Moderate resistance risk

Group L resistance exists in Australia in annual ryegrass, barley grass (2 species),blackberry nightshade, crowsfoot grass, capeweed , pennsylvanian cudweed, squirrel-tailed fescue (silver grass)and small square weed.  Most instances have occurred in longterm lucerne stands treated regularly with a Group L herbicide but Group L resistant barley grass has also occurred in no-till situations.

The following factors are common to most cases of Group L resistance:

  • A Group L herbicide is the major or only herbicide used;
  • A Group L herbicide has been used for 12 – 15 years or more; and
  • There has been minimal or no soil disturbance following application.

The risk of resistance to Group L herbicides is higher in zero tillage broadacre cropping. Other high resistance risk situations include: irrigated clover pivots, orchards, vineyards or pure lucerne stands where frequent applications of a Group L herbicide are made each season, cultivation is not used and there is reliance on a Group L herbicide alone for weed control.

To assist in delaying the onset of resistance, consider alternating Group L herbicides with herbicides from other modes of action. For example, (Group N) eg glufosinate or (Group Q) eg amitrole or (Group M) eg glyphosate.

Below are strategies that address these high resistance risk situations to reduce the risk of Group L resistance developing.

Zero Tillage

  1. Rotate Group L herbicides with other knockdown herbicides with a different mode of action For example (Group M) eg glyphosate
  2. Consider utilising the double knock technique where glyphosate is sprayed first followed within 1 - 7 days by a paraquat application.  A full label rate for the weed size targeted should be used for the paraquat application for resistance management. A full label rate for the weed size targeted should be used for resistance management.
  3. Consider occasional mechanical cultivation to aid weed control.

Lucerne

  1. If using a Group L herbicide for winter cleaning, where possible include another mode of action eg. Group C.
  2. Use alternative modes of action to selectively control grass and broadleaf weeds.
  3. Rotate Group L herbicides with other knockdown herbicides with a different mode of action for example (Group M) eg glyphosate prior to sowing lucerne and prior to sowing future crops in that paddock.

Horticulture

  1. Rotate Group L herbicides with other knockdown herbicides with a different mode of action. For example (Group N) eg glufosinate or (Group Q) eg amitrole or (Group M) eg glyphosate
  2. Where possible use residual herbicides (that are effective on the same weeds as the Group L herbicides) where applicable either alone or in mixture with Group L herbicides.
  3. Where possible use alternative modes of action to selectively control grass and broadleaf weeds.
  4. Consider using the double knock technique where glyphosate is sprayed followed within 1-7 days by a paraquat application.  A full label rate for the weed size targeted should be used for the paraquat application for resistance management.

All the above recommendations should be read in conjunction with the Integrated Weed Management (IWM) strategies

CHEMICAL FAMILY ACTIVE CONSTITUENT (FIRST REGISTERED TRADE NAME)
GROUP L Inhibitors of photosynthesis at photosystem I (PSI inhibitors)
Bipyridyls: diquat (Reglone®, Spray Seed®*), paraquat (Alliance®*, Gramoxone®, Spray Seed®*)

* This product contains more than one active constituent

List of chemical families, approved active constituents and, in parenthesis, the trade name of the first registered product or successor.  Refer to the APVMA website (www.apvma.gov.au) to obtain a complete list of registered products from the PUBCRIS database. 


CropLife Australia’s Resistance Management Strategies provide a guide for crop protection product rotation through product groups.  The strategies are a useful tool that supports farmers’ adoption of resistance management.

All crop protection products must be handled and applied strictly as specified on the product label or APVMA permits.  These Resistance Management Strategies do not replace product labels.  They are a guide only and do not endorse particular products, groups of products or cultural methods in terms of their performance.  It is important to check with the Australian regulator’s (APVMA) product database for contemporary information on products and active constituents.  The database can be sourced through www.apvma.gov.au