Wednesday, August 24, 2016         

HRAC Mission Statement

  • To foster a responsible attitude to herbicide use. 
  • To support and participate in research, conferences and seminars which serve to increase our understanding of herbicide resistance. 
  • To promote a better understanding of the causes and results of herbicide resistance. 
  • To communicate herbicide resistance management strategies and support their implementation through practical guidelines. 
  • To seek active collaboration with public and private researchers, especially in the areas of problem identification and devising and implementing management strategies. 
  • To facilitate communication between industry representatives


HRAC is an industry-based group supported by Crop Life International. 

Its members are:

In order to ensure effective co-operation and communication, its working groups are divided on a regional basis (Europe, NAFTA and Rest of World). These regional groups interact with an informal network of country committees which are often indirectly linked to HRAC and often led by government researchers. There is no set structure but our co-operation is fueled by our common aim - to manage resistance.

Herbicide Resistance Action Committee (HRAC)

Herbicides are the primary economic means to control weeds and the evolution of herbicide resistant weeds is a problem in modern agriculture.  Herbicide resistance is the evolved capacity of a susceptible weed population to withstand a herbicide application and complete its lifecycle when the herbicide is used at normal rates in an agricultural situation.  The Herbicide Resistance Action Committee (HRAC) is an international body founded by the agrochemical industry to supporting a cooperative approach to the management of herbicide resistance.

Resistance Management Strategies

Resistance often becomes a problem because of high selection pressure exerted on a weed population over several years. This may be a result of repeated use of the same herbicide, or several herbicides with the same site of action and is often associated with crop monoculture as well as reduced cultivation practices. Therefore the key to resistance management is to reduce selection pressure by using a combination of the following techniques:

Mixtures or sequences of herbicides with differing sites of action are important especially to prevent or overcome resistance based on target site differences. To be effective the herbicides used in mixtures or sequences must have similar efficacy against the target weed. If the resistance is based on enhanced metabolism, this technique may also be useful, as the metabolic processes may be specific to certain types of molecule, but an empirical approach is needed to determine the best herbicide combinations.

Crop rotations may allow different herbicides or cultivation techniques to be used and may also provide different competitive environments to shift the weed flora. Set-aside programmes also allow new opportunities to manage populations of resistant weeds.

Cultivation practices may be adjusted if this fits to general agronomic needs. Measures such as stale seedbeds, ploughing or stubble burning (where permitted) can be very effective in reducing weed populations. In some husbandry systems, the grazing off of weeds (including the resistant ones) by sheep or cattle may be possible. In other cropping systems it is possible to use mechanical methods of weed control.

Economic control levels should be the aim, not higher cosmetic levels which increase selection pressure without providing a financial return to the farmer.

Generally, the best approach to resistance management is Integrated Weed Management. This means to utilise all available control methods in an economic and sustainable manner.

General principles of herbicide resistance management

  1. Apply integrated weed management practices. Use multiple herbicide sites-of-action with overlapping weed spectrums in rotation, sequences, or mixtures.

  1. Use the full recommended herbicide rate and proper application timing for the hardest to control weed species present in the field.

  1. Scout fields after herbicide application to ensure control has been achieved. Avoid allowing weeds to reproduce by seed or to proliferate vegetatively.

  1. Monitor site and clean equipment between sites.

For annual cropping situations also consider the following:

  • Start with a clean field and control weeds early by using a burndown treatment or tillage in combination with a preemergence residual herbicide as appropriate.

  • Use cultural practices such as cultivation and crop rotation, where appropriate.

  • Use good agronomic principles that enhance crop competitiveness.

International Survey of Herbicide-Resistant Weeds

HRAC is keen to support the establishment of a worldwide herbicide resistance database. With this aim in mind, HRAC is supporting the worldwide survey of resistant weeds initiated by the Weed Science Society of America. The International Survey of Herbicide-Resistant Weeds is being conducted by Dr. Ian Heap and is located at

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