Grass-weeds within crops are thought to be the primary source of ergot infection
Management guidelines for ergot are to be updated following a surge in the prevalence of ergot in UK grain supplied for processing in recent years.
This increase has coincided with a reduction of ergot sclerotia limits in the European Union from 0.05% to 0.02% in unprocessed grain, together with the setting of maximum limits for alkaloids in processed cereal products.
These limits came into effect on January 1, 2022, just after the UK left the EU, and were not carried into British law. However, given the difficulties in segregating flour and other processed cereal products, many processors continue to set specifications in line with the EU, says Joe Brennan, head of technical and regulatory affairs at UK Flour Millers.
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While ergot sclerotia can be cleaned out of grain, it is difficult to control contamination with alkaloids, he says.
"The limit in white flour is 100 parts per billion (ppb), which may sound like a lot, but it's not at all when you consider that the average ergot sclerotia contains 1.9 million parts per billion of alkaloids," says Mr Brennan.
To further add to the challenge facing the grain sector, the 100ppb limit is set to be halved to 50ppb in 2028, he adds.
Many mills have a zero tolerance for overall sclerotia, adds Mr Brennan, and most have a tolerance set well below 0.02%.
"Since 2021 there has been a massive investment in grain cleaning, by farmers, by merchants and by cereal processers. But despite that, we are seeing very high average levels of ergot alkaloids in wheat accepted into flour mills," says Mr Brennan.
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How ergot alkaloids are transferred to grain is not fully understood, but AHDB-funded research conducted by Niab found one route is transfer in dust when grain is moved.
"When you tumble or disturb a pile of grain containing sclerotia pieces, even after cleaning you still get elevated levels of alkaloids in that grain, which suggests that there could be a friction effect, or it could be the sclerotia fragmenting into tiny fragments," says Mr Brennan.
Research has also found that ergot alkaloids can be found in healthy grain above and below ergot infection sites in the grain ear.
Niab research programme leader Dr Lesley Boyd says: "We have evidence that clean seed, developing in the ear, can contain alkaloids. We know that ergot alkaloids can move from an infected flower onto a healthy grain developing within that ear."
These are particularly challenging forms of contamination because they are invisible to a mill intake, adds Mr Brennan.
The fallback is to rely on as strict a tolerance for ergot at intake as possible, and tackling ergot at source on-farm will be important, he says.
This message is underlined by Dr Boyd, who highlights research showing that the ergots found on black-grass, Italian ryegrass and perennial ryegrass are particularly good at infecting wheat.
Grass-weeds within crops are thought to be the primary source of ergot infection, with ergot spores held in honeydew which spreads between weeds and crops transferring infection.
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In terms of physical transfer of alkaloids from ergot sclerotia to grain, researchers found that more alkaloids are transferred where damaged sclerotia are present, compared to when sclerotia are whole, adds Dr Boyd. However, alkaloid levels resulting from physical transfer were lower than those seen with transfer within the plant.
"Which is worrying, because even if we get a load of grain and clean out the sclerotia, we are not ruling out the fact that that grain is already contaminated. We just haven't seen it because it's been contaminated on the plant while it is growing in the field.
"The take-home message is that if we are going to get on top of ergot alkaloids, we've got to do it on-farm," says Dr Boyd.
For more information on ergot go to ahdb.org.uk
Ergot at a glance
- Ergot – a fungal disease affecting cereals and grasses
- Ergot sclerotia – produced by plants infected with ergot. A mass of dormant fungi containing ergot alkaloids
- Ergot alkaloids – the mycotoxins within ergot sclerotia and ergot-infected grain
Source: J Brennan/UK Flour Millers
Ergot control measures on-farm
- Effective grass-weed control for a minimum of two years can help minimise the ergot risk
- Control ergot inoculum in the field with deep tillage after harvest followed by shallow tillage in the following year
- Use ergot-free seed
- Adapt the rotation to avoid growing cereals for at least two years
- Harvest ergot-infested areas separately
Source: Niab/Arvalis
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