What Happens If My Winter Wheat Did Not Emerge 

The fall of 2011 was extremely dry in many areas of Manitoba.  Reports of winter wheat germination and establishment ranges from very good to very poor, dependent upon amount of precipitation received after seeding.  Some areas have reported seed that has yet to emerge or stands that are only at the 1 to 2 leaf stage.  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). 

 

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

 

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

 

Poor emergence or plant stands are leaving many producers wondering if their winter wheat crop will survive the winter and what type of stand they might expect in the spring.   We don’t have a crystal ball to look into the future but we do know that winter wheat needs to undergo two important physiological changes in the fall – cold acclimation and vernalization. 

 

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. 

 

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. 

 

If at the time of publication there is minimal snow cover, scout your winter wheat fields and record the crop’s condition such as crop stage and stand.  Over the winter months, take note of winter stresses such as cold snaps, when they occurred and their duration.  And lastly, note the length and timing of snow cover.  For winter survival, February/March snow cover is the best.  These notes will help you with spring assessment of winter survival and crop life.

 

Source:  Winter Wheat Production Manual, Brian Fowler, 2002.