Co-authored with Albert Tenuta, Field Crop Pathologist, OMAFRA.
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 2022 survey found 98% of samples tested low (<2.00 parts per million (ppm)) for DON, suggesting levels are lower than long term survey averages but local conditions should be considered when evaluating field risk.
Methods
From September 28 to October 5, 2022, 193 ear corn samples were collected from across the province. Five consecutive ears were collected from four random locations throughout a field and placed into high temperature driers (80°C) as soon as possible after collection. Pictures were taken to document moulds and insect/bird feeding damage (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. Corn ear moulds which can be observed in Ontario.
Results
Results for the 2022 survey are presented in Table 1. Visual mould and DON concentrations were lower than long term survey averages (Table 2). While ear moulds were evident in some samples, severity was usually very low. Many displayed no symptoms, and only one sample tested 5 ppm or greater. Like recent years, insect feeding appeared very low, but where present was often associated with visual ear mould. Other mouldy samples with no ear damage were observed where weather and hybrid susceptibility were likely factors.
Table 1. Deoxynivalenol (DON) results from the 2022 Ontario grain corn ear mould and DON survey.
| DON Concentration Parts per Million (ppm) | Samples* |
| Total Samples | 193 |
| < 0.50 ppm | 88% |
| 0.50 to <2.00 ppm | 10% |
| 2.00 to <5.00 ppm | 2% |
| 5.00 ppm and greater | 1% |
Table 2. DON results from the past ten Ontario grain corn ear mould and DON surveys.
| DON Concentration (ppm) | 2012 | 2013 | 2014 | 2015 | 2016 | 2017 | 2018 | 2019 | 2020 | 2021 |
| < 0.50 | 84% | 83% | 66% | 75% | 48% | 69% | 33% | 84% | 58% | 63% |
| 0.50 to <2.00 | 12% | 15% | 26% | 20% | 26% | 17% | 27% | 12% | 31% | 26% |
| 2.00 to <5.00 | 4% | 1% | 6% | 5% | 18% | 8% | 15% | 4% | 10% | 10% |
| 5.00 and greater | 0% | 0% | 2% | 0% | 8% | 6% | 25% | 0% | 0% | 1% |
While 98% of 2022 samples tested below 2 ppm, growers should still remain vigilant and understand management options in fields with higher DON concentrations. Ear moulds and mycotoxins occur every year in Ontario and fields need to be assessed individually. Distribution of samples and their corresponding DON levels are presented in Figure 2.
Figure 2. Corn ear mould and deoxynivalenol (DON) survey sampling locations and results in 2022.
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 to 3rd week of May for many areas). Weather generally remained sunny and dry through planting. Except for some scattered showers and local pockets that received heavier rains, the southwest remained predominantly dry through June and July. Widespread rain events were more common in central and eastern Ontario where moisture stress was generally less of a concern.
Tasseling started as early as mid-July, though the last week of July was generally the peak for pollination across large parts of the province. Dry conditions (and moisture stress in very dry areas) generally dominated through most of tasseling. This likely delayed ear mould inoculum production and limited establishment during the early fresh silk window. By early August, widespread rain events covering much of the province became more common and remained relatively steady for many areas through September. Where ear moulds had established, these conditions were likely favourable for continued growth/development.
Feeding Damage
Ear feeding by pests, particularly western bean cutworm (WBC), corn earworm (CEW) or birds can open husks, damage kernels and present opportunities for greater ear mould infection and DON. Feeding damage appeared very low in 2022 survey samples. Peak WBC moth flights generally occurred late July to early August, slightly after tasseling. Where feeding damage was present, visual mould symptoms were often more apparent.
How to Sample Corn Loads
The importance of collecting representative samples cannot be emphasized enough. Significant variability in mycotoxin testing 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 as frequent tailgate swiping for representing corn in those loads and is not a major driver of variability 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. At least 2 kg of corn should be collected from each load.
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 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 subsample 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.
Last, 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 diseased 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 (10% or more ears with 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.
• Adjust harvest equipment to minimize grain damage and to remove insect damaged, infected or smaller tip kernels. Clean corn thoroughly to remove cob, small kernels and red dog which may be infected.
• 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 2023. 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. After environmental issues in 2019, protocols have been refined over the past couple growing seasons. 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
Crop Protection Network Publications:
CPN-2002 – Corn – Mycotoxin FAQs
CPN-2003 – Corn – Grain Sampling and Mycotoxin Testing
CPN-2004 – Corn – Storing Mycotoxin-Affected Grain
Acknowledgements
Sincere thanks to those who assist in co-ordination and collection of samples: Agris Co-operative, Alliance Agri-Turf, Anderson Agronomy Services, Belmont Farm Supply, Campbellford Farm Supply, Clark Agri Service, FS Partners, Harriston Agromart, Hoegy’s Farm Supply, Holmes Agro, MacEwen Agricentre, Maizex Seeds, Midwest Co-op, Millstone Crop Services, Oxford Agropro, Parrish and Heimbecker, P.T. Sullivan Agro, St. Lawrence Grain & Farm Supply, Sylvite, TCO Agromart, The Andersons, Wellburn Agromart, Yantzi Feed and Seed 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 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 Canadian Agricultural Partnership, a five-year federal-provincial-territorial initiative.
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