Integrating plant biotech crops with IPM

Producers have always been at the forefront of the battle­ to manage insects, diseases, weeds and other pests. Fortunately, pest control strategies have continued to evolve over the years to become more effective.

The widespread use of and overreliance on chemical control in the mid to late 1900s, led to the first cases of insect resistance against pesticides. This demonstrated that a single approach to pest control relying only on pesticides, was not a silver bullet. Following these unsustainable trends, the thinking around pest control began to shift in a direction of how best to manage pests optimally, rather than eliminating them. This gave rise to a more comprehensive pest management approach, a concept widely known today as integrated pest management (IPM).

According to the Food and Agriculture Organisation (FAO) of the United Nations, IPM is defined as consideration of all available pest control techniques and other appropriate measures that discourage the development of pest populations, while minimising risks to human health and the environment. It is generally accepted that the basis of an IPM approach is the use of preventive crop protection practices, which rely on an understanding of the environment, crop, pest and natural enemy biology, with the use of optimised farming practices to manage pests. Today’s IPM toolkit comprises the development and use of a wide range of useful technologies and products for pest control, including the cultivation of plant biotech crops with inherent traits for improved pest and weed control.

Biotech crops as a pest management tool
Due to their superior performance and benefits, the most widely adopted biotech crops globally include crops with input traits such as herbicide tolerance (HT) and insect resistance (IR), that have become an integral tool for complementing and enhancing IPM practices in agriculture over the last two decades. The uptake and utilisation of these two plant biotech traits in South Africa have followed a similar trend, with single and stacked combinations of IR and HT traits being the preferred choice for local maize, cotton and soybean producers.

Insect-resistant traits that are commercially available in the market today include mostly insecticidal proteins derived from the soil bacterium, Bacillus thuringiensis (Bt). These Bt insecticidal proteins are toxic to specific lepidopteran pests such as maize stalk borer (Busseola fusca) and African cotton bollworm (Helicoverpa armigera). The main advantage of IR biotech crops over other insect control measures is that they are continuously available within the plant to provide accurate and timely delivery of the active ingredient for more effective control against targeted insects.

The most widely adopted HT crops to date include those with traits that confer resistance to glyphosate. HT biotech crops allow for specific herbicide applications to be sprayed over crops for weed control, without injury to the crops. In this way HT crops provide an additional mode of action within an integrated weed management (IWM) programme. Herbicide-tolerant crops offer producers some distinct benefits by allowing a simplified approach to weed control that is effective, flexible, compatible with reduced tillage practices and with fewer applications of herbicides.

Both IR and HT crop technologies offer producers a vital tool in the fight against weeds and insect pests, with reduced environmental impact and better use of limited resources. It provides a more convenient, flexible and integrated pest control strategy for growers.

Resistance development
All producers are challenged with the simple fact that every insect control method has a limited lifespan because all insects and weeds inevitably fight back by adapting and developing resistance. Resistance development is an ongoing concern in all crop production systems – from conventional to biotech to organic. This requires that producers adopt insect management practices as part of their IPM strategy to delay the onset of resistance, ensuring that any method of eliminating pests, including the deployment of biotech crops, remains effective long into the future.

The development of resistance in IR crops is based on the same principles as the development of resistance to insecticides. Dealing with resistance in IR crops is very different, however, because the insecticidal protein is always present. It is therefore not possible to alternate the mode of action during the season as is recommended for insecticide applications. Also, despite the valuable performance of IR crops in controlling targeted pests, it may occasionally be necessary to supplement with insecticide applications. Under these circumstances, and where insecticides are needed for non-targeted pests, standard insect resistance management (IRM) practices for insecticides should also be maintained. To ensure the durability and long-term effectiveness of IR trait technology, it is essential that producers include some unique strategies for resistance management that are tailored to their specific growing conditions and the pest pressures that they face.

Strategies for resistance management
Two key strategies to address IR in biotech crops include: 1) the mandatory planting of a conventional crop refuge (no IR trait) alongside the biotech field to support a population of susceptible insects that have not been exposed to selection pressure from the IR protein; and 2) the use of stacked traits that combine multiple insecticidal proteins within a single plant, offering different modes of action against the same pest. Both of these strategies work to prevent and delay the build-up of pest immunity against these insect-resistant trait technologies.

It is well known that herbicide resistance in key weed species is largely attributed to overreliance on a single weed control strategy – that is the continuous application of herbicides with the same mode of action. As the cultivation of herbicide-tolerant crops goes hand in hand with the application of herbicides such as glyphosate, the use of diverse weed control strategies is crucial for reducing weed resistance and ensuring the long-term sustainability of HT crops.

The primary goal of resistance management plans for HT crops, therefore, should be to combine as many weed management practices as possible that include crop rotations, multiple herbicidal modes of action, responsible use of herbicides giving special attention to label requirements (dosage rates and timing), integration with local farming conditions and good agricultural practices. Regardless of the deployment of biotech crops, diversity is key for IWM. Therefore, the goal for weed control should always be to combine as many weed management practices as possible to sufficiently reduce selection pressure for the development of resistance.

Promoting responsible management and use of biotech crop protection tools
The addition of a single technology such as biotech crops to augment the IPM toolkit of growers, is not an all-encompassing solution to pest control. Instead, the view towards implementation of IPM should always be to balance the use of one technology with other complementary approaches and avoid relying only on one solution for pest control.

While the introduction of biotech crops has proven its value and demonstrated benefits as a crop protection tool, its future durability and effectiveness are largely dependent on its responsible use – with compliance to IRM being non-negotiable. However, there is no one-size-fits-all plan when it comes to IRM, as insect pressures, farming systems and practices differ from one producer to the next and from region to region. To compensate for these differen­ces, it is important that growers of biotech crops are equipped with adequate knowledge and understanding of the technology and how it works. It also needs to be integrated with good on-farm agricultural practices.

Staying ahead of resistance
As stakeholders in the agricultural value chain, we all have a responsibility to invest in knowledge sharing and training of our growers on responsible use of biotech crops as well as other innovative pest control solutions that form part of the IPM toolkit. In this way we remain several steps ahead of resistance, ensuring that benefits to sustainable agriculture and food security continue to be realised.