New pre-emergent herbicides for resistant ryegrass and brome grass

| Date: 16 Feb 2010

wagga preston

New pre-emergent herbicides for resistant ryegrass and brome grass

Chris Preston, Peter Boutsalis and Gurjeet Gill
School of Agriculture, Food & Wine, University of Adelaide, PMB1 Glen Osmond SA 5064.

Efficacy of pre-emergent herbicides in different environments**

Over the past five years we have been investigating alternative herbicides for control of trifluralin in annual ryegrass. The compounds of interest include Bayer and Nufarm trial product, triallate (Avadex) and Boxer Gold. All can be effective at controlling trifluralin-resistant annual ryegrass in no-till knife point systems either alone or in mixtures.

One of the problems with pre-emergent herbicides is the requirement for moisture to activate the herbicide product. The performance of Boxer Gold and a Bayer trial product have been generally excellent on trifluralin-resistant annual ryegrass under a variety of environmental conditions (Figure 1). Control with Avadex/trifluralin mixtures appears to be more susceptible to drier environmental conditions. 

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Figure 1: Performance of pre-emergence herbicides on trifluralin-resistant annual ryegrass at Roseworthy, SA (higher rainfall site, left) and Berriwillock, Vic (lower rainfall site, right) in no-till wheat sown using knife points and press wheels.

Under very high rainfall conditions, crop damage can occur if the herbicides are washed down to the crop roots. This is more of a problem with Boxer Gold than it is with the Bayer trial product. The persistence of pre-emergent herbicides in the soil is Bayer trial product > trifluralin > Boxer Gold. Under environmental conditions where extended emergence of annual ryegrass occurs, Boxer Gold will control emergence for a shorter period than trifluralin or a Bayer trial product. All pre-emergent herbicides struggle with very high annual ryegrass populations and should not be relied on alone to control large populations.

Opportunities for pre-emergent herbicides to control brome grass**

With the emerging issues with resistance to post-emergent herbicides in brome grass there is a need to examine alternative products. In 2008 and 2009 we conducted several trials investigating the opportunity for the new annual ryegrass products to control brome grass. These herbicides are not as effective on brome grass as they are on annual ryegrass (Figure 2). However, the Bayer trial product provided 70 to 80% control, about the same as trifluralin/Avadex and metribuzin/Avadex mixtures. This means that pre-emergent herbicides will not be sufficient to manage brome grass on their own and other strategies will have to be included. 
 wagga preston
Figure 2. Performance of pre-emergence herbicides on brome grass at Wokurna, SA (left) and Waikerie, SA (right) in no-till wheat sown using knife points and press wheels.

Contact: Christopher Preston
Phone: 08 8303 7237

GRDC Project UA00098

** Caution: research on unregistered pesticide use.
Any research with unregistered pesticides or of unregistered products reported in this document does not constitute a recommendation for that particular use by the authors or the authors’ organisations. All pesticide applications must accord with the currently registered label for that particular pesticide, crop, pest and region.