Estimating Date of Grain Corn Maturity from Silking Stage

The 2015 season has seen relatively normal accumulation of corn heat units (CHU), with a range of 92% of normal to upwards of 111% of normal as of July 19th. According to Issue #12 of the Manitoba Crop Report, grain corn ranges in development from late vegetative stages to silking (R1).

Silking marks the start of the reproductive phase of development and begins when the silk becomes visible outside the husk and pollination occurs. Each silk is attached to an ovule which will become a kernel if pollinated. The CHU accumulation from planting to silking is about 50 to 55% of that required for the plant to go from planting to physiological maturity.

While this could be used as a general guideline, temperature and relative maturity of the hybrid must be taken into consideration. Plus, the duration of each stage during grain fill can also be influenced by soil fertility, cultural practices (plant populations), and moisture.

If we consider CHU accumulation and maturity rating of the hybrid, we can calculate the number of corn heat units required for a crop to pass from silking to physiological maturity. As mentioned above, the period from planting to silking takes approximately 50 to 55% of the total heat units required for the crop. Therefore, the remaining 45 to 50% would be needed to carry the crop from silking to physiological maturity. The table below identifies the approximate CHU requirements to bring a corn crop from silking to physiological maturity based on a range of CHU maturity ratings.

Table 1: Approximate Corn Heat Unit (CHU) Requirements from Silking to Physiological Maturity for Various Hybrid Maturities.

CHU Rating of the Hybrid Approximate CHU Required from Silking to Physiological Maturity
2100 945 to 1050
2200 990 to 1100
2300 1035 to 1150
2400 1080 to 1200
2500 1125 to 1250
2600 1170 to 1300


Once a crop’s CHU requirement from silking to physiological maturity is determined, the next step is to establish the number of CHU that can reasonably be expected from the date of silking until the end of the season.  Referring to Tables 2 and 3 (where dates of expected additional CHU accumulation from two silking dates in the season), we can estimate the approximate date when a given accumulation of CHU past silking is reached.

For example, if the silking stage of a 2200 CHU hybrid grown near Morden occurred around July 18, the crop would require approximately 990 to 1100 CHU to go from silking to physiological maturity (see Table 1 and use 1100 for simplicity).  According to Table 2, the accumulation of 1100 CHU starting July 18 would occur by approximately September 5 in Morden.  It is important to keep in mind that these numbers are estimates based on historical observations.  Some years will have temperatures above or below average, causing the dates to shift forward or back.

Table 2: Date of Expected CHU Additional Accumulation from July 18 at Various Manitoba Locations (Source: Environment Canada averages 1971-2000).

From July 18 +900 +1000 +1100 +1200 +1300
Brandon 31-Aug 07-Sep 14-Sep 25-Sep 10-Oct
Elm Creek 28-Aug 03-Sep 09-Sep 17-Sep 27-Sep
Emerson 26-Aug 31-Aug 06-Sep 12-Sep 19-Sep
Morden 26-Aug 30-Aug 05-Sep 10-Sep 17-Sep
Portage 28-Aug 03-Sep 09-Sep 17-Sep 28-Sep
Selkirk 26-Aug 31-Aug 06-Sep 12-Sep 21-Sep
Starbuck 29-Aug 04-Sep 10-Sep 17-Sep 28-Sep
Steinbach 28-Aug 03-Sep 09-Sep 16-Sep 26-Sep


Table 3: Date of Expected CHU Additional Accumulation from July 25 at Various Manitoba Locations (Source: Environment Canada averages 1971-2000).

From July 25 +900 +1000 +1100 +1200 +1300
Brandon 12-Sep 22-Sep 05-Oct 01-Oct
Elm Creek 08-Sep 15-Sep 25-Sep 08-Oct
Emerson 05-Sep 11-Sep 18-Sep 28-Sep 12-Oct
Morden 04-Sep 10-Sep 17-Sep 26-Sep 09-Oct
Portage 08-Sep 16-Sep 26-Sep 12-Oct
Selkirk 05-Sep 12-Sep 20-Sep 01-Oct 24-Oct
Starbuck 08-Sep 16-Sep 25-Sep 09-Oct
Steinbach 08-Sep 15-Sep 24-Sep 08-Oct


Remember that this is only estimating time from silking to physiological maturity, not when harvest can start.  Field dry down rate from physiological maturity to start of harvest is influenced primarily by weather factors and, to a lesser degree, by hybrid characteristics.  In simple terms, warmer temperatures and lower humidity encourage rapid field drying of corn grain.  Because moisture loss is greatest just after physiological maturity, both because the weather is usually warmer and because wet kernels lose water more easily, it stands to reason that a corn crop that matures earlier in the season will dry down faster than a crop that matures later in the season.

Submitted by:  Pam de Rocquigny, Provincial Cereal Crops Specialist, MAFRD

For more information on corn production, please visit MAFRD’s webpage at
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Warm Soil Means Fast Emergence….So Go Scout!

With most soil temperatures across Manitoba averaging over 10C, and the good soil moisture, crops planted are emerging quickly!

So, great news, but what this means is it is time to get out and start scouting!

Things to look for are:

  1. Emergence, plant stands, patterns in field – this can indicate if seeds planted evenly, but can also you could indicate early issues like cutworms, soil-borne disease and herbicide residue injury.
  2. Weeds species, numbers and size – if you crop is coming up this fast, so are the weeds!  Targetting the weeds when they are small and knowing the species so you can choose the right product and the right will really help with the control.  Make sure those little yield-robbbers don’t get to use the sun, moisture and fertilizer instead of your crop.
  3. Insects – cutworms were mentioned before, but more look more specifically for the damage on the plants if you can’t see the insect, as that can help with identification.  Are leaves clipped off leaves at or above the soil vs. chewed with ‘shot-gun’ hole marks in leaves.  Keep in mind the economic thresholds for control!
  4. Other funny stuff ?  Keep these in mind too when out scouting and mark down spots (or GPS tag) to monitor as the days go on to see how they progress, sometimes it takes a couple of days before things become obvious.  When in doubt give the Crops Knowledge Centre a call at 204-745-5663.

Submitted by: Anastasia Kubinec, Oilseed Crop Specialist, MAFRD Crops Knowledge Centre.


MAFRD Guide to Crop Protection:

Weed Identification:

Insect Identification:




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Should I Still Be Concerned About a Spring Frost?

Spring frost is something that producers need to consider into late May and in some areas of Manitoba, there is an elevated risk of occurence into the month of June.

Average Date of last Spring Frost – is considered after May 19th.  In the  Portage la Prairie, Langruth, Pilot Mound, Morden and Altona regions there is less than a 50 percent chance that frost will occur after the 19th. In other areas, the last spring frost occurs, on average, after May 24. On higher elevations, central Interlake and the south-eastern regions of Manitoba can expect frost during the first week of June in one out of every two years.  Figure 1: Manitoba Average Last Spring Frost

1 in 4 year risk– that the last frost will occur about eight days later than average. This means a 25 % risk that the last spring frost will occur after May 24 in the Portage la Prairie and Altona regions. In most other regions of Manitoba, a 25% risk of a spring frost in the first week of June and in the Riding Mountain and Hodgson regions, that is will occur later than mid-June.  Figure 2: Manitoba Last Spring Frost (1 in 4 years)

1 in 10 year risk – a 10% risk that the last spring frost will occur later than June 3 for most regions.  A recent example of this is in 2009, when there was a wide spread frost through the agricultural growing region on June 6th.  Figure 3: Manitoba Last Spring Frost (1 in 10 years)

If a frost does occur, please refer to MAFRI`s Spring Frost Damage Bulletin to help assess the situation at

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