Scientists test new biological alternatives to toxic pesticides

A field of young sugar beet plants growing on a Norfolk farm last spring could easily have been mistaken for a land art installation, as blue and red rectangles decorated the plot.

The beet goes on: ‘camo-cropping’ uses dye to make sugar beet crops harder for aphids to detect ©

In fact, it was a trial of a novel way of protecting crops from insect pests, known as ‘camo-cropping’. This is just one of a vast range of non-chemical methods now being tested, or used, as an alternative to toxic pesticides such as neonicotinoids. New approaches are needed as use of these pesticides is being increasingly restricted around the world for environmental reasons.

Camo-cropping involves spraying non-toxic fabric or food dyes on the field — covering the soil and the young plants — so as to reduce the colour difference between the bare earth and beet leaves. Aphids rely partly on this colour contrast to home in on crops. And these insects can be a devastating pest for beet growers, not because they eat the leaves but because they transmit a group of plant pathogens called virus yellows.

This first year’s camo-cropping trial is unlikely to give clear results because of the summer’s unusual weather patterns, including exceptional heat and drought. But it will continue next year, says David Jones, farm manager for the Morley Agricultural Foundation, which is hosting the trial for the British Beet Research Organisation (BBRO).

Dyes are not the only way of camo-cropping, though. Another method is to camouflage the young beet plants by sowing barley among them to mask the soil. Cereal camo-cropping is also being tried at Morley.

Camo-cropping is part of an integrated pest management (IPM) system to protect beet from aphids, which BBRO is developing with support from Defra, the UK government’s food and farming department. The overall project is called ABCD of Aphid IPM, says its leader Alistair Wright.

A stands for attractants or alternative hosts — plants such as brassicas that aphids prefer to sugar beet. Blocks or strips of brassica (radish and oilseed rape) are planted alongside the beet crop to lure away the hungry insects.

Beneficial insects — natural predators of aphids such as ladybirds and lacewing larvae — are the B in ABCD. ″They can eat 300 aphids a week,″ says Wright. To draw in naturally occurring predators, wild flower strips are planted close to the beet field.

Creating a buzz: wild flower strips help attract predatory insects that will devour pests on neighbouring crops

In addition, commercially available beneficial insects can be released into the environment. ″They have been used very successfully in horticulture, particularly in glasshouses, where they are not going to wander off and you have nice controlled temperatures for them,″ says Wright.

″One issue is the sheer quantity you need to cover the UK crop, which can be around 100,000 hectares,″ he adds, ″and you have to make sure they’re hearty enough to survive the fluctuating temperatures we often experience.″

Finally, D stands for deterrents: plant-derived oils including garlic, mint and lavender oil, which are sprayed on to the beet plants to put off aphids. ″There is some evidence that these might work but nothing really solid,″ says Wright. ″We need to trial a range of possible deterrents on a large enough scale to assess their interaction with the aphids and the crop.″

After small-scale trials this year, the ABCD programme will get going in earnest in 2023. The first step will be to discover which, if any, of the approaches work. Then will come the issue of whether they can be introduced cost effectively to supplant or supplement chemical pesticides.

While BBRO is working locally on single-crop IPM, a large programme of work to assess and implement biological alternatives to chemical pest control is being undertaken globally by Cabi (formerly the Centre for Agriculture and Bioscience International). This is an international non-profit organisation based in the UK and funded by governments and development agencies around the world.

Methods range from the introduction of live creatures — usually insects or microorganisms — that prey on plant-eating pests to the application of biological molecules (as opposed to synthetic chemicals) that kill or deter pests.

″A major challenge is that, for decades, growers have had exceptionally effective chemistry to rely on, with products and active ingredients that are simple to use,″ says Steve Edgington, leader of Cabi’s biopesticides group. ″With a lethal chemical, the pest will be knocked down immediately — job done. With biopesticides, you often need different techniques and different thought processes.″

xamples from Cabi’s extensive portfolio include: a biopesticide called Green Muscle derived from fungus to fight voracious desert locusts in Africa; another fungal derivative to prevent cabbage stem flea beetles ravaging oilseed rape in the UK; a wasp released to attack Asian corn borer moths in Asia; micro-organisms applied to coffee plants in Colombia to infect berry borer beetles; and an array of biopesticides and botanical methods being deployed against fall armyworm, an invasive maize pest, in Africa and Asia.

In comparison, chemical pesticides are a relatively limited range of compounds but they sell in far larger quantities — and still represent a more valuable, growing market. According to Fortune Business Insights, the global crop protection chemicals market is projected to grow from $59.4bn in 2021 to $81.7bn in 2028, a compound annual growth rate of 4.66 per cent.

Analysts at industry specialist Dunham Trimmer say the biocontrol sector is growing by 15-18 per cent annually but will not reach a value of $10bn until 2025, when it will represent 10 per cent of the total plant protection market.

Making the most of biopesticides requires far better information about local weather conditions, soil analysis and crop monitoring than is the case with chemical alternatives, Edgington explains. However, Cabi has developed a digital tool, the BioProtection Portal, to help with this.

″The knowledge about biopesticides among growers and their advisers is increasing but it is still massively lacking,″ he says. ″There are so many components to using them properly, especially the microorganisms.″

Even so, the long-term benefits of moving away from chemical control are immense, Edgington stresses. ″Overuse of synthetic pesticides is destroying some soils. In the long term, you are safeguarding soil health, plant resilience and your crop production with biological control.″