Specific guidelines for Group B herbicides

High resistance risk

Globally herbicide resistance to the Group B herbicide mode of action has been confirmed and documented in more than 150 grass and broadleaf weed species across more than 40 countries. Resistance to Group B is extensive and prolific, with tens of millions of hectares affected, in fact it is the most likely herbicide mode of action to develop resistance.

Group B resistance exists in Australia in 26 species (9 grasses) including more than 20,000 populations of annual ryegrass, more than 20,000 populations of annual ryegrass, more than 200 populations of barley grass, brome grass, more than 200 populations of wild oats, paradoxa grass and crabgrass and in at least seventeen broadleaf weeds including more than 5,000 populations of wild radish, common sowthistle, black bindweed, charlock, more than 2000 populations of prickly lettuce, more than 1,000 populations of Indian hedge mustard, Mediterranean (wild) turnip and turnip weed. Resistance has developed in broadacre, rice and pasture situations. In respect to rice three broadleaf weeds, namely dirty Dora, arrowhead and starfruit are known to have Group B resistant populations.

Research has shown that as few as four applications to the same population of annual ryegrass can result in the selection of resistant individuals and as few as six applications for wild radish. A population can go from a small area of resistant individuals to a whole paddock failure in one season.

A significant challenge facing growers managing Group B resistance is the control of brome grass and barley grass in winter cereal crops. Group B herbicides are presently the only in-crop herbicides that provide effective control of these grass weeds and this poses a severe risk of Group B resistance for growers with cereal dominant rotations.

If a pre-emergent application is made with a Group B herbicide for broadleaf or grass weed control, monitor results and, if required, apply a follow up spray; preferably with a non-Group B herbicide for control of escapes and to avoid seed set. If a follow up Group B (post-emergent herbicide) is applied; ensure that complete weed seed set control is achieved.

Whether using Group B herbicides as a pre-emergent, or post-emergent application; consider the use of registered tank mixes with herbicides from other modes of action.

When using a Group B herbicide for post-emergent broadleaf or grass weed control, this should be preceded by a pre-emergent herbicide treatment with other modes-of-action.

  1. Avoid applying more than two Group B herbicide treatments in any four year period on the same paddock. Where more than two treatments are applied introduce alternative control measures to avoid seed set and seed shed in the paddock.
  2. A Group B herbicide may be used alone on flowering wild radish only if a Group B herbicide has not been previously used on that crop.
  3. In all cases if there are significant escapes following the herbicide application consider using another herbicide with a different mode of action or another control method to stop seed set.
  4. Imidazolinone tolerant crops (Clearfield Systems): Where OnDuty®, Midas® and Intervix® are used refer to the Clearfield® Production Systems – best management practice guide. If Sentry® is to be used pre-emergent; consult the Nufarm Best Management Practices Guide.

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.

GROUP BInhibitors of acetolactate synthase (ALS inhibitors), acetohydroxyacid synthase (AHAS)
imazamox (Intervix®*, Raptor®), imazapic (Bobcat I-Maxx®*, Flame®, Midas®*, OnDuty®*), imazapyr (Arsenal Xpress®*, Intervix®*, Lightning®*, Midas®*, OnDuty®*), imazethapyr (Lightning®*, Spinnaker®)
Pyrimidinylthiobenzoatesbispyribac (Nominee®), pyrithiobac (Staple®)

azimsulfuron (Gulliver®), bensulfuron (Londax®), chlorsulfuron (Glean®), azimsulfuron (Gulliver®), bensulfuron (Londax®), chlorsulfuron (Glean®), ethoxysulfuron (Hero®), foramsulfuron (Tribute®), halosulfuron (Sempra®), iodosulfuron (Hussar®), mesosulfuron (Atlantis®), metsulfuron (Ally®, Harmony®* M, Stinger®*, Trounce®*, Ultimate Brushweed®* Herbicide), prosulfuron (Casper®*), rimsulfuron (Titus®), sulfometuron (Oust®, Eucmix Pre Plant®*, Trimac Plus®*), sulfosulfuron (Monza®), thifensulfuron (Harmony®* M), triasulfuron, (Logran®, Logran® B Power®*), tribenuron (Express®), trifloxysulfuron (Envoke®, Krismat®*)

florasulam (Crest®*, Gangster®*,Paradigm®*, Vortex®*, X-Pand®*), flumetsulam (Broadstrike®), metosulam (Eclipse®), pyroxsulam (Crusader®, Rexade®*)

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. * This product contains more than one active constituent

URL: https://croplife.org.au/resources/programs/resistance-management/specific-guidelines-for-group-b-herbicides-doc/specific-guidelines-for-group-b-herbicides-doc-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.