Moderate resistance risk

There are currently no known weeds resistant to Group H herbicides in Australia.  Resistance to Group H herbicides is known for a number of populations of Amaranthus species in the United States, which demonstrates the potential for weeds to develop resistance to this mode of action.  Continuous usage of Group H herbicides in the United States has resulted in resistance in Amaranthus species in a relatively short time.

    1. Broadacre cropping: Of particular concern in Australia is the potential for development of Group H resistance in wild radish.  In some areas, because of a lack of alternate herbicide options growers are heavily reliant on Group H herbicides for control of wild radish populations.  It is essential to integrate additional cultural weed control techniques to reduce the seed bank and minimise seed set, thereby decreasing the selection pressure on Group H herbicides.
    2. Fallow: In high summer rainfall areas, weed control in fallow is heavily reliant on herbicides.  Multiple sprays are often required to maintain a clean fallow between winter crops.  Integrated Weed Management principles should be incorporated wherever possible, including cultivation - the double knock technique, grazing and combining more than one mode of action in a single application.To assist in delaying the onset of Group H resistance, rotate and/or tank mix with herbicides from other modes of action.
 
  1. Rice: Where benzofenap has been applied to rice, a follow-up application of MCPA or bentazone and MCPA  is recommended where appropriate to provide a secondary mode of action.  To reduce the likelihood of resistant weeds developing it is recommended that products containing benzofenap (eg. Taipan®, Viper®) not be used in consecutive rice crops.

Synergistic interactions have been documented for several Group H and Group C herbicide combinations.  Where possible, apply a Group H herbicide in combination with a Group C herbicide to maximise efficacy.   Always use the label rate of herbicide whether or not a single active ingredient (eg. isoxaflutole) or combinations of active ingredients are applied (eg. isoxaflutole + simazine, pyrasulfotole/bromoxynil).

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 H Bleachers: Inhibitors of 4-hydroxyphenyl-pyruvate dioxygenase (HPPDs)
Isoxazoles: isoxaflutole (Balance®)
Pyrazoles: benzofenap (Taipan ®), pyrasulfotole (Precept®*,Velocity®*)

* 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