Mycotoxins remain, perhaps, a misunderstood threat for growers. Certainly there is some confusion about how big a threat they pose, what causes them, and how to minimise risk.

That comes across in a survey conducted for Bayer CropScience of 350 growers and 28 advisers.

While most growers have made the link between poor weather at flowering and mycotoxin-causing fusariums and recognise a growing threat, few growers know about the relative importance of maize in the rotation or the impact the disease can have on grain yields, says the firm’s Alison Daniels.

“CSL data suggest that Michrodochium nivale can take up to 10%, while Fusarium graminearum and culmorum can shrivel grain causing up to 30% yield loss.”

Most growers, according to the survey, attempt to control fusarium as part of a general ear disease control strategy. But Dr Daniels believes that in the future growers may need to target fusarium, and, therefore, mycotoxins, specifically in high-risk areas.

“There is scope in the market for two approaches a general purpose clean-up where fusarium risk is low, or a specific ear wash timed to minimise mycotoxins.”

The latter needs a triazole-only approach, she says. “You need a full load of a fusarium-active azole fungicide and one that will do michrodochium, too.”

Reducing the azole dose and adding a strobilurin – particularly one which doesn’t have any activity on true fusarium – can make mycotoxin risk higher, she points out. “There does seem to be some confusion over which products control true fusarium.”

For example, in the survey 39% of growers specifically mentioned Amistar (azoxystrobin) when asked about controlling the disease, she points out. “But it only controls michro-dochium, not true fusariums.”

Timing for fusarium is generally well understood – the start of flowering is ideal, Dr Daniels says. “With prothioconazole you do have a slightly wider window because of its activity.”

Anyone who thinks mycotoxins from fusarium infections are not an issue should perhaps ask the milling industry.

Just after harvest last season, in certain southern counties’ mills, one in 10 loads were being rejected for being above the legal limit of 1250ppm, according to Martin Savage, the trade policy manager for Nabim.

“It is something that shouldn’t have been happening, as it is illegal to sell it for food use.”

It prompted a wide-scale ramping up of random testing by mills and changes to the post-harvest declaration form growers need to fill in for each load.

“The mills were examining random samples from the time harvest started at the rate of one load per mill per day.

“But when nationally the mills were picking up about 5% of loads with levels over 1250ppm, we had to start sampling more intensively.

“At one point some regional mills were testing every load, which caused massive problems with queues at intake.”

Analysis of the samples revealed the problems were based mainly on geography. “Usually the coastal counties down the east and into the south from East Yorkshire to Dorset are higher risk because of their climate. But last year we found there was also an arc through the midlands from Lincolnshire to Gloucestershire where there were also problems.”

It led to an amendment of the grain passport in October, he says. A new section was added asking growers to conduct a risk assessment for fusarium mycotoxins based on an HGCA-developed protocol.

Where the assessment finds a high risk a mycotoxin (DON) test is required to confirm that the level of DON is below the legal limit before it can be sold for use in the food chain. A test is also required in 2007/08 if there is a medium risk and the grain was produced in one of the following counties: Lincolnshire, Norfolk, Cambridgeshire, Leicestershire, Northamptonshire, Warwickshire, Worcestershire, Gloucestershire, Dorset, Hampshire or Sussex.

The risk assessment is straightforward, according to Roger Williams, assistant research director at the HGCA. “It was originally developed to help growers assess what agronomic measures they might need to take [to reduce mycotoxins] from cultivation right through to T3s.”

That means starting the risk assessment now and using it as a tool to help decide on whether a T3 fusarium spray is necessary is a good plan, he says. “Use it as a tool to help minimise risk rather than view it as another necessary piece of bureaucracy.”

A few tweaks to the assessment for this season are just about to be released, Dr Williams adds. “At the moment it is not in a logical order so that will be changed, but more importantly, the cultivation assessment is currently very black or white – either ploughing or not. There is some evidence that the degree of mixing of the soil is important to risk.”

More guidance will also be given on what high, moderate and low rainfall really means, he adds.

Adopting the risk assessment cut rejections to grain mills markedly, Mr Savage says. Rejections for the season totalled just 0.22% of all loads. “It meant those loads simply weren’t sent. The passport was key to sorting out the issue.”

Top rejection issues were low Hagbergs at 0.6%, while 0.4% failed for poor visual appearance, and 0.35% for proteins, moisture content or specific weight.

“It could have been worse [for mycotoxins],” he points out. “Last year was only a medium year – we had prolonged flowering with a wet period at the end.”

Useful links

• CSL
  
• Food Standards Agency
  
• HGCA