Beet moth threat: What farmers can do to mitigate risk

Beet moth has jumped up the risk agenda for sugar beet growers, as the 2025 sugar beet season marked a shift from isolated cases to economically damaging infestations in parts of the British beet area.

British Beet Research Organisation (BBRO) crop protection lead Prof Mark Stevens told agronomists at the recent Association of Independent Crop Consultants (AICC) conference that the industry is now dealing with a pest that is here to stay.

“Unfortunately, I think it’s established itself and it’s one that we’re going to have to keep a very close eye on going forward,” he warned.

See also: Suffolk beet grower counts huge cost of beet moth

What happened in 2025?

Mark said that although beet moth was first noticed in UK crops in 2020, last season was the first time it became widespread and severe in places.

Damage was most evident during prolonged warm and dry spells, particularly on lighter, drought-prone soils, where crop stress allowed moths easier access to the beet crown.

“The worst impacts went hand-in-hand with drought conditions.

“Where crops collapsed and the canopy opened up, adults were easily able to get in, reproduce, lay eggs and continue reproducing right through the summer.”

In some badly affected fields, larval numbers reached extreme levels.

“We were finding 50-60 caterpillars per plant in some samples,” Mark recalled.

Feeding damage leads to black heart, frass accumulation, secondary infection and, in some cases, total defoliation.

Geographically, pressure appeared greatest in parts of East Anglia, particularly along the A14 corridor from Bury St Edmunds through Newmarket and Cambridge, before spreading northwards where dry conditions persisted.

Crucially, the pest did not behave as recorded in older literature, highlighting the need for up-to-date information for growers and agronomists.

“If you read the textbooks, they talk about two migration periods separated by six to 10 weeks. That’s not accurate.

“Once they started, every week you had another flush.

“Overlapping populations put a lot of pressure on any [insecticide] product you’re trying to use.”

How growers responded

An audience poll during the conference workshop session showed that about 60% of agronomists recommended an insecticide on at least one crop for beet moth control in 2025.

Of those, almost half relied on pyrethroids, while only a small proportion used the emergency-authorised diamide product Coragen (chlorantraniliprole), largely due to cost.

Mark acknowledged why decisions fell that way, but urged caution.

“I get very nervous about pyrethroid use late in the season, particularly in August and September, when you’ve got beneficials and aphids building for the following season.

“The last thing you want to do is remove those beneficials and create problems for the next crop.”

Lessons for 2026

Looking ahead, the message for 2026 is clear: beet moth needs to be managed with an integrated pest management (IPM) strategy, not tackled with reactive sprays once damage is obvious.

“There are no UK thresholds at the moment. The French use 10% of plants showing damage, but I’d argue that’s probably too late, given what we now know.”

Instead, he stressed the importance of early canopy development and reducing crop stress.

“Early sowing to get that canopy up, and water where it’s available, are important.

“The canopy is a physical barrier, and where heavy rain kept canopies intact in 2025, we saw far less impact.”

Monitoring will also play a bigger role in 2026, with pheromone traps and artificial intelligence-enabled monitoring systems being rolled out to provide earlier warnings of adult activity.

“There’s no point monitoring if we’re not getting that information out quickly,” Mark said.

Carryover risk is another concern, and if beet moth is protected in the crown or petioles, it can survive very cold temperatures.

“So, hygiene and how we manage residues really matter,” he added.

While further emergency approvals and new chemistry may emerge, Mark urged growers not to rely on product solutions alone.

It requires an IPM strategy including canopy management, variety choice, stress reduction and careful pest and crop monitoring.

“If we get another prolonged drought, everything is going to have to come into play to keep on top of it.”

Agronomist’s view – Tim Martin, AICC/Apex Agronomy

Tim Martin © AICC

Suffolk-based Tim Martin has been aware of beet moth across his area for several seasons, but 2025 was the year that it turned into a major issue, particularly on light, Breckland soils.

“Where beet was already under drought stress, it tipped crops over the edge.

“In severe cases, complete defoliation occurred in some areas within crops by mid-September, and yield loss would have been 30-35%.”

Looking ahead to the new campaign, Tim repeated the importance of good establishment and early canopy development.

Alleviating compaction, supporting rooting depth, and maintaining moisture where possible all help reduce water stress and allow crops grow away from damage.

Irrigation plays a clear role in limiting impact and should be utilised where available and feasible.

Tim also believes cultivation strategy deserves consideration where beet moth pressure was high in 2025, with the moth able to overwinter both as pupae and larvae in beet crowns.

“By ploughing them deep into the soil, you make emergence more difficult in spring.

“Evidence is still limited, but it’s a pragmatic step where problems have been severe.”

Insecticides remain a tool of last resort, but experience in 2025 showed they can have a place, added Tim.

Across his area, Coragen delivered better results than initially expected from early post-application assessments, with treated crops finishing in visibly better condition.

Timing remains the greatest challenge to acceptable control, making British Beet Research Organisation monitoring data vital for the season ahead.

“Ideally, you would target adults, but that’s very difficult.

“Larvae feeding on treated leaves can be controlled, but spraying when larvae are small and before they are deep in crowns is crucial.

“Essentially, it comes down to monitoring conditions and carrying out a risk assessment.

“If the season is wet, there may be no problem or need to spray, but if it’s dry again then action may be required.”