Field Observations

June 25, 2026

Timely rains have allowed grain crops across the province to flourish as the month comes to a close. With corn, soybeans, and spring cereals growing vegetatively, and winter wheat in the grain-fill stages, it is still important to actively scout fields for insects, disease, and weeds.

Corn

Rain and moderate temperatures over the past week have helped corn progress quickly. There is still a high degree of variability in crop staging across the province, from V1 to V9.

At about the V6 stage (six collars, or eight-leaf stage), the growing point emerges above ground level. The critical stage of ear development runs from this stage to about a week before pollination. Ear initiation begins, and kernel rows per ear are then determined. The number of kernels per row is determined as the ear elongates, before pollination. Stress in the coming weeks from a lack of nutrients or moisture will reduce grain potential through reduced kernel numbers. Stress can be caused by many factors, including populations that are too high, weed pressure, root pruning from machines or insects, lack of fertility, lack of rainfall, standing water, hail damage, and disease.

Rapid growth syndrome has been seen, and can continue to appear in fields experiencing shifts from cool conditions to high heat. The syndrome occurs when corn leaves do not unfurl properly, and the whorl becomes tightly wrapped and twisted.

Be aware of crop stage as resprays occur and consider that some plants may be more advanced than much of the field, which could increase the risk of herbicide injury.

Side-dressing and top-dressing are occurring. With recent heavy rains, there have been questions about nitrogen losses. Several factors can affect losses, and there is no firm answer on total loss potential.

• The greatest chance of nitrogen loss is in areas where water has been sitting in fields. The longer water has sat in a field, creating saturated conditions, the higher the chance of loss through denitrification.
• Cooler temperatures also come into play. Typically, there is less loss under cool conditions.
• If all nitrogen was applied pre-plant, losses will likely be higher than if some was side-dressed in the past couple of weeks. Overall, the consensus is that urea and UAN take one to three weeks to convert to nitrate, so the longer they have been applied, the higher the chance of loss.
• PSNT testing can help determine the level of nitrogen in the soil.

As fungicide timing approaches, be aware of the potential for tar spot and Gibberella ear rot, which can cause DON in corn. Scout fields for disease, as the plant is vulnerable to tar spot between V10 and R3 (milk stage). The Ontario Corn Committee shared the 2025 Ontario Corn Hybrid DON Screening Trials last fall. These trials may be helpful in determining how susceptible hybrids are to Gibberella ear rot and DON accumulation. Use them as a tool as fungicide spraying approaches. Tar spot has been identified in Indiana so far this year.

Soybeans

Soybean fields are staging from VE (emergence) up to beginning bloom (R1, when plants have at least one flower at any node). Soybean planting has mostly wrapped up in areas that struggled to plant earlier this year, and some replants are also occurring. Heavy rains last week caused ponding in some fields.

In the V3 to V5 stages, axillary buds develop into flower clusters near the top of the stem. In the coming days, flowering will begin, starting on the third to sixth nodes and continuing down the stem. At this point, the plant will transition into reproductive stages (R1) while continuing to grow vegetatively.

As resprays occur, be sure to mitigate drift. Both BeDriftAware.ca and a past Grain Farmers of Ontario GrainTalk webinar with Dr. Jason Deveau have valuable tips for spraying to help mitigate drift.

Agricorp planting deadlines and reporting of final acres for soybeans are due June 30.

Cereals

Spring cereals are in the stem elongation to boot stage.

Winter wheat harvest will begin gearing up in the next couple of weeks in the deep southwest. As harvest approaches, scout for fusarium-damaged heads in the field. Infected fields should be harvested first to limit continued toxin buildup in case of rain events or delayed harvest. Set the combine correctly to help blow out the lighter infected kernels. Fusarium can show up even at very low levels after a T3 application, sometimes only infecting a few florets on a few plants within a field. This might be due to T3 fungicides being applied at the ideal timing for most of the field, while some tillers may have pollinated at a slightly different time. The incidence of fusarium infections has been reduced over the past 20 years due to genetic improvements and the use of fungicides during pollination (T3 timing) to help control fusarium. This spring, some regions of the province saw ideal conditions for fusarium development, while others did not. Think of the disease triangle for fusarium infection: susceptible host, pathogen, and favourable environment. Farmer practices have helped reduce the chance of infection.

Across much of the province, kernel fill is still occurring in the winter wheat crop (GS 73 early milk to GS 83 early dough). Over the past few weeks, grain-fill weather has been nearly ideal, with moderate temperatures and timely rains. Prolonged hot, dry weather would limit kernel fill, resulting in smaller kernels as water availability for the crop becomes limited, and the plant progresses rapidly through growth stages. Kernel abortion and dead heads could also be seen as the plant dies rather than matures if moisture becomes too limited during this period, often seen on sandy knolls within fields in past years.

Heavy rains affected parts of the province over the past week, causing lodged wheat in some cases. These fields should be prioritized for harvest, as lodged wheat can often create ideal conditions for disease.

Cereal leaf beetles, cereal aphids, and true armyworm have all been identified in Ontario fields, with some populations meeting thresholds. Scout for these pests, monitor, and control as needed. Keep pre-harvest intervals in mind, as wheat harvest is quickly approaching for some. More information on these pests can be found in past Field Observations.