Testing has revealed higher levels of deoxynivalenol (DON) in Ontario's 2026 corn crop compared to recent years, although contamination remains well below the extreme levels recorded in 2018.
The annual Ontario corn ear mould and DON mycotoxin survey found that 77% of samples tested below 2 parts per million (ppm), compared to the 10-year average of 86%. Results were similar to those recorded in 2016 and 2023.
The survey was conducted by field crop specialists with the Ontario Ministry of Agriculture, in collaboration with Grain Farmers of Ontario (GFO) and members of the Ontario Agri-Business Association (OABA).
Between Sept. 23 and Oct. 9, a total of 272 corn ear samples were collected from fields across the province.
The results showed that 54% of samples contained DON concentrations below 0.5 ppm, down from 88% in 2025. Another 23% tested between 0.5 and 2 ppm, compared to 10% last year.
Meanwhile, 17% of samples contained DON concentrations between 2 and 5 ppm, up from just 2% in 2025. Another 6% tested at 5 ppm or higher, compared to none last year.
Despite the increase, contamination was considerably less severe than in 2018, when 25% of samples tested at 5 ppm or higher and only 60% were below 2 ppm. In that year, GFO estimated industry and producer losses at roughly $200 million.
DON, also known as vomitoxin, is produced primarily by Gibberella and Fusarium ear moulds. It can cause significant price discounts for producers, and problems when contaminated grain is fed to livestock, particularly hogs.
Although some samples displayed visible ear mould symptoms, many showed little or no evidence of mould, highlighting the importance of testing rather than relying solely on visual assessments. The survey also emphasized that DON concentrations can vary considerably between individual fields.
Factors influencing contamination include hybrid susceptibility, planting dates, pollination timing, rainfall patterns, insect feeding and crop stress. Foliar diseases such as northern corn leaf blight and tar spot can also contribute indirectly by increasing plant stress.
Growers are encouraged to remain vigilant, assess individual fields for contamination risks and prioritize higher-risk fields for harvesting and drying.
The ministry noted that prompt harvesting and drying can help prevent additional mould growth and DON accumulation, particularly where weather conditions favour further disease development.
