Residual activity of three herbicides following exposure to summer-autumn conditions on the surface of three Western Australian wheatbelt soils

Michael J. Walsh, Benjamin L. Wilson and Stephen B. Powles, Western Australian Herbicide Resistance Initiative, Faculty of Natural and Agricultural Sciences, University of Western Australia, 35 Stirling Highway, Crawley, Western Australia 6009, Australia.


The naturally infertile sandy soils of the Western Australian (WA) wheatbelt are likely to prolong the duration of effective residual activity of residual herbicides following a pre-season application. This study aimed to determine the loss of residual activity of three herbicides following exposure to extended periods of hot, dry and intense sunlight conditions after application to the surface of three typical WA wheatbelt soils. Plant bioassays were used to determine the residual activity of pendimethalin, s-metolachlor and diuron following exposure to these conditions over an 84 day period. Pendimethalin was found to have a high level of residual activity through these conditions on all three soil types indicating that this herbicide could provide effective weed control following a pre-season application. More importantly, there was a uniform rate of loss of pendimethalin activity that allowed the accurate prediction of efficacy of this herbicide over time. This uniform loss of residual activity under these conditions provides the potential for determining an expected period of effective ryegrass control following application. Similarly high levels of residual activity were not observed for s-metolachlor and diuron.

Keywords: Pendimethalin, diuron, s-metolachlor, residual herbicide, pre-season herbicide application.


Plant Protection Quarterly (2007) 22 (3) 113-120.