Planting
In March 2024, Statistics Canada estimated Ontario farmers intended to plant 2.3 million acres of grain corn, 5% higher than the 5-year (2019-2023) average seeded acres of 2.2 million acres (OMAFA Crop Statistics).
Unsettled weather and highly variable planting progress dominated the spring of 2024. Frequent rains through April limited early corn planting. Frequent and spotty rains continued through most of May. During late April and the first week of May, planting was generally limited to well drained soils in areas not receiving rain. Planting continued where possible. By the end of the second full week of May (May 18), planting progress was still highly variable with some areas nearing completion while others had barely started; some estimated around half of the Ontario corn crop may have been planted by this date. Planting slowly wrapped up over the last two weeks of May, with exception of some heavier textured soils where planting continued into June. On heavier textured soils where rainfall was frequent (e.g. parts of Lambton, Middlesex, Bruce counties) not all intended corn acres were planted. Some fields intended for corn were switched to soybeans.
Early planted corn started to emerge the week of May 20. Growth was rapid with the warm temperatures, and corn planted in early May was around the V2-V3 stage (2-3 leaf collars) by the end of May.
Final Ontario grain corn planting estimates were 2.2 million acres (OMAFA Crop Statistics), slightly lower than the March planting intentions but similar to the 5-year average.
Early Season
Unsettled weather continued through June. Field activity occurred around rainfall as required. While temperatures and heat units were generally greater than normal, there were also several short periods of very cool weather. Side-dressing generally started by the first week of June. Many fields were closing rows by the week of June 23. By late June, crop heat units (CHU) were 100 CHU or more, which is approximately10% above the 10-year average for many parts of Ontario.
Pollination and Grain Fill
While sunshine generally dominated the first week of July, unsettled weather continued through the remainder of the month, including several very heavy rainfall events that affected wide parts of the corn growing regions of the province. With the exception of areas that suffered from extreme rainfall, corn generally looked good (height, colour, uniformity).
Some of the earliest planted fields (late April) were tasseling the week of July 14, while the week of July 21 was likely the peak for tasseling and pollination for much of the province’s corn crop. Later planted fields continued to tassel and pollinate after.
Western Bean Cutworm peak moth flights generally occurred the last two weeks of July, coinciding with tasseling and pollination in many areas.
Consistently wet corn canopies raised concerns around tar spot and ear moulds. Initial reports of tar spot started around tasseling, including areas outside of the traditional hotspot areas of southwestern Ontario.
Unsettled weather continued until the middle of August, then sunshine and warmer than normal temperatures took over through to late September. This likely marked the driest period of the growing season for most areas of Ontario.
By mid-September, many areas of Ontario were 50 to 100 CHU (approximately 1% to 4%) ahead of the 10-year average.
Corn Silage Harvest
Corn silage harvest started in many areas by the second week of September and appeared to be in full swing the following week. Except where corn was late planted, most corn silage harvest appeared to be nearing completion by the end of September. Like in 2023, 2024 silage harvest coincided with a stretch of well above normal temperatures (high 20’s to low 30 degrees Celsius). Fast dry down may have hastened harvest and required careful management for silage harvest moistures. An estimated 231,000 acres of corn silage was harvested (OMAFA Crop Statistics), slightly lower than the 5-year average of 249,000 acres. Average yields were 17.6 ton/ac, 88% of the 10-year (2014-2023) average of 20 ton/ac (OMAFA Crop Statistics).
Ear Moulds and DON
Where Western Bean Cutworm, Corn Earworm feeding damage was present, visual mould symptoms were usually more apparent. While only representing a minority of samples, insect feeding damage appeared slightly more common in some areas than had been observed in recent surveys. Peak Western Bean Cutworm moth flights occurred the last two weeks in July, generally coinciding with tasseling in many areas.
The annual ear mould and DON (vomitoxin) survey occurred between September 23 and October 3. The purpose of the survey is to estimate the relative levels of DON in the grain corn crop just prior to harvest to provide information for growers and industry. A total of 261 samples were collected across the province. Visual mould and DON levels were lower than normal with 6% of samples testing at or above 2 ppm (10-year average is 14% of samples at or below 2 ppm). The final report is available at Fieldcropnews.com (https://bit.ly/4fZHGlr ).
Grain corn DON levels were generally very low across most of the province at harvest. Given the frequent rainfall and wet corn canopies, there had been concerns that DON could have been a significant issue in 2024, so this was positive. Factors which likely contributed to reduced ear rot and DON levels this year include: i) unlike past elevated years (2016, 2018, 2023), 2024 did not start with an extended dry period from planting through to pre-tassel, which can influence spore release timing and plant stress, ii) warmer than normal temperatures may have limited ear mould establishment and growth and iii) from August through September conditions were generally dry which may have limited growth of any established ear moulds.
Corn hybrid selection has one of the most significant impacts on DON levels in grain corn (second only to weather). Talk to your seed supplier about ear rot and DON hybrid ratings. Further information around hybrid risk is now available through the Ontario DON hybrid trials. Results were released for the first time in February 2024 and are available in the corn section of gocrops.ca (https://bit.ly/4itaqoh ). The 2024 report is expected to be released in January 2025.
Tar Spot
Tar spot was likely the biggest corn story of 2024. Weather in 2024 was conducive for tar spot development (moderate temperatures, prolonged leaf wetness) and heavy pressure in the traditional tar-spot hotspots (e.g. south and west of London and north shore of Lake Erie). First observed in 2020, 2024 was the first year where fields outside of the traditional hotspots reached significant yield loss levels, including fields in counties such as Huron, Perth, Oxford and Brant. It was also the first year observed east of Toronto and into Quebec, however infection was late and levels were generally low in these regions, but the disease is likely to overwinter and establish. Follow maps of tar spot development in real time across North America at Crop Protection Network .and download the Tarspotter app to help determine your risk in 2025. Tolerant hybrids and tar spot fungicides (VT/R1) can help limit yield losses in years that are conducive for high tar spot pressure.
Grain Corn Harvest
Extra heat in September and a later than normal frost was very welcome to move grain fill along in parts of the province where corn was planted very late. Some light frosts (e.g. light frost on roofs) occurred the week of October 6 while the first real killing frost (e.g. -2°C or less) for many corn growing areas did not occur until two weeks later, around October 18.
Above average heat unit accumulation and a dry fall led to an early and quick harvest in many areas. While some grain corn harvest started as early as the end of September, harvest appeared to start in earnest around the Thanksgiving weekend (October 14). By the first week of November, many areas appeared to have most of the corn harvested. Well above normal temperatures and minimal rainfall provided great harvest conditions.
In general, many reported average to above average (or record) yields. Some reported yields were trimmed in areas of heavier or poorly drained soils where excessive rainfall events were received, though these were relatively localized.
Estimated 2024 grain corn yield for Ontario is 180 bu/ac (OMAFA Crop Statistics), 8% higher than the 10-year average of 166 bu/ac (2014-2023). The 2024 Ontario hybrid corn performance trials results are available in the corn section of https://gocrops.ca/
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 2025 and Beyond
Tar Spot
Ontario corn growers should remain vigilant and be aware of how to identify and manage tar spot. Tar spot will be an issue in 2025 but to what degree depends on location, weather conditions and on the tar spot fungus biology, infection timing (early/late season), spore levels (high/low) and dispersal of spores locally, regionally, and from the US Midwest.
Tar spot is spread by wind-blown spores and can be identified on the leaf by black “tar-spot” fruiting structures (stromata) on corn leaves and husks (Figure 1).
Cool and humid canopies with prolonged leaf wetness like 2024 are favourable for tar spot development. Infections are most severe in corn-on-corn fields where tar spot was present in the past. Corn residue serves as a source of inoculum for earlier and more severe infections. In environments with high pressure, tolerant hybrids and fungicides with high efficacy against tar spot have the ability to limit yield losses. Ontario research is looking at hybrid tolerances and fungicide management options. For more information, see resources at FieldCropNews.com or CropProtectionNetwork.org.
Figure 1. Black tar spot stromata on corn leaves in an Oxford County field in September 2024.