experiment showed that herbicides in sequence more effectively killed annual ryegrass plants at the 3–6-leaf stage than a single application of either herbicide. Field experiments showed that applying glyphosate followed by paraquat + diquat provided 98–100% control of annual ryegrass plants when applied at the 3- or 6-leaf stage in 2002 and at all 3 growth stages in 2003. Generally, the sequence of paraquat + diquat followed by glyphosate was less effective than the reverse sequence, although the difference was not large. Averaged over 2 seasons, herbicides in sequence were most effective when the first herbicide was applied at the 3- or 6-leaf stage of annual ryegrass. An interval of 2–10 days between applications of herbicides was more effective than 1 day or less. The application time did not significantly affect the efficacy of double knockdown herbicides on annual ryegrass plants under field conditions.
Additional keywords: glyphosate, mixture of paraquat and diquat (Spray.Seed®), daily application time, resistance management, wheat grain yield.
Acknowledgments
We thank the Grains Research and Development Corporation for funding this research, and Nerys Wilkins for technical assistance. Special thanks are due to members of the Western Australian Herbicide Resistance Initiative, University of Western Australia, for their collaboration in this project. We are also grateful to Dr C. Preston, Dr P. Neve, and Prof. S. Powles for kindly previewing the manuscript.
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