Herbicide-tolerant crops in Integrated Weed Management (IWM) systems

Scientists have proposed five actions to facilitate the incorporation of herbicide-tolerant crops in Integrated Weed Management (IWM) systems and have emphasised that the same approach should be taken whether the crops are conventionally bred or genetically modified to be herbicide-resistant.

The adoption of herbicide-tolerant crops and their associated agronomic practices can facilitate effective weed management, the researchers say, overcoming the growing problems with herbicide resistance in weeds and helping to prevent the environmental issues associated with the intensification of agriculture.

However, several factors may limit the integration of herbicide-tolerant crops and their related farm management practices in Integrated Weed Management systems. Writing in Critical Reviews in Biotechnology, the scientists have therefore proposed five actions to facilitate the incorporation of herbicide-tolerant crops in IWM systems in the European Union. They base their recommendations on experience gained in countries where herbicide-tolerant crops (such as oilseed rape pictured right) are widely grown, whether they be conventionally bred or genetically modified.

IPM is necessary

Conventionally bred (CHT) and genetically modified herbicide-tolerant (GMHT) crops have changed weed management practices and made an important contribution to the global production of some commodity crops, say the authors. However, they add, the farm management practices associated with the cultivation of herbicide-tolerant crops can further deplete farmland biodiversity and accelerate the evolution of herbicide-resistant weeds.

Diversification in crop systems and weed management practices can enhance farmland biodiversity and reduce the risk of weeds evolving herbicide resistance. Therefore, they write, herbicide-tolerant crops are most effective and sustainable as a component of Integrated Weed Management systems.

Treat CHT and GMHT crops equally

Cultivation of crops with CHT traits presents similar weed management challenges and agronomic risks as crops with GMHT traits, they note. However, the EU regulatory framework distinguishes between CHT and GMHT crops. All GMHT crops are regulated while CHT crops are not.

This is paradoxical, say the authors, because the cultivation of herbicide-tolerant crops in North and South America has clearly revealed that the most severe environmental problems resulting from their cultivation are primarily related to agronomic factors, particularly herbicide-use practices, rather than genetic or biological factors. In other words, they present similar advantages and disadvantages. CHT and GMHT cultivars therefore require the same diverse management strategies to address environmental issues.

Five actions proposed

Integrated Weed Management advocates the use of multiple effective strategies and tactics to manage weed populations in a manner that is economically and environmentally sound. In practice, however, the potential benefits of IWM with herbicide-tolerant crops are seldom realized because a wide range of technical and socio-economic factors hamper the transition to Integrated Weed Management.

Effective weed management without herbicide use is not presently conceivable in regular intensive farming systems, write the authors. Herbicide diversity is therefore a key to weed control. In the long-term, cropping systems that are more diverse and less reliant on herbicides have to be adopted by farmers to mitigate the risk of weed resistance evolution.

Although such sustainable practices may be more costly for growers to implement in the short-term, they will be beneficial in the longer term, especially if appropriate policies and incentives are put in place. Such policies and incentives should include the following five actions, say the authors:

1.    Education programmes to maintain and improve knowledge of weeds and their management
2.    Revision of current stewardship programmes
3.    Integration of socio-economic studies to understand and change growers’ attitudes and behaviour
4.    Development of adequate public policy
5.    Regulatory revisions