South African Maize Farmers Urged to Improve Refuge Planting to Protect Bt Technology

South African maize farmers have been urged to improve compliance with refuge planting requirements to slow the development of insect resistance and protect the long-term effectiveness of Bacillus thuringiensis (Bt) maize technology. The warning comes as emerging resistance in maize stem borer populations highlights the importance of responsible pest management and careful use of genetically modified (GM) maize. Agricultural entomologist Professor Johnie van Rensburg raised the concern during a Bayer discussion on insect resistance management. Experts at the discussion emphasised that farmers, seed companies, researchers and other agricultural stakeholders must work together to preserve the benefits of modern maize technology. Their message was clear: consistent refuge planting and responsible technology use are essential to protecting South Africa’s maize production in the years ahead.

Van Rensburg explained that populations of the maize stem borer, Busseola fusca, are showing emerging resistance to Bt maize in certain parts of South Africa. The problem remains geographically limited, with resistance particularly identified in parts of the Eastern Cape. He stressed that resistance develops through natural evolution as insects carrying resistant genes survive exposure to the Bt toxin and reproduce. Over time, these insects can make up a larger proportion of the population, increasing the risk that Bt maize will become less effective against the pest. Van Rensburg explained that the change does not mean the maize hybrid is deteriorating or that the toxin inside the plant is becoming weaker. Instead, the insect population is gradually developing the ability to survive the technology designed to control it.

This distinction is important for farmers because it helps explain why resistance management must focus on insect populations and farming practices. Bt maize contains traits that allow the plant to produce proteins derived from Bacillus thuringiensis, which help protect it against certain insect pests. The technology has become an important part of South African maize production because it can reduce damage caused by target pests and support more reliable crop protection. However, its effectiveness depends on responsible management and compliance with recommended planting practices. When farmers do not follow resistance management requirements, they increase the risk that resistant insects will survive and multiply. Protecting Bt maize therefore requires more than selecting the right seed hybrid. It also requires farmers to understand how resistance develops and take practical steps to slow it down.

One of the most important measures is refuge planting. A refuge is an area of non-Bt maize planted alongside Bt maize to maintain a population of insects that remain susceptible to the Bt toxin. These susceptible insects can mate with potentially resistant insects emerging from Bt maize fields. This mating reduces the likelihood that resistant genes will become widespread in future generations. The refuge strategy is based on the principle that Bt maize should produce sufficient toxin to kill susceptible stem borers, while non-Bt maize provides a source of susceptible insects. Both components must work together for the strategy to deliver its intended benefit. Farmers who fail to establish the required refuges weaken an important part of the resistance management system.

Van Rensburg warned that poor compliance with refuge planting requirements and potentially insufficient toxin expression could contribute to resistance development. He encouraged farmers to continue planting refuges, even where resistance has already been detected. The presence of emerging resistance in certain areas does not mean that Bt maize has lost its value across South Africa. Many production regions have not recorded resistance, while the technology continues to provide protection against other important stem borer species. Farmers should therefore avoid making decisions based on the assumption that the technology no longer works. Instead, they should follow refuge requirements and seek guidance on appropriate resistance management practices for their production areas.

The importance of preserving Bt maize extends beyond controlling stem borers. Van Rensburg referred to research indicating that Bt maize delivered an average annual yield gain of 11% over a period of 20 years. The reported aggregate income benefits for South African maize farmers reached R21 billion over that period. These gains demonstrate the economic contribution that insect-resistant maize technology has made to the country’s grain sector. Better pest control can help farmers protect crop yields and reduce losses caused by insect damage. If resistance spreads widely, however, farmers could lose some of the advantages that have supported production and profitability. Maintaining the effectiveness of Bt maize is therefore an economic priority as well as an agricultural responsibility.

The technology has also contributed to reduced insecticide use in maize production. Over a 15-year period, approximately 20 million hectares were not sprayed, representing a substantial reduction in the area exposed to insecticide applications. This can provide environmental benefits by reducing the exposure of beneficial organisms to broad-spectrum insecticides. It can also support more targeted pest management where Bt maize controls the insects it was designed to manage. These benefits depend on the continued effectiveness of the technology. If resistance becomes widespread, farmers may face greater pressure to use alternative control measures, including insecticides. Responsible stewardship can help protect both the production and environmental value of Bt maize.

Francois Wolvaardt, DEKALB seed and trait business portfolio manager for Africa, also highlighted the need for farmers to comply with refuge requirements. Biotechnology products are widely used in South African maize production, with approximately 80% of the country’s maize hectares planted with products offering insect control or herbicide tolerance. This level of adoption shows how strongly the grain industry relies on biotechnology to support crop production. Wolvaardt emphasised that sufficient refuge planting is one of the most important actions farmers can take to protect the value these technologies provide. Farmers must treat refuge planting as a necessary part of their production plans rather than an optional activity. Consistent compliance across farming operations can help slow resistance development and extend the useful life of Bt maize technology.

Field monitoring is another important part of effective insect resistance management. Experts advised farmers to scout their maize fields regularly and report unexpected crop damage as early as possible. Early detection allows farmers to investigate possible pest problems before they become more difficult to manage. Stem borer larvae are generally easier to control when they are still small, making timely monitoring especially important. Farmers should pay attention to unusual feeding damage and follow appropriate reporting and control procedures when they suspect a problem. Sharing observations with relevant agricultural professionals can also help identify emerging resistance and improve the industry’s understanding of pest activity across production areas.

Post-harvest management can further contribute to reducing maize stem borer populations. After harvesting, farmers can disturb or destroy maize stubble to expose overwintering larvae to natural enemies and unfavourable environmental conditions. This can help reduce the number of pests that survive between growing seasons. Managing crop residues forms part of a broader approach to integrated pest management, which combines different practices to reduce pest pressure. Farmers should consider these measures alongside refuge planting, field scouting and other recommended control strategies. No single practice can address every resistance risk, but combining appropriate measures can improve the overall effectiveness of pest management.

Maria Vnuchkova, Bayer’s value proposition lead, reinforced the importance of cooperation across the agricultural value chain. She described stewardship as a shared responsibility involving farmers, industry, researchers and the media. This approach recognises that insect resistance does not affect only individual farms or seed companies. Its development and spread can have consequences for the wider maize sector, including farmers who depend on Bt technology for crop protection. Cooperation helps ensure that information about resistance, refuge requirements and emerging pest threats reaches the people who need it. It also encourages a consistent approach to protecting agricultural technologies that deliver value across the industry.

South African maize farmers have an important role to play in slowing insect resistance and preserving the benefits of Bt maize. Consistent refuge planting, regular field scouting, early reporting and responsible post-harvest management can all contribute to more effective resistance control. The emerging resistance of Busseola fusca in parts of the Eastern Cape should serve as a warning, but it does not mean that Bt maize has lost its usefulness across the country. Farmers who follow recommended stewardship practices can help reduce the risk of resistance spreading into other production areas. Protecting Bt technology requires informed decisions and cooperation throughout the agricultural value chain. By improving refuge compliance today, maize farmers can help safeguard crop protection, farm income and the long-term sustainability of South Africa’s grain production.