Moderate resistance risk
Globally herbicide resistance to the Group L herbicide mode of action has been confirmed and documented in more than 30 weed species across 16 countries
Group L resistance exists in Australia in annual ryegrass, and in 2 species of barley grass across more than 100 populations, 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:
The risk of resistance to Group L herbicides is higher in minimum/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.
1. The double knock technique is defined as using a full cut cultivation OR the full label rate of a paraquat-based product (Group L) following the glyphosate (Group M) knockdown application
The above recommendations should be incorporated into an Integrated Weed Management (IWM) program. In all cases try to ensure surviving weeds from any treatment do not set and shed viable seed. Keep to integrated strategies mentioned in this brochure including rotation of mode of action groups. Make sure you rotate between products from different mode of action groups. Always consult the product label prior to use.
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.
Content last updated: June 28, 2019