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News Seeding/Planting Agronomy
Warmer temperatures and rain will speed up crop (and weed) growth

May 21, 2020  By OMAFRA Field Crop Team

Temperatures over the past week have been significantly warmer than the week prior. Most of the province saw rain over the long weekend. In many areas this was welcome news, but much of southwestern Ontario received significant downpours and flooded fields were a common sight.


Most of the intended acreage was planted before the recent rains. The remaining unplanted acreage is primarily in regions with heavy clay soils or lighter soils, where growers halted planting prior to last week’s cold temperatures to avoid cold injury risks.

After being underground for several weeks due to the cool weather conditions, early planted corn is starting to emerge in the southwest. Central and eastern Ontario should see emergence starting this week. It takes approximately 180 CHUs from planting to emergence of a corn seedling.


Soybean planting continues, but the range of progress across regions of the province varies widely (25-80 per cent). The average for soybean acreage planted in the province stands at around 60 per cent complete.

Heavy rain and ponding followed by warm, dry weather is a recipe for crusting in heavier soils that are low in organic matter and have little residue to protect the soil surface. Excessive tillage and tillage performed when soil is either too wet or too dry will decrease aggregate stability and increase the risk of crusting. Those producers with fields at risk who are anticipating emergence in the next couple of days should be prepared to monitor the situation and potentially perform a rescue operation. This is achieved with light, shallow tillage. “Crust busting” carries some risk of mechanical damage to the seedling. Plan this operation for the hot hours of the day when the seedling is less brittle, avoid the vulnerable “crook stage,” and operate the equipment in the same direction as the crop rows. If a field often requires a rescue like this, remediation with organic amendments, cereal (cover) crops and proper residue management is warranted.


Crop injury from last week’s cold snap was less severe than anticipated. However, concerns over crop health exist in areas where there has been very little growth and development over the last six weeks due to cold temperatures. As temperatures continue to climb, it is expected that those plants will begin to grow more rapidly and look better.

Winter wheat in southwestern Ontario is at flag leaf, while most of the rest of the province is at or approaching stem elongation.

Spring cereals continue to emerge, with most of the crop being at the 2-3 leaf stage. Weed control continues in these fields. With the warmer temperatures forecasted, it is expected that weeds and cereal crops will start to grow more rapidly.

If you are scouting cereal fields, please consider reporting Cereal Leaf Beetle observations through the survey available on under “Ontario Cereal Leaf Beetle Survey”. The CLB survey has been launched to collect baseline data that will help track the spread of CLB and develop solutions to manage this pest.


Like wheat, forages seem to have made it through the cold relatively well. The exceptions are mostly in fields that were cut or grazed late last fall. Alfalfa plants are weakened by late cutting, and spring conditions may not have allowed sufficient recovery for them to withstand the frost.

Flowering in grasses is linked to day length, while in alfalfa it is initiated by a combination of GDD accumulation (heat) and day length. This means that hay fields containing grass will mature at about the same time as normal. The cool conditions may result in lower-than-average yields of grass or mixed hay at first cut. Delaying first cut of mixed hay can improve yield by allowing more time for alfalfa to grow, but the rapid decline in grass quality will impact the quality of the forage.


Winter canola fields in Essex and Chatham-Kent are at or near white mould fungicide application timing and are fully in bloom. Other fields that are further north are a week or more from fungicide timing. So far, no insect pests have been observed in winter canola.

Spring canola planting is wrapping up and seedlings are emerging.


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