Crop Report – May 18th, 2022

Figure 2. Corn coleoptile ready to emerge from a sandy loam in Eastern Ontario on May 13th.


Large swaths of the province saw rain early this week, which put a pause on a very productive planting window over the previous week and a bit. The forecast predicts slower progress due to more regular precipitation, which will provide some stress relief on fields that were starting to turn alarmingly dry.

Figure 1. Difference from normal precipitation April 17 to May 17th.
Figure 1. Difference from normal precipitation since April 15th.

Northwestern Ontario is experiencing many of the same issues with flooding and continued cold and wet conditions as we’ve heard from Manitoba and are struggling to maintain their normal field schedules.


Winter wheat continues to march along well, with flag leaves detectable in early-planted fields in the Southwest. Some powdery mildew has been reported in the Southwest. Management decisions should be based on the severity of disease on the 2 leaves immediately below the flag leaf. If the disease slows down with warm, dry weather and doesn’t move up the canopy, intervention can wait. If growing a susceptible variety and the disease is getting close to the flag leaf, growers should consider a fungicide application before T3. Powdery mildew symptoms on the flag leaf (1% of the leaf) and the second leaf (3%–5% of the leaf) require immediate attention, especially if prolonged wet, humid weather is forecast.

Many spring cereals are still in the critical weed-free period (up to third leaf, GS13). Recent rains will likely induce a flush of annual weeds which will need to be controlled.


With the heat and now rain, forages will grow and advance through maturity stages very quickly. Between wetter weather, ideal maturity for first cut, and the pressure to plant, it can be difficult to prioritize the spring workload. Those aiming for high-quality hay should park the planter and harvest forage at ideal maturity. This 20-minute presentation from MSU Extension forage specialist Kim Cassida breaks down the relative cost of losing digestible fibre in the forage versus incremental yield loss from delayed corn planting.

Corn and Soybeans

With the excellent planting conditions of the past 10-14 days, the majority of the corn and an estimated 15% of soybean acres have been planted. With local variability, 70-80% of acres were planted by the time rain chased planters out of fields. The unseasonably warm weather has meant rapid CHU accumulation to the point that much of the recently planted corn has germinated and some is even starting to emerge (Figure 2).

Figure 2. Corn coleoptile ready to emerge from a sandy loam in Eastern Ontario on May 13th.

Water-collecting low areas of landscapes and areas of high clay were less uniformly fit, and planting continues to lag behind. Outside of the Southwest, corn yield potential will start to decline quickly with delayed planting by the end of this week based on historical Ontario data. As difficult as it can be, it’s important to weigh the relative impacts of later planting compared to planting into unfit soils. Working soils too wet will result in cloddy seedbeds that can increase soil moisture and seed-soil contact variability, reducing stand uniformity and impacting yields. Shallow or seed-trench compaction might not be visible until later in the season, at which point it will be too late to do anything about root-limiting layers that will increase the crop’s vulnerability to weather conditions.

Areas of the province that got heavy rains over the past few days may be at risk of crusting.


Spring canola planting progress has been good across Northeastern Ontario and some canola has emerged. Temperatures will be low in the region over the next week but at this time there is no frost in the forecast. Flea beetle likely emerged from overwintering sites during warmer temperatures last week. Although they appear to be less active during cool temperatures, they continue to feed and may cause more damage by feeding on stems while hiding underneath plants.

Winter canola has advanced rapidly in the past week and is either approaching or beyond 50% bloom. Fungicide applications to prevent white mould should be applied at 20 – 50% bloom, which is when approximately 15 to 25 flowers are open on the main stem. Applications beyond 50% bloom have low return on investment. Monitor for cabbage seedpod weevil and scout using a sweep net. Note that if the threshold of 2-4 weevil per sweep is met, control with an insecticide is ideally timed when pods are first formed and are less than an inch in length. This may coincide with the later part of the fungicide application window.

Weed Control

Rain will have activated residual herbicides in most fields. These need to be drawn into solution (i.e. into soil water) in the rooting zone of germinating weeds to be effective. Scouting at 7, 14, and 21 days after residual herbicide application to evaluate weed pressure and weed stage is important for best application timing of post treatments.


Known Alfalfa Snout Beetle infestations in eastern Ontario include fields on Wolfe Island, in the Prescott/Brockville area, in Kemptville and at the Central Experimental Farm at Agriculture and Agri-Food Canada. New detections of Alfalfa Snout Beetle near Merrickville and Finch were reported this week. Report any adults found outside of the known areas to Tracey Baute, OMAFRA Entomologist Field Crop at There are no thresholds and chemical control options are not effective. Biocontrol nematodes applied in the fall on newly infested fields have been successful at suppressing populations in New York. For new information on Alfalfa Snout Beetle sites (eastern and central Ontario), please visit this recent article on Field Crop News.  

Cereal leaf beetle (CLB) is showing up in some winter wheat fields, though numbers are currently low. CLB adults and larvae will move to emerging spring cereal fields and scouting is recommended. Recent observations are indicating that CLB are particularly fond of oats. The action threshold for control is warranted if an average of 3 larvae per tiller are found before boot stage. One CLB adult or larvae per stem warrants control after boot stage but prior to heading stage. If significant feeding is taking place on the flag leaf in the early heading stages, control may be warranted. Natural enemies are highly effective at controlling this pest. For the safety of these natural enemies, chemical control is not recommended unless pest population exceeds the action threshold.