How Many Days Until My Grain Corn Reaches Maturity?

The 2016 season has seen normal to above normal accumulation of corn heat units (CHU), with a range of 95 to 117% of normal from May 1st to August 14th: Percent of Normal Accumulated Corn Heat Units. So as we inch closer to September, producers start to wonder when their grain corn may reach physiological maturity (R6).  At this stage, kernels have reached maximum dry matter accumulation and kernel moisture can range between 30 to 35% (but can vary by hybrid and environment).  But more importantly, at physiological maturity the grain corn crop will be safe from a killing frost.

The following table was modified slightly from the original table found in NDSU’s Crop & Pest Report August 8, 2013.  The table relates calendar days to corn kernel development and yield in general terms.

Table 1: Relationship between corn growth stages and calendar days to maturity, yield loss, and other kernel characteristics

Days to Maturity Grain Corn

Source: NDSU Crop & Pest Report – August 8, 2013

The ranges listed are fairly large in order to take into account variances in temperature (climate) and the relative maturities of the hybrids grown (genetics).   It is also important to remember that the various plant stages and the duration of those stages can also be influenced by soil fertility, cultural practices (plant populations) and water availability (dry conditions can hasten maturity).

Source:  NDSU Crop & Pest Report August 8, 2013 http://www.ag.ndsu.edu/cpr/plant-science/characteristics-of-late-maturing-corn-08-08-13

Submitted by: Pam de Rocquigny, Provincial Cereal Crops Specialist, Manitoba Agriculture

Manitoba Agriculture website: www.manitoba.ca/agriculture
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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 http://www.gov.mb.ca/agriculture/crops/production/grain-corn/index.html
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June Seeded Canola – How to Reduce Maturity (but Not Sacrifice Yield)

Canola is an extremely adaptable crop that will still profit when seeded in June, but you need to work with what you have! 

Reduced Yield Potential – June seeded is lower yielding that May seeded canola, but the yields will still be there. Plan accordingly though, instead of the 45 bu/ac expectation, back it back 10% to 40 bu/ac and fertilize accordingly (if fertilizer is not already on)

 Table 1: Seeding Date and Yield Potential for Canola by Manitoba Region (MASC)

Seeding Date (week:month) %YIELD (Province) SW Central NW RRV


04:04 103 105 105 104 105 95
01:05 105 102 106 119 105 108
02:05 106 102 104 105 102 105
03:05 102 102 100 104 101 103
04:05 93 95 94 85 98 94
01:06 86 90 87 80 89 90
02:06 78 79 84 85 70 88
03:06 68 70 75 81 67 81


Faster Crop Development – Canola growth and development if based on Growing Degree Days (GDD).  Seeding in June means they add up faster, so May 5 seeded canola (with a cool May) may take 105 days to mature, but a June 5 seeded canola (with a normal June, July, August) could only take 95 days.  In 2014 we are seeing this.  Canola is emerging in 5 day, showing its first true leaf in 10 days and 2nd leaf in 14 days.  This is to our advantage!

Know When First Fall Frost Is – see http://www.gov.mb.ca/agriculture/weather/agricultural-climate-of-mb.html.  Calculate for your area when the first fall frost is expected and backtrack to days needed for canola to get to 50-60% seed color change (about 80 – 85 days).

Use Agronomy to Reduce Maturity (and maintain yield):

These tips can help reduce maturity, they may not be exactly the day indicated, but they will help shave off a few days:

  • Seed shallow: if the moisture is there, target 1/2 inch vs. 1 inch, this can save 1 to 2 days
  • Increase seeding rate: more canola plants means more crop competition between plants, less branching and faster maturity.  The extra plants will make up the yield.  Bonus is flowering and swathing timing will be more even across the crop as well.  Increase seeding rate from 3 lbs to 5 lbs and save 1 day.
  • Put phosphate with the seed: Don’t skimp on this, especially if you know your fields are typically lacking.  Phosphate is important to the early root development and establishment of the plant which helps with maturity later on.  Add you phosphate and don’t go backwards in maturity to save 1 day
  • Add only the nitrogen you need: Excess nitrogen means excessive early vegetative growth which slows down the development of the crop.  Only add what you need and don’t go backwards in maturity or potentially save 1 day.
  • Switch your variety: This may be a no-brainer, but switch to what? See www.seedmb.ca, page 58 or paper guide page 58 to see what your options are.  Also talk to your retailer and seed dealers about what they have (or can get)

You can also give us a call at the Crops Knowledge Centre for more information 204-745-5663


Submitted by Anastasia Kubinec, MAFRD Oilseed Crop Specialist

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What Should My Soybeans Look like when they are Ready to Harvest?

Prepared by Dennis Lange, MAFRI Farm Production Advisor (Altona)

For new growers knowing when soybeans are ready to harvest can be difficult.  Driving by the field, you may think that it is ready to harvest, but on closer inspection you may find plants that still look yellow to green instead of tan to brown. If your entire field has a greenish tinge or a majority of plants in the field once you walk in look green, your beans would not be ready to harvest.  If there is only a few plants that look like this, you may be ok or this might represent only a low spot or less advanced spot in the field. 

Note the green stem in the group of brown stems


This Field is 5 – 7 days away from harvest (credit: D.Lange, MAFRI)

The soybean plants and pods when mature, should be brown or tan in color and the seeds should rattle in the pod.  When the crop is mature and ready for harvest the seeds would be oval shape and firm.

Seeds on left are ripe and ready to harvest, seeds on right are green and not ready to harvest

Once the combine pulls into the field check the moisture which should be below 13%. The Canadian standard for safe storage is 14% moisture, however soybeans going into the USA require 13% moisture and since a large portion of the soybeans do go into the USA  it best to keep below that 13% level.

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