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From the field: Managing mycotoxins

December 6, 2017

It is hard to believe that it is that time of year again: The combines are rolling and farmers across Canada, where I am based, are starting to pack, or have just finished packing, their bunks and silos. To better prepare producers — both livestock and grain farms — for next year’s growing season, I had the chance to discuss managing mycotoxins from the field with Dr. Art Schaafsma, a researcher at the University of Guelph, Ridgetown Campus.

Tell us a little bit about yourself and your work.

My name is Dr. Art Schaafsma, and I am a researcher at the University of Guelph, Ridgetown Campus. I have a Ph.D. in crop protection and have been involved with field crop pest management at Ridgetown for just over 30 years. My main area of emphasis and research has been mycotoxins in both corn and wheat. I look at agronomic practices, sampling, detection and how to deal with mycotoxins along the value chain.

Is there a way to mitigate the risk of mycotoxins from the field, whether during planting, growing or harvesting? If so, how?

Mycotoxins are really complicated to manage, and it takes a multi-faceted approach and several tools to address them.

The typical rotation after wheat is corn, and wheat does not seem to be as large a source of inoculum as corn is. This is seen often in minimum till and no-till systems, as there is a lot of corn residue left.

Some pork producers use wheat as a way to manage mycotoxins. They will grow both corn and wheat and hope that one of those crops is clean and mix them if one is not as clean. They prefer corn, but if it is a bad year, then they will sell the wheat.

Also, pay attention to hybrid selection and look for hybrids that are less susceptible to mycotoxins. You want to look for a hybrid that will mature on time, because if you push the hybrid, you can increase the risk of mycotoxins forming. In wheat, it is much the same when it comes to variety selection.

During flowering in both corn and wheat is when the crop is most susceptible to the fungi that produce mycotoxins. In order to help combat this, producers should use a fungicide spray. The only group that is available are the triazoles to control Fusarium on both corn and wheat, and it is very important to get the timing right and get good coverage.

In corn, it is important to control western bean cutworm and other pests that can contribute to furthering the risk of mycotoxin contamination.

When it comes to harvest, some producers have started to take their wheat or corn off as soon as it can be taken off so that they can then dry it. This helps because they can control how fast the grain dries to stop the infection.

During the growing season, what are some visible signs of mycotoxin contamination?

In wheat, it is a bit easier to see the signs of deoxynivalenol (DON) because you look for head blight symptoms. These symptoms include the spikelets looking bleached. In corn, however, it is a bit more difficult, because there are a number of different species of Fusarium, and a lot don’t produce mycotoxins.

The main mycotoxin we deal with is DON. You can tell if you have DON if you have white mold accompanied by a purple or pink color anywhere on the cob. It is always better to test the grain, especially if you see any pink or purple color or white mold. Green molds and black molds are not associated with mycotoxins.

Many people worry about toxins increasing during storage; however, DON won’t increase if corn is stored below 18 percent moisture. However, this is when the mycotoxin zearalenone can be produced. Zearalenone is a late-season toxin, and there is an increased risk of zearalenone if the crop is late to harvest, stored incorrectly or not dried quickly enough. DON needs warm conditions to keep growing.  Zearalenone can form under cooler and damper conditions.

Are there certain types of mycotoxins that become more prevalent based on the type of growing season? For example, if it is a very wet year, do you see more DON versus in a dry year?

Depending on the type of year you may be experiencing, you could get different types of mycotoxins contaminating your corn or wheat. For example, DON forms in a moderately warm temperature, with its optimum temperature being 28 degrees Celsius, and if there is a lot of rain, DON can become a big issue. Also, in August, when we sometimes get the foggy mornings and then the rest of the day is warm, DON can be an issue.

DON is a complicated type of toxin and has several forms.  Most producers tend to use an ELISA test to test for DON in their crops, but it only measures a few forms of DON, not all its forms.  The other forms are just as toxic as DON.  DON can sometimes also be masked or hidden. This happens when DON is conjugated with a sugar and is then overlooked by an ELISA test. This is why sometimes you may run an ELISA test, think there are no problems, then discover a mycotoxin.

Fumonisin, another type of mycotoxin, shows up when there is heat stress, with low- to mid-30s degree Celsius weather and drought. In Ontario, we do not get this one too much because it isn’t hot and dry enough.

Zearalenone does not show up in wheat because it is too warm during flowering, as wheat heads out in June or July. However, it does show up in corn in the fall.

One toxin producers should be aware of is T-2 toxin. T-2 is related to a late harvest, and we find it regularly in corn that is left in the field too long and when corn lodges. The danger with this one is that it is 10 times more toxic than DON.

Where do you think the next advancements will come from in reducing/protecting against Fusarium-produced mycotoxins?

In corn, we are working on a sustainable way to manage western bean cutworm. I would like for there to be an incentive for farmers to grow less susceptible hybrids. This may happen soon because other end markets that buy a lot of corn are getting frustrated by mycotoxins as well. It is not just livestock producers that should be looking at their corn this way. More often now, there is a penalty applied for how much DON is brought into the processing plant. Awareness is growing and will lead us to change.

In wheat, the industry continues to improve the genetics. There is more progress in managing mycotoxins in wheat than in corn. We can manage it reasonably well in wheat. 



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