Careful grain sampling key when looking for mycotoxins

Ontario’s worst-ever year for DON infection in corn may provide some guidance for managing the problem in Western Canada

For Ontario corn growers dealing with an outbreak of deoxynivalenol (DON), 2018 was a year to forget.

“It was a really major, widespread issue,” says Art Schaafsma, a professor in field crop pest management for the University of Guelph’s Ridgetown Campus. He says the last time the industry saw widespread issues with DON was in 2006 when producers were shocked to find contamination levels up to 10 parts per million (ppm). But in 2018, some producers saw levels of over 50 ppm. “The whole industry was up in arms about what to do with all this corn.”

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Except for the DON contamination it was a high-quality crop, and most went to ethanol plants, with some byproducts reaching western Canadian feedlots.

Mycotoxin contamination poses challenges for the industry because the toxin doesn’t break down, but accumulates in byproducts.

Across Canada, DON is still the most economically significant mycotoxin. It can occur across all grain types and is associated with infection by Fusarium graminearum, the pathogen that causes fusarium head blight (FHB) in wheat and gibberella or fusarium ear rot in corn.

Higher-yielding corn hybrids tend to be more susceptible to DON contamination, and conditions that are ideal for corn are also ideal for toxin development, Schaafsma says.

“Years ago we’d have sporadic problems with DON. Every once in a while we’d have a larger outbreak. But yield is king, and the outbreaks are becoming more frequent and they’re hitting harder all the time.”

Oats and barley research

In Western Canada, fusarium is less of an issue, but there’s little room for complacency.

Sheryl Tittlemier, a research scientist at the Canadian Grain Commission’s Grain Research Laboratory, says the CGC annually analyzes samples of wheat, oats and barley for its cargo-monitoring program, as well as samples from the harvest sample program. The latter are used for research in grading factors such as fusarium damage.

Two mycotoxin groups are economically relevant in Canada: fusarium mycotoxins and ergot alkaloids, which can cause issues in feed grain. Both types depend on weather during the growing season, Tittlemier says.

A third mycotoxin, ochratoxin A (OTA), doesn’t occur in the field but can become a problem in stored grain.

The CGC just wrapped up a surveillance study in milling oats in collaboration with the Prairie Oat Growers Association (POGA), comparing mycotoxin concentrations year to year.

“When we looked at the harvest samples there was a wider range of DON concentrations than in the samples we obtained from processing facilities or shipments provided by grain handlers,” Tittlemier says. “We’re not seeing high levels of DON.

“This indicates that the industry is aware of the DON and is managing what ends up in the oats that they’re using. This data is proof that management is having an effect.”

In barley, DON presents more of a problem, says Marta Izydorczyk, a research scientist and program manager for barley at CGC.

“FHB is spreading in Western Canada — initially it was just in Manitoba but we’ve started to see it in the other western provinces,” she says. “For farmers, FHB on malting barley means lower yield and the likelihood that their barley won’t be selected for malting.”

The maximum limit for DON in barley is one ppm, says Izydorczyk; malting barley with levels above this is rejected.

Fusarium has a secondary impact in malting barley: if barley with low levels of DON is selected, fusarium and other fungi can grow and proliferate during malting, producing even more DON.

In collaboration with the Brewing and Malting Barley Research Institute, the CGC is currently testing an innovative post-harvest treatment developed by a Scandinavian company called ThermoSeed. It has the potential to eliminate the pathogen during malting and brewing. The ThermoSeed process can treat up to 1,500 kg of grain per hour, and is already used commercially in Sweden, Izydorczyk says.

“The project’s objective is to determine whether the ThermoSeed process can be applied to malting barley with low pathogens and low DON levels without any negative impact on seed germination and malting quality,” she says.

A sample of last year’s crop was shipped to Sweden and has already been treated and returned, she adds. “The results are looking promising — there are definitely no negative effects on barley germination.”

Sampling protocol

Mycotoxin contamination doesn’t currently affect grade, although it affects price — Schaafsma points to discounts in Ontario corn of up to $60 per tonne for DON contamination last year. The CGC has initiated a consultation on whether DON should become an official grading factor, but Canadian elevators do test for DON if fusarium is an issue or if buyers request it.

Last year, irregular readings from corn samples at elevators left many Ontario farmers disgruntled, Schaafsma says.

In some cases a farmer would deliver a load of corn, which would be sampled and tested and given a high mycotoxin reading, and then wouldn’t be allowed to dump the load, he says. “He’d bring the same load back, it would be retested and it would be fine. There was no confidence in the testing, either for the buyer or for the seller.”

The Grain Farmers of Ontario asked Schaafsma’s team to evaluate sampling protocols to assess whether probe samples were part of the problem. Schaafsma’s team found no issues with probe sampling. Nor did they find problems with the ELISA test kits used to evaluate DON levels, but they did find problems with sub-sampling in the grading house, he says.

There, grain would be tested for grading factors, and then a small random quantity of the grain would be siphoned off and run through a mycotoxin test.

There were issues with the ways samples were being selected and ground for the test, says Schaafsma.

“Within a two-kg sample we could get numbers ranging from five to 15 depending on the quantity of grain you took from the sample. We took a number of tests to see how much variability there was and the variability was high,” he says.

Darrall Marshall, operations manager at G3 Glenlea, says there is no standard practice for mycotoxin tests at elevators in Western Canada. He says elevators follow standard formulas to sample grain. Samples go into the grading room and are tested according to CGC grading standards. Grain is ground for DON tests, but neither the tests nor the grinders are regulated for this — instead, elevators follow protocols set by grinder manufacturers.

“If it’s not done absolutely precisely, you’ll get different numbers because it’s parts per million you’re dealing with. And human error can be a factor,” Marshall says, adding. “Inconsistency in the process will lead to different results.”

Schaafsma presented his findings to an industry meeting in late August, and says some elevators have already made changes to what they’re doing.

“We’re trying to set up a standard practice so we can have more confidence in the sampling. We hope for the new crop to have something in place for corn so people don’t need to be upset,” he says.

“Sampling is so key to understanding what you have, so you can’t be too careful to get the right result,” he says. “It’s way beyond just taking a cup of grain and testing it.”

Schaafsma’s team is currently developing a sampling system farmers can use to test their grain before it leaves the farm. “It’s easy to sample dust with a vacuum while grain is being transferred, so we did some work with wheat and we’re now doing it with corn where we’re looking for a relationship between what’s in the dust and the grain,” he says.

“This would give farmers results right away, so they know if they should unload a given load or blend it off and try again.”

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Julienne Isaacs

Julienne Isaacs is a Winnipeg-based freelance writer and editor. Contact her at [email protected]

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