2023 Ontario Grain Corn Ear Mould and Deoxynivalenol (DON) Mycotoxin Survey

OMAFRA field crop specialists in collaboration with Grain Farmers of Ontario (GFO) and members of the Ontario Agri-Business Association (OABA) have completed the annual Ontario corn ear mould and DON mycotoxin survey. Corn ear moulds such as Gibberella and their corresponding mycotoxins occur every year in Ontario. These mycotoxins, particularly deoxynivalenol (DON, also referred to as vomitoxin) are produced primarily by Gibberella/Fusarium ear moulds and can be disruptive when fed to livestock, especially hogs. The 2023 survey found 77% of samples tested low (<2.00 parts per million (ppm)) for DON. This is lower than the 10-year average of 88%, but better than recent higher-testing years of 2018 and 2016.  


From October 2 to October 5, 2023, 192 ear corn samples were collected from across the province. Five consecutive ears were collected from four random locations (20 ears total) throughout a field and placed into high temperature driers (80°C) as soon as possible after collection. Pictures were taken to document moulds, insect/bird feeding damage and any other disorders (Fig. 1). Dry ears were shelled and coarse ground and mixed for sub-sampling consistency. Sub samples were collected and finely ground for DON analysis by quantitative ELISA analysis at the University of Guelph Ridgetown Campus mycotoxin lab.         

Figure 1. Some common corn ear moulds which can be observed in Ontario.


Results for the 2023 survey are presented in Table 1. While there were many clean samples, more samples than normal displayed some background level of ear mould. DON concentrations were higher than long term survey averages (Table 2).  There also appeared to be a slightly greater incidence of insect feeding damage in the 2023 survey. As is usual in a year conducive for ear mould establishment and growth, these samples were associated with  greater visual ear moulds. Many mouldy samples had no ear damage however, suggesting weather and hybrid susceptibility were still primary factors for fungal infection. 

Table 1. Deoxynivalenol (DON) results from the 2023 Ontario grain corn ear mould and DON survey.

DON Concentration parts per million (ppm)All Samples*
Total Samples192
< 0.50 ppm41%
0.50 to <2.00 ppm36%
2.00 to <5.00 ppm18%
5.00 ppm and greater5%
* percentages may not sum to 100 due to rounding

Table 2. DON results from the past ten Ontario grain corn ear mould and DON surveys.

DON Concentration (ppm)2013201420152016201720182019202020212022
< 0.5083%66%75%48%69%33%84%58%63%88%
0.50 to <2.0015%26%20%26%17%27%12%31%26%10%
2.00 to <5.001%6%5%18%8%15%4%10%10%2%
5.00 and greater0%2%0%8%6%25%0%0%1%1%

Distribution of samples and their corresponding DON levels are presented in Figure 2. Even with 77% of 2023 samples testing below 2 ppm, growers should be vigilant, as they may have fields with elevated DON. Fields should be evaluated for risk and consider harvesting and drying higher risk fields before infections worsen. Understand management and storage options for corn with higher DON concentrations (see “Going Forward” below). Ear moulds and mycotoxins occur every year in Ontario and fields need to be assessed individually.  

Figure 2. Corn ear mould and deoxynivalenol (DON) survey sampling locations and results in 2023.

Growing Season

Planting was slightly delayed as lingering rains and cooler weather limited soil drying through early May. Once conditions were fit, planting progressed rapidly (~ 2nd and 3rd week of May for many areas). Weather generally remained sunny and dry through planting. Except for the odd rain event, sunny, hot and dry conditions dominated through to later June.  Starting the last week of June, general instability took over and rainfall events started across many areas. Frequent rainfall events and thunderstorms continued through July.

Some of the earliest fields started tasseling the third week of July, though the last week of July and first week of August appeared to be the peak for pollination across large parts of the province. Frequent rainfall continued through August and into early September for many areas. Corn canopies remained wet for long periods even when it wasn’t raining. Wet conditions at silking are very favourable for ear mould establishment while wet conditions through grain fill allow continued development. With lower-than-normal heat unit accumulation in 2023, the corn crop is less mature and higher moisture than normal in many cases. This can be a risk for continued ear mould activity until grain moistures or temperatures drop enough to limit activity.

Feeding Damage

Ear feeding by pests, particularly western bean cutworm (WBC), corn earworm (CEW) or birds can open husks and damage kernels which present opportunities for greater ear mould infection and DON. While still only representing a minority of samples, feeding damage appeared more common than what has been observed in recent surveys. Peak WBC moth flights generally occurred towards the very end of July through the first full week of August, generally coinciding with the latter half of tasseling in many areas. Where feeding damage was present, visual mould symptoms were usually more apparent.  

How to Sample Corn Loads

The importance of collecting representative samples cannot be emphasized enough. Significant variability in mycotoxin testing results can come from poor sampling.

Collecting a Bulk Sample from a Corn Load

While sampling from the top of a storage bin, truck or combine may be convenient, mycotoxins are rarely distributed evenly in grain loads, hence a sample probe is recommended. The more probes the better, but Ontario research shows that 4 probes sampling the full depth of wagons or trucks can do as good of a job representing corn loads as frequent tailgate sampling (swiping stream). Probes are not the major driver of variability experienced with DON testing. For moving grain streams, use a diverter or randomly collect cups of grain. Mix all collected probes/samples into one bulk sample of at least 2 kg.  

Collecting an Analysis Subsample from a Bulk Sample

Ontario research shows that one of the most significant sources of variability in DON testing comes from collecting the subsample for DON analysis (e.g. the amount of the 2kg bulk sample that is finely ground for the DON test). Because individual kernels can be highly variable in DON and still coarse in size relative to the analysis subsample (e.g. a 200g whole kernel sample used for fine-grinding may be representing the entire load with only 500 kernels), the whole bulk sample should be ground (at least coarsely) and mixed so the analysis subsample contains parts of all kernels in the bulk sample. This subsample can then be ground finer to meet specifications of the DON test. More details on reducing sample variability through proper sampling and grinding is available HERE. Remember, samples must be processed quickly – ship or deliver fresh sample promptly. The longer the sample sits around the greater potential for inaccurate results.

Going Forward

This survey does not capture all regions of the province and results can vary from field to field depending on local weather, hybrid, planting date, insect feeding, rotation, residue levels, fungicide practices and moisture. Results may not capture what is occurring in your field, therefore monitoring is always recommended. Timely harvest is important. Leaving infected grain in the field allows ear rot fungi to continue growing, which increases risks of mouldy grain and mycotoxin contamination. Most ear rot fungi continue to grow (and potentially produce mycotoxins) until grain moisture is below 15%.  In high risk or severely infected fields, growers should consider harvesting at higher moisture and drying below 15%. 

If a field contains significant ear moulds (e.g. 10% or more ears with visual mould symptoms) collect a representative sample prior to harvest and test for mycotoxins before storing or feeding to livestock. A lab test is the only reliable way of determining mycotoxin levels. 

If possible, segregate contaminated corn separately. 

When ear rots are present, the following harvest, storage and feeding precautions are advisable (adapted from OMAFRA Pub 811, Agronomy Guide for Field Crops):

• Harvest and dry as quickly as possible, especially susceptible hybrids. Mould and mycotoxin development ceases with grain moistures below 15%.

• If insect or bird damage is confined to certain areas, harvest and handle damaged rows separately.

• Cob, small kernels and fines typically have higher DON concentrations. Adjust harvest equipment to minimize grain damage and to remove insect damaged, infected or smaller tip kernels. Removing these parts when possible can be beneficial, though large amounts of removal may be required to significantly change grain concentrations.

• Clean bins before storing new grain and cool grain after drying. If possible, segregate corn by DON content to help match end use.

• Check stored grain often for temperature, wet spots, insects and mould. For grain with elevated mould content, market as soon as possible. Avoid long term storage.

• Exercise caution handling or feeding mouldy corn to livestock, especially hog breeding herds and weanling pigs. Pink or reddish moulds are particularly harmful. Test suspect samples for toxins. Work with a nutritionist to manage DON levels in feed.

Preventing ear rots and mould can be difficult since weather is critical to development. A few things to consider for 2024. Hybrid selection is important, and while tolerant hybrids are available, none have complete resistance. Growers are encouraged to discuss ear mould tolerance with their seed supplier. The Ontario Corn Committee has initiated inoculated DON trials for evaluating differences in DON susceptibility across Ontario hybrids. Crop rotation may help reduce ear rots, while certain foliar fungicides are also registered for suppressing ear rots but need to be applied at VT/R1 when silks are green. Cultural practices such as tillage are shown to have limited success in preventing ear and kernel rots.

Agricorp customers with mould issues are encouraged to immediately contact Agricorp at 1-888-247-4999 and report damage.

Additional Resources

For additional information, see the Crop Protection Network’s “Corn Management Disease Series – Ear Rots” publications at CropProtectionNetwork.org

CPN-2001 – Corn – An Overview of Ear-Rots

CPN-2002 – Corn – Mycotoxin FAQs

CPN-2003 – Corn – Grain Sampling and Mycotoxin Testing

CPN-2004 – Corn – Storing Mycotoxin-Affected Grain

Additional articles on managing corn ear moulds and mycotoxins are also available at FieldCropNews.com.

DON in Corn Silage

Harvest Tips for Mouldy Corn

Laboratories Offering Mycotoxin Analysis in Ontario

Good Mycotoxin Test Begins with a “Representative” Sample

Reducing DON Variability in Testing Truckloads of Corn – Prototype Grinder

End Uses for Mouldy Corn

To Clean or Not to Clean? Managing DON in Grain Corn

Fall Storage Tips for Mouldy Corn

Destroying a Corn Crop at Harvest Time

Land Application of Crops and By-products with Elevated DON Levels

Spring Storage Tips for Mouldy Corn


Sincere thanks to those who assisted in co-ordination and collection of samples: Agris Co-operative, Alliance Agri-Turf, Anderson Agronomy Services, Belmont Farm Supply, Benjamins Agronomy Services,  Clark Agri Service, FS Partners, Harriston Agromart, Hoegy’s Farm Supply, Holmes Agro, MacEwen Agricentre Inc., Midwest Co-op, Millstone Crop Services, Oxford Agropro Ltd., Parrish and Heimbecker, P.T. Sullivan Agro Inc., Sylvite Agri-Services Ltd., TCO Agromart, The Andersons Canada Ltd., Trouw Nutrition, Wellburn Agromart and the many producers and OMAFRA staff also involved. This co-operation is critical for covering as much of the corn growing areas of the province as possible in a short period of time.

Thanks to Grain Farmers of Ontario, University of Guelph Ridgetown Campus mycotoxin lab and OMAFRA plant health fund for support of the survey as well as Ontario Agri-Business Association (OABA) and its members for their interest and participation.

This project was funded in part by the Sustainable Canadian Agricultural Partnership, a five-year federal-provincial-territorial initiative. 

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