Ontario corn DON levels slightly exceed the 10-year benchmark

By Olivia Hart

Seventy-seven per cent of 272 Ontario grain corn ear samples had DON levels below 2 parts per million (ppm) in 2026. That share sat nine percentage points below Ontario's 10-year average of 86 per cent, confirming that contamination was slightly higher than normal across the province.

In practical terms, nine more samples per 100 fell outside the under-2-ppm group than the 10-year benchmark.

Most corn fields recorded low contamination, but the reduced share in the lowest reported category means growers should not treat the provincial result as a guarantee for every field. DON, also called vomitoxin, remains the contaminant measured by the annual survey.

The 2026 result closely matches the 2016 and 2023 surveys and remains significantly lower than the record-high levels of the 2018 outbreak. Most grain remains in the lower-risk categories identified in the report, although variable conditions created distinct windows for DON accumulation.

Ben Rosser, Ontario corn specialist, and Albert Tenuta, field crop pathologist at the Ontario Ministry of Agriculture, Food and Agribusiness, co-authored the annual survey. Grain Farmers of Ontario and the Ontario Agri-Business Association collaborated on the project. It evaluated 272 ear corn samples collected across Ontario between Sept. 23 and Oct. 9, 2026.

The University of Guelph's Ridgetown Campus Mycotoxin Lab tested the samples using quantitative enzyme-linked immunoassay, or ELISA. The 77 per cent finding measures the proportion of samples below 2 ppm rather than the average concentration across all grain. It shows how many samples occupied the survey's lower-risk grouping.

Ben Rosser and Albert Tenuta wrote in the survey findings: “Variable growing conditions across Ontario created localized windows for ear mould development and DON accumulation.”

What drove mycotoxin risk?

The authors divide the risk drivers into three stages of the crop cycle.

• Planting delays: Frequent May rains delayed planting into late May or early June on heavier clay soils.
• Pollination and wet canopies: Uneven summer rainfall stretched pollination from mid-July into August. Frequent August showers, cool night temperatures and heavy morning dews kept canopies wet for long periods, encouraging Gibberella infection.
• Late-season crop stress: Northern corn leaf blight, tar spot and insect feeding from western bean cutworm created kernel entry points and added plant stress during grain fill.

The survey links three pressures rather than one uniform provincial condition. A late-planted field on heavier clay faced a different set of conditions from an earlier field, while wet August weather and crop stress shaped infection and insect damage. Provincial data establish the scale; local conditions determine which fields warrant closer attention.

What should growers do with the results?

The full report by Rosser and Tenuta on Field Crop News contains complete regional sampling maps, 10-year comparative trend tables and video guides on proper sampling protocols. It also carries hybrid selection recommendations for 2027. Those resources matter because a provincial percentage cannot identify the conditions around an individual field.

For growers, those materials turn a provincial result into a local decision tool. Regional maps and trend tables place sampling history and seasonal results in context. Sampling videos establish a consistent collection method, while hybrid recommendations address the next planting cycle.

The practical sequence is to check local conditions, follow the sampling protocol before drawing conclusions, and use the 2027 advice when selecting seed. That sequence preserves the link between the measured result and the weather and crop stresses that produced it.

The 2026 data are available now through Field Crop News. The next explicit decision point is the 2027 hybrid cycle, when growers should review the report's recommendations against the late-planting, wet-canopy and disease pressure risks that shaped this season.