Mycotoxins look like being an annual issue. Lucy de la
Pasture finds out how the grain train coped last year and what it
means for growers this season.
The Miller's Tale
Challenging, that's how Martin Savage, Trade Policy Manager for
the National
Association of British and Irish Millers (NABIM), describes
their experience of grain from the 2008 harvest.
Alarm bells rang early in the season as sample results from
mills arrived at NABIM. These showed about 10% of samples were
exceeding deoxynivalenol (DON) limits (compared with 7% in 2007).
But the real cause for concern was that background levels were
high, indicating
mycotoxins were present
in most samples, though not exceeding limits.
"The harvesting period was long and protracted because of the
wet conditions." says Mr Savage. "This gave us problems with DON
and zearalenone (ZON), mycotoxins produced in the field by fusarium
fungi."
A further complication of the difficult harvest, particularly
for growers that market grain from May to July, is an increasing
risk of ochratoxin A, a mycotoxin which can develop on moist grain
during storage. "So if grain has been stored at high moisture
levels or has developed a taint or smell, don't offer it to
millers," he warns.
In the three years since
EU legislation was introduced limiting the levels of DON and
ZON mycotoxins in grain, the whole grain chain has been learning
rapidly. And setting a legal limit is not all the legislation has
done. "Growers have become responsible for food safety on raw wheat
for the first time," says Mr Savage.
Since DON testing became mandatory, carrying out a risk
assessment has been an essential part of the marketing process. But
as intakes at mills progressed last winter and rejections became
commonplace, it became clear that the risk assessment wasn't
working, he says.
"In February we had to introduce a system of rapid DON test
counts to accompany consignments of grain, which although more cost
to the farmer, reduced rejections and made the system more
workable."
Breakfast cereals scarce
If the millers had it bad, the breakfast cereal manufactures had
an even harder job sourcing grain that didn't exceed legal
mycotoxin limits, says
Weetabix's Keith Turnbull.
They introduced rapid DON testing as early as November to make sure
grain was on spec.
"The way the EU regulations are set up, the limits get tighter
as you go down through the food chain," says Mr Turnbull. "Where
the limit for raw wheat is 1250ppb, for breakfast cereals the limit
is just 500ppb."
And because mycotoxins are mostly in the bran, the main source
of fibre in breakfast cereals, and they are further concentrated as
the cereal is dried to a moisture content of 5%, grain needs to be
lower than the legal limits for mycotoxins at intake.
"Once we had the DON situation under control, we identified
issues with ZON for the first time," says Mr Turnbull. "ZON
appeared late and was a problem in raw material supply, but now
testing is in place for this as well."
It seems that the rapid testing will be here to stay, at least
until the picture for harvest 2009 has been established, believes
Mr Turnbull. "But now the industry is set up to manage an
exceptionally bad season for mycotoxins, the whole grain chain has
the opportunity to learn from it, make British farming as safe as
possible, manage the risk in the crop and come out stronger than
before."
Grain traders' troubles
From the grain traders' perspective last season was a year of
complications, says
Frontier's head of wheat trading, Simon Christensen. Changing
requirements from the milling and starch trade brought confusion
with risk assessments and DON measurements for a short while.
Grain traders had contamination issues at intake after
last harvest
There were issues at intake, rejections and problems with
sampling, an area which is being looked at closely by The Mycotoxin
Stakeholder Group, which is working to find a better sampling
regime. One of the problems with mycotoxins is that they don't
occur in a homogenous way, one load can be high and another low and
they've come from the same field.
"But the message about the importance of mycotoxins has been
understood by farmers, and the supply chain will be more able to
cope if it happens again," Mr Christensen says. "Sampling remains
an area of concern from the grower's perspective. They need to be
confident that the tests carried out at intake are accurate and
that the wheat being imported also follows the same requirements
from a testing and sampling regime to ensure a level playing field
exists with their foreign counterparts."
In the field
So why was last season so bad? Simon Edwards, fusarium expert at
Harper Adams explains
why the risk assessment may not have worked and how the mycotoxins
occur.
"The
HGCA risk assessment was based on data from 2001 to 2007 and
during this time, average rainfall in the pre-harvest period was
20mm. Last year actual rainfall was in the region of 100mm, with a
substantial delay to harvest because of the wet weather in August
and September. None of this was factored in the model," says Dr
Edwards. "For this season, the risk assessment will be revised to
take these factors into account and enable growers to identify
fields at particular risk which may then require testing."
Last year was also the first time ZON mycotoxin was a real
problem. "It has a lower limit and is only produced as the crop
ripens, whereas in contrast DON is produced from infection at
flowering," says Dr Edwards. "Any delay in harvest has an impact on
ZON levels and this was clearly seen last harvest when more samples
exceeded the limit for ZON (29%) than DON (13%). Many high ZON
samples don't make milling spec as they have low hagbergs and
specific weight, so are effectively 'screened' out of the milling
process and are less of an issue at mill intake."
And what is the likelihood of a repeat this season? The bad news
is there is a higher risk of fusarium infection than normal because
there is more inoculum around as a result of high levels of
fusarium head blight (FHB) last harvest. The good news is that,
although the potential for a problem is there, actual rainfall
during flowering (GS61-65) and pre-harvest will determine the
severity of FHB, so mycotoxins issues may not occur.
"The main source of inoculum is crop debris, so crops are at
greater risk following minimal cultivations and maize," says Dr
Edwards. "Late sowing also increases the risk of fusarium and many
crops were late sown last season, crops following potatoes also
seem more vulnerable to FHB."
T3 decisions
So what should growers do? Consider the risks, especially
predicted rainfall for the flowering period before making T3
decisions, advises Dr Edwards. "In commercial trials last year,
where robust T3 fungicides were applied there were significant
reductions in fusarium infection (50-70%). Even so, some samples
still exceeded legal mycotoxin limits."
In the UK levels of FHB in the crop, typically pinkish bleached
ears, doesn't necessarily correspond to levels of mycotoxins
present on the grain. This is because it is only the true fusarium
spp that produce mycotoxins, and FHB can be caused by Microdochium
nivale and M. majus, neither of which produce mycotoxins. Of the
five common fusarium species, F. gramineaum and F. culmorum are the
most significant in terms of DON and ZON production.
A robust fungicide treatment at T3 can keep FHB at a low level
and reduce the risk of mycotoxins occurring. But fungicide
selection is important because only fungicides for fusarium control
that contain triazoles or new approval Topsin WG
(thiophanate-methyl), will control the true fusarium species
responsible for mycotoxin production. And of these actives only
those containing prothioconzole, bromuconazole and
thiophanate-methyl have a label registration for actual DON
reduction. While strobilurin chemistry has excellent activity on
Microdochium species, it doesn't control true fusarium with the
exception of dimoxystrobin.
Agronomist Tom Scotson, Procam, says that whereas T3 decisions
used to be a top-up for septoria and rust control, things have
definitely changed. "Concerns with DON levels, especially in
milling wheat and breakfast cereals, means that we must have a
planned strategy to control fusarium pre-flowering."
Using programmes based predominantly on prothioconazole, the
standard for fusarium control, he describes thiophanate-methyl as a
useful addition to the armoury, having a different mode of action
to the triazoles.
Trials work carried out by
Certis with
thiophanate-methyl, emphasizes the importance of correct timing for
optimum fusarium control, with the period from the beginning of
anthesis (GS61) to mid-flowering (GS65) giving the greatest
reduction in fusarium levels on the ear.
Grain chain
- Challenging season for millers in 2008
- Breakfast cereal firms had trouble with mycotoxin limits
- Complications for grain traders
- Risk assessment proved inadequate
- Consider risks before making T3 decisions this season