It’s been a trying spring to say the least.Over the passed two months, rainfall events have vastly outweighed the sunny warm days needed to dry the saturated ground making it more than challenging to find fit ground to plant the crop.
For those who are fortunate enough to have some of the 2019 crop planted can’t help but notice how far behind it is.Delayed planting is one culprit, but the other is the lack of heat that we’ve had to push this crop along.
Crop Heat Units (CHU) are a measurement of cumulative heat over the growing season. CHU’s are calculated on a daily basis using the minimum and maximum temperatures.Crop Heat Units begin to accumulate May 1 of every growing season and end with the first occurrence of a frost (-2°C) in the fall.
They are crucial in the development of both corn and soybeans and are used when selecting the proper maturing corn hybrid and soybean variety.If a corn hybrid is listed as a 3000 CHU, that means it needs 3000 CHU for it to reach its physiological maturity, or black layer.
Around Ridgetown, we have accumulated 698.3 CHU from May 1 to June 15 this season.Overall, we’re just over 115 CHU behind the 5-year average- a difference of almost 2.5 CHU per day over the course of 46 days between May 1 and June 15.
Seeing as a majority of the crop didn’t start to go in until the last week of May and into June, this comparison is irrelavent as the crop could not capitalize on these heat units. To get a better look, we’ll compare how CHU accumulated this year compared to the five-year average between May 25 – June 15.
Over this period, we’re about 53 CHU behind the five year average which is equivalent to about two warm days in late June. What is the significance of all this?With the late start to planting and receiving less CHU than the previous five years, there is some increased risk that the corn planted in mid June may not reach physiological maturity in September as it has in years previous.Let’s compare a 105 relative maturity (3175 CHU) hybrid planted May 15 to a 98 day (2950 CHU) hybrid planted June 10 in the Ridgetown area.
WIN’s growth stage model uses 30 years of historical weather data to predict growth stages for corn.As CHU accumulate, the corn progresses through the growth stages and the actual accumulated heat units adjust the model making it more accurate as the season moves forward.According to the model, the 3175 CHU May 15 planted corn is predicted to black layer October 1, while the 2950 CHU June 10 planted corn is set to black layer October 28.
Again, this is only a prediction based on weather trends we’ve seen over the last number of years.It’s evident that we need a hot summer and warm fall to finish the crop, but what other challenges do we face with this delay in crop maturity?
Disease and insect lifecycles are driven by heat and crop development.
Using the same growth stage model for corn, the 3175 CHU hybrid planted May 15 is estimated to tassel on July 21, and silk July 26.Conversely, the 2950 CHU hybrid planted June 10 is predicted to tassel August 4 and silk August 8. August is typically been one of the wettest months in the growing season.
If the corn advances through the reproductive stages in August, there is an increased risk of DON infection and other ear rots if we have high relative humidity and precipitation during the critical silking period.
Western bean cutworm is also driven by crop heat units and growing degree days (GDD).This pest needs around 730 GDD to emerge from the soil and peak flight is observed at about 790 GDD.Based on this insect model, peak flight is estimated to occur around August 8, versus the middle of July as we’ve observed in previous years.
Peak flight will occur regardless of the maturity of the hybrid chosen, but we need to be aware of the later planted corn as the WBC is attracted to pre-tasseled corn.
We’ve done the best we can with the conditions we’ve been dealt to get the crop in the ground.Let’s continue to manage to the best of our ability with what is left in the growing season to harvest.
There’s still plenty of management opportunities to push yield potential, from managing nitrogen, micronutrient deficiencies to assessing the need for fungicide and insecticide application and their timing.
As always, contact your local AGRIS Co-operative or Wanstead Farmers Co-operative crop sales specialist to provide insight on how to manage yield potential over the rest of the growing season.