Winter Wheat Survival – Impacted by Fall Management Decisions & the Weather!

For winter wheat, survival through our cold Manitoba winters is directly influenced by fall management decisions, including variety selection, seeding date and depth, adequate plant stands, fertility and stubble height/density. Optimal winter survival can also be influenced by fall weather conditions and snow cover.

What is the ideal situation heading into the winter?

  • Plant stage would be at the 3 to 4 leaf with 1 to 2 tillers, and well developed crown tissue.
  • Cool conditions in the fall, where plants would grow for 4-5 weeks, followed by 4-8 weeks (October to November) of growth that allowed plant to acclimate (harden off) and vernalize (giving the plant the signal to flower next spring).
  • A minimum of 4 inches of trapped snow cover through December to early March to buffer soil temperature changes and provide protection to the crown tissue.

What is cold acclimation and vernalization? 

Cold Acclimation. The ability of the winter wheat plant to survive the winter often depends on its ability to withstand low temperatures.  Under normal field conditions, eight to twelve weeks of growth is usually required for the full development of winter hardiness.  The first four to five weeks is a period of active growth that takes place when average daily soil temperatures at a depth of two inches (5 cm) are above 9°C. Both the cold acclimation process and winter survival require energy and this period of warm temperature allows for the establishment of healthy vigorous plants. Plants with well developed crowns before freeze-up are most desirable.  However, plants that enter the winter with two to three leaves are usually not seriously disadvantaged.

Cold acclimation of winter wheat plants begins once fall temperatures drop below 9°C.   In the field, four to eight weeks at temperatures below 9°C is usually required to fully cold harden plants. However, regardless of the amount of cold acclimation, the wheat plant must receive insulating snow cover to survive the cold prairie winters.

Vernalization. During the period of cold acclimation, the low temperatures also initiate in the plant a physiological response called vernalization.  During vernalization, the plant converts from vegetative to reproductive growth and the reproductive structures are developed.  Because of this vernalization requirement, winter wheat produces only leaves for both the main stem and tillers aboveground in the fall in preparation for winter.  The growing point and buds of both the main stem and tillers remain belowground, insulated against the cold winter temperatures. Once vernalization requirements are met, the growing point differentiates and develops an embryonic head.  At this time, wheat head size or total number of spikelets per head is determined.  What is important to note here is neither seedling growth nor tillering is required for vernalization to occur.  This process can begin in seeds as soon as they absorb water and swell.  Hence, late planted wheat that has not emerged prior to winter should be adequately vernalized.   Or in extreme conditions, vernalization may occur under cool spring conditions.

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

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What are my options if my winter wheat does not germinate this fall?

Poor emergence or plant stands are leaving many producers wondering if their winter wheat crop will survive the winter, what type of stands they might expect in the spring, and whether the crop will undergo the necessary processes to produce a head next year.   Unfortunately at this stage there isn’t much that can be done except understand the potential impact to crop production if the crop didn’t emerge or has just emerged.

The stage of crop development in the fall influences not only winter survival and yield potential but also crop competitiveness, maturity and the risk of infection with diseases such as rust and fusarium head blight (see Table 1 below).

Table 1:  Potential impacts of fall growth stages on winter wheat production factors

Growth Stage

Date of Germination

Yield Factor

Competition Factor*

Relative Maturity

3 leaf & tiller

Sept 5

100%

5

0 days

1-2 leaf

Sept 15

90-100%

4

+ 4

Sprouted

(not emerged)

Oct 1

80-100%

2

+ 8

Not germinated (imbibed)

Oct 15

60-100%

1

+ 10

* Competition factor: 5 = most competitive, 1 = least competitive

As the table illustrates, there may be minimal impact to yield potential of a crop that didn’t emerge in the fall but maturity will likely be delayed.  Crop competitiveness may be decreased so early season nitrogen application to encourage tillering, as well as timely weed control, will be very important.

In regards to vernalization concerns and whether the crop will produce heads next year, the key points to remember are:

  • Neither fall seedling growth nor tillering is required for vernalization to occur.  This process can begin in seeds as soon as they absorb water and swell.  Hence, late planted wheat that has not emerged prior to winter should be adequately vernalized.
  • Vernalization may also occur under cool spring conditions.

If next spring winter wheat fields whose stands are extremely variable with large patches of dead or weakened plants, replanting may become a more realistic option.  If you are considering reseeding and before destroying any wheat fields, you will need to contact your local MASC insurance agent.  For more information on winter wheat insurance information, please visit MASC’s website at: http://www.masc.mb.ca/masc.nsf/program_winter_wheat.html

There are numerous articles on MAFRI’s site dealing with dry conditions and poor germination, including “What Happens if my Winter Wheat did not Emerge?”, “Spring Germinating Winter Wheat” and “Concerned About Your Winter Wheat Stand?”.  For more information on winter wheat production, please visit MAFRD’s website at: http://www.gov.mb.ca/agriculture/crops/production/winter-wheat.html

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

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