In March 2021 Statistics Canada estimated Ontario farmers intended to plant 2.2 million acres of grain corn, 3% higher than the 5-year (2016-2020) average seeded acres of 2.14 million acres (OMAFRA Crop Statistics).

Spring 2021 provided a great start for planting. While April generally remained cool, lack of rainfall provided excellent soil conditions with many in Southwestern and Midwestern Ontario starting corn planting in earnest the last week of April. Some light rain and well below seasonal temperatures slowed planting progress the first week of May. A significant amount of corn was planted across the province the second week of May, with many areas wrapping up by the end of this week (May 15). Heavier or poorly drained soils were generally wrapping up by the end of the following week (May 22).

Given the cool start, corn planted early (April) took several weeks to emerge. Summer-like temperatures through the later half of May resulted in rapid corn emergence for corn planted after the May cold spell, and often not far behind the early planted corn. There were some concerns over weed control or herbicide options given how quick corn emergence was. Soil conditions remained fit however, and except for some fields planted just prior to the cold weather, stand emergence and uniformity looked excellent across most parts of the province.

Final grain corn planting estimates for the province were 2.15 million acres (OMAFRA Crop Statistics), slightly lower than March Statistics Canada planting intentions, and very similar to the 5-year planted average.

Early Season

OMAFRA completed its annual Pre-Sidedress Nitrate Test (PSNT) survey May 31 to June 2. The survey samples corn fields around V3-V4 stage, measuring background soil nitrogen supply in fields not receiving preplant nitrogen to gauge soil nitrate levels just prior to sidedress. Like 2020, sunshine and little rain produced great soil conditions in early spring. Cold temperatures dominated for 1-2 weeks in early May followed by seasonal to above seasonal temperatures into late May and early June. Given the temperature variability, there was interest in how nitrogen mineralization my have been influenced.

In 2021, the average PSNT survey value was 13 ppm, comparable to the long-term (2011-2020) average of 12 ppm. This suggests natural soil nitrate supply in 2021 may have been the same or slightly higher than normal. Each 5 ppm change in PSNT generally changes N recommendations by 25-30 lb-N/ac, while every 1 bu/ac change in yield expectation changes OMAFRA N recommendations (N-calculator and PSNT) around 0.80 lb-N/ac. Actual changes depend on soil nitrate level and yield goal (see PSNT recommendations at Optimum nitrogen rates in corn are a function of both nitrogen supply (soil mineralization) and demand (yield). While conditions remained on the drier side, yield potential was looking excellent by mid June.   

June was generally favourable for in-crop management such as Nitrogen sidedressing. Earlier sidedressing on early planted corn generally started later May into early June. Most timely planted fields were closing rows by mid June. Despite limited rainfall since planting, the corn crop looked excellent across most parts of Ontario. Frequent and often heavy rainfall started for many parts of the province from the last week of June through mid August. Some of the highest rainfall amounts were in areas southwest of London where some corn fields started showing signs of stress (Figure 1.) such as pale colouring and lower leaf firing, especially between tile drains.

Figure 1. Corn field southwest of London showing stress and variability from excessive rainfall from late June through August.

Pollination and Grain Fill

A large amount of corn began tasseling and undergoing pollination by mid-July, with most fields fully tasseled by the last week of July. Except for areas where excess rain resulted in crop stress, field uniformity continued to look excellent. Ample soil moisture from frequent rains and moderate temperatures bode well for pollination and early kernel set.  

Frequent rain continued through tasseling and into mid-August in many areas. From an ear mould perspective, there were concerns 2021 was setting up like the high-DON year of 2018 with frequent rain and humidity leading to wet, humid corn canopies through silking and early grain fill. Wet corn canopies at silking are conducive for ear moulds establishing, while continued moisture after favour further growth.

Western Bean Cutworm (WBC) moth flights were consistent with recent years where moth flights begin to ramp up in latter July and peak around the first week of August. By this time, most of the corn had tasseled. Most egg laying in corn is expected to occur pre-tassel, so early corn tasseling may have reduced WBC pressure in corn in 2020. 


Earlier corn silage harvest generally started the beginning of September and was in full swing by mid September in many areas. Strong yields were noted in many areas.

The annual Ontario ear mould and DON (vomitoxin) survey was completed September 21to October 2. The purpose of the survey is to measure the relative levels of DON in the grain corn crop just prior to harvest to provide information for growers and industry. A total of 205 samples were collected across the province. Visual mould and DON levels were in line with long term survey averages, with 89% of samples testing low DON pressure (less than 2.00 ppm) and remaining 11% of samples testing 2 – 5 ppm. Samples were generally well distributed across the province, with some more higher testing samples in southwestern Ontario. As in most years, even those with low risks, there was still reports of elevated fields, so monitoring is always suggested. Final report is available at (

Insect feeding damage appeared relatively low in 2021 survey samples, possibly a result of corn tasseling prior to peak Western Bean Cutworm (WBC) moth flights (period of July 29 to August 4 on average for Ontario in 2021). Where feeding damage was present, visual mould symptoms were usually more apparent.

Some high moisture or early harvest grain corn had started late September and early October. With advanced maturity and good dry down, an early harvest appeared likely. However, very heavy rains late September followed by frequent rains through October hampered progress. Harvest ground on through October and early November, with many areas finishing by mid November. Harvest continued into December for areas with heavier and poorly drained soils.    

Many growers reported very strong, and in many cases, record yields. There were exceptions to this however, especially areas where the corn crop was stressed and did not recover from excessive rainfall in June and July.  

Reports of DON were generally low, though pockets of higher testing corn were reported at harvest. Given concerns over frequent rainfall and canopy humidity/wetness during pollination, conditions favourable for ear mould establishment and reminiscent of the high-DON year of 2018, this was welcome news. Unlike 2018, rainfall generally subsided through August and most of September of 2021. It is thought this may have limited development of ear moulds that did establish.  

Estimated yield for Ontario is 175 bu/ac (OMAFRA Crop Statistics), 109% of the 10-year average grain corn yield of 161 bu/ac (2011-2020) (OMAFRA Crop Statistics).

Ontario Corn Committee (OCC) 2021 hybrid trial results are available at the homepage of or Several options exist for viewing data, including printable PDF, sortable spreadsheets (yield index, moisture, lodging, company or hybrid name etc.) and yield by moisture graphs demonstrating the trade-off between yield and harvest moisture of hybrids within each OCC table.

Things to Watch in 2022


Tarspot is a foliar fungus first observed in Indiana in 2015. Its spores are windblown, and it has spread outwards since. First observed in Ontario in 2020 near Ridgetown, it appeared to overwinter into 2021. By September 2021, black fruiting structures (stromata, Figure. 2) could be found in corn in all counties west of Toronto. Like all diseases, there is variability in susceptibility across hybrids, but no resistance currently exists. Whether tar spot becomes an issue in 2022 depends on weather conditions. Cool and humid canopies with prolonged leaf wetness like 2021 are favourable for development. In 2021, infections were more severe in corn-on-corn fields where tarspot was present in 2020. Corn residue serves as a source of inoculum for earlier infection in those fields. Ontario research is looking at hybrid tolerances and fungicide management options. For more information, see resources at

Figure 2. Black tar spot fungal structures (stromata) and leaf necrosis (yellowing/browning tissue death) starting in an Elgin County corn field in late August 2021.

Corn Rootworm

In recent years, corn rootworm larvae feeding in corn fields with corn rootworm Bt protection has raised concerns about potential for Bt resistance. Generally, this is in or near fields with very long corn-on-corn In recent years, corn rootworm larvae feeding in corn fields with corn rootworm Bt protection has raised concerns about potential for Bt resistance. Generally, this is in or near fields with very long corn-on-corn rotations and repeated use of corn rootworm Bt hybrids. Fields have been observed in Huron, Perth and Durham Counties. Growers with a history of long corn-on-corn rotations using corn rootworm Bt protection should monitor fields for excessive corn rootworm beetle populations or lodging or goosenecking plants with larvae feeding. For more information, search “corn rootworm” at