Specific guidelines for Group C herbicides

Moderate resistance risk

Globally herbicide resistance to the Group C herbicide mode of action has been confirmed and documented in more than 70 grass and broadleaf weed species across more than 40 countries. Resistance to the Group C mode of action is common; in fact, it is the third most likely herbicide mode of action to develop resistance.

Group C resistance exists in 8 weed species across more than 100 weed populations including more than 50 populations of annual ryegrass, more than 20 populations of wild radish, liverseed grass, squirrel tail fescue (silver grass), dwarf (stinging) nettles, Indian hedge mustard and barnyard grass (“at risk weeds”).

In all situations the resistance status of “at risk weeds” should be determined prior to sowing. Resistance has developed in broadacre, horticultural and non-crop situations. CropLife Australia gives specific guidelines for the use of Group C herbicides in all situations and particularly in triazine tolerant (TT) canola, and canola with both glyphosate tolerance and triazine tolerance (TT-RR canola) following increasing reports of resistance development: 

  • For “at risk weeds”, avoid using Group C herbicides as the only means of control in the same paddock in consecutive years.
  • Watch and record weed escapes in paddocks with a long history of Group C use.
  • Control survivors to prevent seed-set using a herbicide with a different Mode of Action to Group C or use another weed management technique.
  • Avoid dry sowing in heavily weed infested paddocks. Wait for a germination of weeds after the opening rains in weedy paddocks and use a pre-plant knockdown or cultivation to maximise weed control at this stage.

1. TT Canola

Growing TT Canola in a paddock treated with triazine herbicides in the previous season is a high resistance risk and is not recommended.

For ryegrass control, use simazine, atrazine, metribuzin or terbuthylazine plus a pre-emergence herbicide with a different mode of action (eg trifluralin) prior to sowing. If necessary, follow-up with a post emergent herbicide with a different mode of action (eg clethodim) to control escapes from pre-emergent treatments.

2. TT-RR Canola

Refer to the specific guidelines for Group M herbicides in addition to those given here for triazine herbicides.

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.

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.

CHEMICAL FAMILYACTIVE CONSTITUENT (FIRST REGISTERED TRADE NAME)
GROUP CInhibitors of photosynthesis at photosystem II (PS II inhibitors)
Amides: propanil (Stam®)
Benzothiadiazinones: bentazone (Basagran®, Basagran® M60*, Lawnweeder plus®*)
Nitriles:bromoxynil (Barrel®*, Buctril®, Buctril® MA*, Buffalo Pro Weedkiller®*, Eliminar C®*, Flight®*, Jaguar®*, Talinor®*, Triathlon®*, Velocity®*), ioxynil (Actril DS*, Totril®,)
Phenylcarbamates:phenmedipham (Betanal®)
Pyridazinones:chloridazon (Pyramin®)
Triazines: ametryn (Amigan®*, Gesapax® Combi*, Krismat®, Primatol Z®), atrazine (Gesapax® Combi*, Gesaprim®, Primextra® Gold*), cyanazine (Bladex®), prometryn (Bandit®*, Cotogard®*, Gesagard®), propazine (Agaprop®), simazine (Brunnings RTU Path Weeder®*, Gesatop®, Yates Onceyear Path Weeder®*), terbuthylazine (Firestorm®*, Palmero TX®*, Terbyne®), terbutryn (Agtryne® MA*, Amigan®*, Igran®)
Triazinones: amicarbazone (Amitron®*), hexazinone (Bobcat I-Maxx®*, Velmac Plus®*, Velpar® K4*, Velpar® L), metribuzin (Aptitude®*, Sencor® )
Uracils: bromacil (Hyvar®, Krovar®*), terbacil (Eucmix Pre Plant®*, Sinbar®, Trimac Plus®*)
Ureas:diuron (Karmex®, Krovar®*, Velpar® K4*), fluometuron (Bandit®* , Cotogard®*, Cotoran®), linuron (Afalon®), methabenzthiazuron (Tribunil®), siduron (Tupersan®), tebuthiuron (Graslan®)

* This product contains more than one active constituent


URL: https://croplife.org.au/resources/programs/resistance-management/specific-guidelines-for-group-c-herbicides-2/specific-guidelines-for-group-c-herbicides-2-draft/
Content last updated: June 28, 2019

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

The information given in this strategy is provided in good faith and without any liability for loss or damage suffered as a result of its application and use. Advice given in this strategy is valid as at 27 June 2019. All previous versions of this strategy are now invalid.