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  • Herbicide Resistance In Canterbury

Herbicide resistance in Canterbury

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A FAR survey has identified ryegrass resistant to Group A, Group B and Group G herbicides on a number of farms in the Selwyn District in Canterbury.

Group A includes clethodim, haloxyfop-P and pinoxaden, Group B includes iodosulfuron-methyl and pyroxsulam, while Group G is glyphosate.

The survey was carried out last summer as part of an MBIE funded project, Managing Herbicide Resistance, which is led by AgResearch. It involved FAR staff collecting wild oat, brome and ryegrass plants from wheat and clover paddocks on 48 farms between the Rakaia and Waimakariri Rivers. This represents around 20% of cropping farms in the area. The plants were then forwarded to AgResearch for resistance testing, and to date, resistance has been identified in ryegrass on 13 of the farms. No resistance was found in any of the bromes and the results from the wild oat testing are not yet available.

FAR’s Phil Rolston says the herbicides involved are glyphosate, haloxyfop-P, pinoxaden, clethodim, iodosulfuron-methyl and pyroxsulam.

“The results of this survey, particularly around glyphosate resistance, are causing us some concern. We are now working to understand how to manage such resistance on cropping farms.”

What to do if you are concerned about herbicide resistance on your farm

  • Check paddocks after herbicide application and remove any plants which have ‘escaped’ treatment.
  • Do not allow any ‘escaped’ plants to go to seed.
  • Contact your agrichemical rep or FAR if you believe that ‘escapes’ are the result of resistance, rather than application conditions.

Slowing the development or managing resistance

Consider the use of non-chemical weed control methods. Some of these are outlined in the following FAR Arable Extras:

  • X97 – Mechanical Weeding
  • X98 - Weed seed rain
  • X104 – Stale and false seed beds

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