Alternative controls

More producers are developing non-chemical pest and disease control options in response to the ever decreasing pool of products available for growers to protect their crops, Gavin McEwan reports.

Crop protection: developing more products could make control easier while also offering potential to increase yields. Image Deere & Company
Crop protection: developing more products could make control easier while also offering potential to increase yields. Image Deere & Company

The diminishing range of crop-protection products available to British growers threatens any moves to increase national production, self-sufficiency and food security. Fortunately, a growing number of companies are developing alternatives to established chemical solutions to pest and disease control.

Explaining the predicament, British Growers Association chief executive Jack Ward says: "The issue of crop protection affects a large proportion of the food manufacturing process in the UK. Developing a wider range of crop-protection products could make it easier for growers to protect their crops and gain a greater yield. But without investment, food supplies could be lowered drastically."

He adds: "The Government needs to maintain a robust line against the EU proposal to introduce a hazard-based approach to active ingredient classification - and it needs to give more support for Extensions of Authorisation for Minor Use for fresh produce to ensure that a wide range of crop-protection products can be cleared for use more quickly and cheaply."

Prohibitive authorisation costs

The cost of authorising products for more niche crops can often be prohibitive, he explains. "Currently there is only a finite area for many fresh crops to be grown in the UK, with certain crops only produced in specific parts of the country. It is not always financially viable to invest in crop-protection products for crops that have a limited yield, which will ultimately lead to fewer crop-protection products being available."

While biopesticides represent a promising alternative: "They too are subject to a detailed regulatory scrutiny process that makes the development process expensive," says Ward.

However, other "non-synthetic strategies" under development also show promise, he adds. "Continuing research in the use of predators and elicitors could see a crop's natural chemical defence mechanism activated, which would negate the need for further crop-protection products."

Indeed a range of approaches was in evidence at last month's Fruit Focus event, with even large, established agro-chemicals firms emphasising the role of non-chemical solutions.

According to Syngenta Bioline, western flower thrips' (Frankliniella occidentalis) growing resistance to conventional crop-protection products is becoming a major problem in strawberry production. A recent study showed that adding its aggregation pheromone ThripLine to sticky roller traps gave significant reductions in the numbers of adult thrips in flowers, as well as improved fruit quality.

Alongside this, thrips larvae can be controlled with the predatory mite Amblyseius cucumeris, which can be used in tunnels and open field crops as well as glasshouses. AmblyLine cu sachets from Syngenta Bioline provide a continuous supply of mites over several weeks and will also control populations of tarsonemid mites, another major soft-fruit pest.

Wider uses for existing controls

Bayer CropScience, meanwhile, has also been developing biological controls for strawberries and is finding new uses for Serenade ASO, a strain of the bacterium Bacillus subtilis that serves as a fungicide. Product manager for biologicals Tim Lacey says: "Although it is key to Botrytis IPM programmes, we're seeing very useful activity against powdery mildew in strawberries.

"It's also showing potential to limit the spread of fireblight in pears and lab studies have found it to be highly effective at controlling Phomopsis in blackcurrants. In cherries it's shown promising reductions in Monolinia and fruit-splitting issues, and in the rapidly expanding sector of UK viticulture it's finding a clear IPM role in Botrytis, sour rot and powdery mildew control."

Bayer also has several new biological products under development including a fungicide with activity on mildews and two soil-applied nematicides targeting free-living nematodes. For problem insects, foliar products are being developed to control sucking pests, especially aphids, whitefly, mite and thrips. Pheromone-based controls are showing "strong potential" against codling and tortrix moths as well as spotted-wing drosophila. Their launch is "likely to be within the next two-to-four years, given smooth progress through the regulatory process", Lacey adds.

Reducing the susceptibility of plants

Another approach is to reduce plants' susceptibility to pest and diseases by supplementing their nutrition. Engage Agro Europe used Fruit Focus to launch Sion, a nutrient for foliar and irrigated application to increase the strength, growth and health of crops. With a unique form of silicon, it boosts the development and integrity of plant cells, and can also increase nutrient activity, alleviate abiotic and biotic stresses, and increase plants' resistance to pathogenic pressure.

Levy body AHDB Horticulture, meanwhile, used the Fruit Focus event to explain how its studentship scheme is addressing growers' real-world needs while also encouraging new scientists to enter horticultural research. Two East Malling Research (EMR) PhD students are currently being funded. Working jointly through EMR and the University of Nottingham, Amy Lowe is investigating the use of hyperspectral imaging to identify differences in growth in glasshouse-based strawberry crops, so providing early warning of the onset of stress before it becomes evident to the human eye.

Benjamin Langendorf is investigating how the pre-colonisation of strawberry runners and tray plants with arbuscular mycorrhizal fungi can control Verticillium wilt. This could then serve as an alternative to traditional crop-protection products or field fumigation.

In vegetables, brassica growers, particularly in the north of the UK, are being affected by the growing area given over to oilseed rape, where the widespread use of triazoles has led to the same fungicide resistance found in brassicas, necessitating more sophisticated control measures, according to Professor Roy Kennedy of the University of Worcester.

Light leaf spot in oilseed rape is caused by the fungus Pyrenopeziza brassicae, which can be transmitted from rape stubble and crop debris to brassica crops, he explains. "Growers are now adopting a more integrated approach to disease control, starting with the use of resistant varieties and applying a broader range of fungicides at the right time. Spray timing is very important because most fungicides are protectant."

Kennedy and colleagues have developed a diagnostic tool to monitor ascospore production of light leaf spot in the air, to which growers can subscribe. "Now they can have their own lateral flow devices in their own fields to get even more precise application criteria," he says. "They schedule their fungicide timing to hit the peak of disease activity and this gives better levels of control."

He suggests timed application of Signum (boscalid and pyraclostrobin), saying: "Since more precise application of better fungicides such as Signum is now possible, growers are able to supply the right amount of crop in a sustainable way."

These should be timed to hit the three peaks of spore production of light leaf spot, he adds. "Brussels sprouts are normally planted around May and harvested the following January to March. The first wave of light leaf spot attack from nearby oilseed rape comes in July. The second peak is usually the end of August or start of September and the third in October to December, depending on weather conditions. So the crop can be under attack for the entire time it is in the ground. Fungicides need to be applied well before the crop is actually infected. Once the disease is in the crop, it's too late."

BASF field vegetable product manager Robert Storer says disease monitoring and fungicide timing are important for the successful control of light leaf spot in Brussels sprouts and other brassicas. "As part of an anti-resistance strategy, Signum should be alternated with other fungicides that work in a different way," he adds. "The overuse of triazoles in rape means that there is already widespread resistance to this group of fungicides in brassicas."

Pressure mounts for restriction on use of herbicide

On herbicides, pressure is growing for restrictions on the use of glyphosate, the use of which in UK farming has risen fourfold over the past 20 years, according to Government figures.

In March this year, the World Health Organization's International Agency for Research on Cancer (IARC) described the chemical as "probably carcinogenic in humans", leading to limitations on its use in various countries.

Retailers in Switzerland and Germany subsequently withdrew glyphosate products and German states called for an EU-wide ban, while the Danish Working Environment Authority has declared it as a carcinogen and El Salvador and Sri Lanka have already banned its use.

But the IARC findings contradicted a systematic review by the German Institute for Risk Assessment last year as part of the European Food Standard Agency's review process.

It declared that "no classification and labelling for (glyphosate's) carcinogenicity is warranted".

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