The dwindling availability of insecticide seed treatment and nematicides has paved the way for pest control using entomopathogenic nematodes.

Following successful trial work in key high-value crops, farmer uptake looks set to increase.

Insecticide use has taken a battering in recent years due to environmental concerns, and many active substances – including the pyrethroid insecticide seed treatment tefluthrin – are no longer available.

The loss of conventional products always has consequences in the field, and growers must quickly adapt.

See also: Wireworm in potatoes is worsening – how growers can tackle it

Problem fly species

Tefluthrin’s loss has made it particularly challenging to control a group of closely related fly pests affecting a range of high-value crops.

This group includes bean seed flies (there are two species of concern), onion flies, cabbage root flies, and carrot flies.

Another loss forcing growers to adapt is the withdrawal of Mocap, an ethoprophos-containing granular insecticide that helped potato growers reduce damage caused by wireworm (click beetle larvae).

With growers desperately needing tools to manage these pests, researchers and commercial companies have been testing a variety of non-chemical methods or products to provide reassurance.

One such company is Koppert, which was founded in the Netherlands in the late 1960s.

Its products are now an integral part of integrated pest management (IPM) programmes in protected vegetable and fruit crops under glass.

Koppert UK’s market development and technical consultant Dr Richard Binks says the firm has been screening its solutions against key pests controlled by lost or threatened conventional chemistry over the past decade.

Helpful nematodes

The company is one of the largest producers of entomopathogenic nematodes in the world.

Testing at its Rotterdam headquarters revealed that certain species have been effective against wireworm.

Steinernema carpocapsae occurs naturally in the soil.

It was discovered that once these microscopic organisms enter a wireworm through its breathing tubes, mouth, or anus, they secrete a substance that induces sepsis and ultimately results in death.

“Wireworm isn’t just a UK problem; it’s a worldwide issue – and once we confirmed that these nematodes offered good efficacy in the lab, we took them outside for field trials.

“Initially, that was in Italy – applied through drip irrigation – and some very positive results were achieved.

“Those results have been replicated in other countries, including Germany and France,” explains Richard.

As reports of wireworm damage to potato crops became more frequent and severe, Koppert’s nematode product Casea attracted interest in the UK.

Casea contains the Steinernema carpocapsae species in an inert, biodegradable gel carrier –

Koppert has collaborated with a handful of agronomy and grower groups to trial the product here, including independent potato specialist James Klug of Deben Agronomy, a group overseeing potato crops across East Anglia.

About 95% of James’ advised potato area is in East Suffolk and destined for the pre-pack market, which has very low tolerance to wireworm damage on tubers.

This means wireworm has arguably become his number-one enemy since Mocap’s withdrawal.

“To be fair to packers, they have slightly increased tolerances due to the challenges we face, but there is only so much our consumers will accept before it starts hurting demand,” he explains.

Replicated trials

With current nematicides having little impact on wireworm populations, James and his colleagues have been seeking alternatives.

They discovered the potential of Koppert’s nematodes through the Vegetable Consultants Association (VCA).

To investigate further, he set up fully replicated trials in 2024 on a Suffolk sandy loam site with a wireworm population.

Wireworm was identified through bait trapping in the months before the trial was established.

Treatments included an untreated control, Capyphor (Heterorhabditis bacteriophora), and Casea.

Dose response was also investigated by applying each treatment at both a high and low rate (1bn/ha versus 2bn/ha).

A programmed approach was taken in the trial, with three applications deployed at tuber initiation, during rapid canopy growth ahead of rows closing over, and again shortly after haulm destruction.

With multiple species at different stages of their lifecycle in the soil, each potentially active at different times, it was hoped that the three sprays would increase the chances of a positive outcome.

A higher water rate and soil moisture are also key in maximising efficacy.

Some flexibility regarding application timing was required to ensure nematodes were applied just ahead of rainfall or irrigation.

James says wireworm pressure wasn’t as high as expected from trapping results.

However, at 5% damage in the untreated, it was still high enough to be economically destructive in a wider commercial crop.

“We found three treatments of Casea at 2bn/ha reduced that 5% to 0%, and this was a statistically significant result, representing a considerable return on investment if it was in a commercial situation.”

James does caution that it is only one year’s experience, but he would already consider using a nematode product commercially due to the stark lack of alternatives.

“The results exceeded my expectations and are very promising.

“We have some data to support this now and, although more work needs to be done, I would consider using nematodes where we know there’s high pressure,” he adds.

Fly larvae

Another encouraging nematode species is Steinernema feltiae, which is contained in the product Capirel.

It demonstrates promising activity against bean seed fly, onion fly, cabbage root fly, and carrot fly.

Agronomy group Hutchinsons’ fresh produce manager, Dr Tim Lacey, says the firm has been acutely aware of the gaps left by conventional chemistry in many speciality crops.

Finding a tool against these pests has been a key driver of its partnership with Koppert.

Bean seed fly has been the priority, being a widespread issue that affects a range of crops, including peas, beans, alliums, cereals, vegetable brassicas, and maize.

Although its distribution is widespread, damage tends to be localised and sporadic.

However, because the larvae of the flies feed on freshly drilled seeds just before or as they germinate –  and in the early stages post emergence – consequences can be severe.

In the worst case, total crop loss is experienced.

Green beans and vining peas

This is particularly critical in green bean and vining pea crops, which tend to be drilled later in the spring than combinable peas and beans, leading to a much higher potential for damage.

“We’ve been working with one of the largest fresh green bean growers in the UK to test and trial the concept, and actually use it in a realistic commercial situation as well,” says Tim.

Capirel has been applied in-furrow at drilling, ensuring the dose is delivered exactly where it is needed – especially in the soil covering the seed.

Using it this way also allows growers to reduce the dose relative to an overall spray, which makes the application even more economically viable, Tim says.

“They are also in the soil right away, so they are somewhat protected from drying out and the UV radiation that can cause desiccation of the nematodes if applied on the surface.

“Good levels of control of bean seed fly have been achieved, and the grower was satisfied sufficiently with the results, so they are planning to treat nearly all their exposed area in 2025.”

Onion fly also features on Tim’s radar and can sometimes be challenging to distinguish from bean seed fly.

Both are a significant issue in onions and leeks in the UK, especially since the loss of Force (tefluthrin) seed treatment authorisation in these crops.

Emergency authorisations for Force treated seed with a restricted dose and limitations on area have only provided partial control of bean seed fly and onion fly in onions in 2024.

“In the Netherlands, where both are a serious problem, Capirel nematodes are successfully being used to reduce damage over large areas, with even more being planned for 2025.

“UK growers have an increasing interest in following suit,” says Tim.

Cost-effective

Using Capirel costs a little more than the preceding or alternative chemical options.

However, Tim believes the return on investment in high value crops like green beans or even onions still stacks up – especially when compared to having no solution at all.

The Processors and Growers Research Organisation (PGRO) principal technical officer, Becky Ward, agrees there is potential when using nematodes in green beans.

This potential could extend into the 35,000ha of vining peas grown in the UK each year.

PGRO’s research has shown significant reductions in damage using nematodes when weather conditions are suitable for application—when rainfall occurs at or just after spraying—at both plot and field scale.

However, Becky emphasises that nematodes need to be part of an integrated pest management plan that incorporates other tactics proven effective against bean seed flies since the loss of key seed treatments.

Crop establishment practices and timing are crucial.

Crops drilled into seed-beds prepared the same day are at much greater risk than those where seed-beds are prepared 7-14 days in advance of planting.

PGRO has jointly sponsored a PhD student at Warwick University, who has produced a bean seed fly risk model.

This model will help predict when the pest will be at its worst in specific areas and is set to be validated in 2025, with implementation planned for 2026.

Becky says one of the significant issues the industry now faces is that, in the past, it was possible to achieve very high levels of bean seed fly control with a straightforward application of a conventional pesticide.

“When considering biocontrol, you generally don’t get that level of control or consistency, so it’s much more about an integrated approach that includes various other techniques.

“That means slightly earlier cultivations, timing drilling to avoid the worst periods of activity, and then, with targeted use of products like nematodes, you can achieve excellent control in crops like green beans or vining peas.

“One of these strategies alone might not suffice,” she explains.

More complex

This is a point that Richard is keen to stress to agronomists and growers using nematodes and other biocontrols: it can be more complicated and challenging to achieve optimal outcomes.

With nematode products, storage, preparation, and loading of the sprayer, as well as using the right temperature of water and tank mix partners, are all crucial factors in achieving the best levels of control.

It is also vital to understand the impact of using other crop protection products in mixed programmes.

To assist with this, Koppert has developed an app that offers risk assessments for chemicals that might be used in the glasshouse or field alongside biocontrols.

“We also advise growers on the best conditions for application. Using them early in the morning or later in the day when UV levels are low is most effective.

“Most spraying systems on farms are suitable for applying nematodes, as they are robust and can tolerate pressures up to 20 bar.

“However, we recommend removing any filters with mesh finer than 0.3 mm to avoid clogging,” Richard advises.

Key nematode products
Product	Species	Target(s)
Casea	Steinernema carpocapsae	Various insect pests in stone fruits, outdoor vegetables and urban trees
Capyphor	Heterorhabditis bacteriophora	Weevils and other beetles in a wide range of crops
Capirel	Steinernema feltiae	Various insect pests in orchards, berries, outdoor vegetables and urban trees
Source: Koppert