Specific guidelines for Group H herbicides

Moderate resistance risk

Resistance to the Group H (HPPD) herbicide mode of action 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.

There is one known population of wild radish resistant to Group H herbicides in Australia, however, continued resistance development to this mode of action is inevitable given its continued usage.

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. Where Group H (HPPD) herbicides are used post emergent it’s important to target small weeds with robust rates. Always mix Group H herbicides with an effective alternate mode of action herbicide, such as Group C products like bromoxynil, which are synergistic, Group I products, such as MCPA, or other alternate mode of action herbicides.

Where Group H (HPPD) herbicides are used pre-emergent in cereals, it’s important to use an alternative mode of action as a follow-up spray to control any subsequent survivors. If two Group H herbicides are used in one season, a herbicide from an alternate mode of action should be used after the first or second applications of Group H to control any weed survivors.

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.

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®) 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).

Sugarcane

It is critical to manage weeds effectively to protect sugarcane from yield loss due to competition.  Weed management that relies on Group H herbicides should incorporate Integrated Weed Management (IWM) principles that include chemical and non-chemical methods of weed control.  Chemical methods of weed control should include rotation and/or tank mixing Group H herbicides with herbicides from other modes of action and may also include the use of non-selective knockdown herbicides and techniques such as “double knock” and spot spraying.  Non-chemical methods of weed control include the use of fallow crops, controlling weed seed set, regular slashing area around the crop, good machinery hygiene, mechanical control in plant cane and a trash blankets in ratoon crops.

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 cultural weed control techniques to reduce the weed seedbank. Make sure you mix and rotate herbicides from different mode of action groups. Always consult the product label prior to use.

GROUP H Bleachers: Inhibitors of 4-hydroxyphenyl-pyruvate dioxygenase (HPPDs)
Isoxazoles: isoxaflutole (Balance® Palmero TX®*)
Pyrazoles: benzofenap (Taipan ®), pyrasulfotole (Precept®*, Velocity®*), topramezone (Frequency®)
Triketone: bicyclopyrone (Talinor®*), mesotrione (Callisto®)

* 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. 


URL: https://croplife.org.au/resources/programs/resistance-management/specific-guidelines-for-group-h-herbicides-draft/
Content last updated: June 10, 2020

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 10 June 2020. All previous versions of this strategy are now invalid.