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202409 Fresh Quarterly Issue 26 15 Roma Gwynn
Issue 26September 2024

A rational approach to biocontrol

Successful incorporation of biological control in integrated pest management programmes requires in-depth knowledge and excellent execution. By Anna Mouton.

Integrated pest management has existed since the 1950s but is only now becoming more widely implemented. “The Food and Agriculture Organization, which is part of the United Nations, defines it as proactively favouring the registration of less hazardous products where such alternatives are viable and available,” said Dr Roma Gwynn.

Gwynn is a biorational specialist with nearly four decades of experience as a researcher and consultant. Biorational crop protectants are relatively non-toxic compounds derived from or structurally like biological substances.

There are four broad categories of biological crop protectants: macrobials, microbials, natural substances, and semiochemicals, as defined by the International Biocontrol Manufacturers Association.

Macrobials are natural enemies such as predators and parasitoids. Microbials are microorganisms or their products. Semiochemicals are communication chemicals. Natural substances include everything that isn’t a microbial or a semiochemical.

“Biopesticides and biostimulants are sometimes confused. Biopesticides are used to manage pests and diseases. Biostimulants work to improve plant health,” clarified Gwynn. “They are different technologies with different regulatory pathways.”

The global market for biological technologies is booming, with an estimated annual growth of 15% and an expected value of USD 10 billion by 2025. Of the approximately 500 plant-protection products currently registered in the European Union, over 40% are biocontrol technologies.

Gwynn highlighted the example of Brazil, where more than 600 biocontrol products are registered for over 200 targets. “One reason Brazil has been so successful in getting more products to the marketplace is that they changed their regulatory system to speed up product availability,” she said.

Surveys found that 98% of Brazilian farmers report being happy with biocontrol and willing to use it again. Interestingly, biopesticide use in Brazil isn’t limited to speciality or high-value horticultural crops but has also been effective in commodity crops in open environments.

The benefits of biologicals

“One of the things people often forget is that we’re using biopesticides in an agroecosystem,” said Gwynn. “And we’re trying to create as much diversity in that system as possible because that’s what makes plants resilient.”

Diversity includes everything from the microorganisms around the plant roots to the natural predators and parasitoids around its leaves. “We’re dealing with a very complex system, trying to move it in favour of the crop rather than in favour of the pest,” she explained.

This contrasts with conventional synthetic pesticides where the aim is maximal killing of pests and diseases.

Gwynn illustrated this concept with a Norwegian example of aphid control in wheat. Researchers found that wheat produces a pheromone to attract predatory lacewings. Growers could capitalise on the wheat’s natural reaction by planting flower borders to increase lacewing populations.

“So, the growers aren’t killing anything,” she said. “They’ve increased the ecosystem biodiversity and encouraged more natural enemies, creating a virtuous circle of integrated pest management that can work well.”

She shared the findings of a report by the Institute for European Environmental Policy examining biocontrol’s benefits. These included enhanced plant protection, ecosystem services, and soil health. Biopesticides also tend to have a better safety profile, reducing the risk of farmworker and consumer exposure to toxic chemicals.

Gwynn’s own surveys of growers worldwide have identified that although direct killing of the target and improved yields and quality were the primary reasons for the uptake of biological technologies, there were many other reasons.

“Strawberry growers mentioned one I hadn’t previously considered,” she said. “Biologicals have no entry or harvest interval.” This means that workers can return to manage or harvest the crop immediately after application, improving workforce utilisation and postharvest fruit quality.

This shows how integrated pest management is a whole-farm practice supported by biorationals.

Bringing in biorationals

Gwynn presented a pyramidal graphic of integrated pest management in which agronomic practices — the right management of the right plant in the right place — form the base. The next level is monitoring.

“With the rise of digital agriculture and good sensing, we can see better monitoring and forecasting, not just on a landscape scale but on individual farms and in individual fields,” commented Gwynn.

“This is beginning to impact the amount of crop protection inputs. Crop protection is perhaps going into part of rather than a whole field. They’re not applied prophylactically but are timed to the appearance of pests or diseases.”

The next step after monitoring is physical intervention, followed by biological interventions. Gwynn pointed out that biologicals such as predator releases and biopesticides are only used when agronomical and physical interventions fail, and chemicals should only be used when biologicals fail.

“Chemicals are your plant-protection technology of last resort,” she said. “We must look after the chemistry we have so we don’t overuse it and build resistance.”

Gwynn wants a mind shift around the meaning of efficacy. She believes that it’s unrealistic and unnecessary to expect biopesticides to achieve 80% control. The goal of an integrated pest management programme should be maintaining pest and disease levels below the economic damage threshold — not exterminating them.

If growers monitor conscientiously, they can respond to pest increases timeously and prevent population explosions without reaching for chemical pesticides. Biopesticides with efficacies of 50% or less will do the job.

However, Gwynn admits that biopesticides don’t always perform as consistently and predictably as synthetics. She directed growers to a free online webinar that provides guidelines on the timing and application of biopesticides to optimise efficacy and reliability. The underlying research was done in greenhouses, but the principles apply to other horticultural systems.

“Biopesticides are a different approach to crop protection and integrated pest management,” she summarised. “They require a lot of knowledge and good monitoring and sensitivity. Growers need to be very thoughtful about when and how to use them. But this is the modern plant-protection technology.”

Watch Gwynn’s presentation on the Hortgro YouTube channel.

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