Grower guidelines for managing ergot are to be updated by the AHDB, following a steep rise in the incidence of the pathogen over the past three years and confirmation that grain can be contaminated with toxic alkaloids in different ways.

While the mechanism involved is not fully understood, research has shown that ergot alkaloids can be found in grain previously considered unaffected or healthy, both above and below the infection site on the ear, having moved in the plant.

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As a result, wheat that has been accepted into mills can produce flour with alkaloid levels above legal limits, posing a significant compliance challenge for the supply chain and potentially posing a food safety issue.

Invisible at intake

While the purple-black ergot sclerotia that form in the place of grain after infection has occurred are very visible and can be removed by colour sorting, other forms are effectively invisible to a mill intake.

“What the AHDB-funded research done by Niab has shown is that removing sclerotia from grain does reduce alkaloid content, but not always to zero,” says Joe Brennan, head of technical and regulatory affairs at UK Flour Millers.

One reason is that where ergot sclerotia get broken into smaller pieces, grain that is tumbled or disturbed leads to elevated alkaloid levels, he reports.

Another potential source of physical contamination is the dust or residue that arises when grain is harvested and transported.

“It’s become apparent that colour sorting for small ergot fragments and grassweed ergot may not be as effective as required and we need to understand why.

“Grain cleaning is an expense, as well as an additional task.”

Ergot limits

Joe adds that current EU limits for ergot will be halved by 2028 and as many UK companies sell flour-based products across Europe, ergot contamination is relevant to the whole supply chain.

Grassweeds can also get ergot, producing sclerotia that are smaller, thinner and more fragile than those found in wheat and which may be more prone to breakage, he suggests.

Either way, tackling ergot at source is necessary, believes Joe.

“There’s no rapid test that can be done at the mill, so this invisible ergot has to be addressed at the farm level.”

Grassweed hosts

Niab researcher Dr Lesley Boyd says ergot can be found in 37 grass species hosts, but there’s no conclusive evidence that grass margins are a source of infection.

Of the species tested, blackgrass, couch and ryegrass were found to be particularly good at re-infecting wheat.

“Grassweeds within the crop are thought to be the primary infection source, so good weed control is important in wheat destined for human or animal consumption.”

Ergot sclerotia can survive in the soil for five years, she says, meaning deep tillage after harvest is advised to bury them.

This should be followed by shallow tillage the following year.

“The risk of infection depends on the weather conditions between flag leaf and pollen shed. If it’s cool and wet at flowering, the risk increases.”

Alkaloid movement

Of greater concern is the discovery that alkaloids can move in the growing plant, so they are being transferred from infected flowers into healthy grain.

“This is different to the physical transfer that may take place in a pile of grain, and it means that grain can already be contaminated when it is harvested.”

As ergot alkaloids can contaminate grain previously considered clean, ergot management has to be focussed at the farm level, she stresses.

Sacha White, lead crop protection scientist at AHDB, says the updated ergot management guidelines will involve a review of the existing guidance and research, with the first output expected in spring.

“That will be followed by an ergot identification guide, which will be available in the autumn.”

Joe Brennan, Dr Lesley Boyd and Sacha White were speaking at the UK Cereal Pathogen Virulence Survey (UKCPVS) stakeholder meeting at Niab near Cambridge