Thursday, 11 February 2016

Black Sea weather forecasts elevate risk of winterkill

Next week’s central Russia weather forecast is showing day time highs of +6C and night time lows of -6C while further south Stavropol is showing +18C by Thursday.

Long term average lows in central Russia can still drop to well below -10C in February and below -5C in Southern Russia.

With that in mind I thought it might be useful to look at the physiology of winter kill in wheat.

Winter mortality can be caused by a number of factors either in isolation or combination and is essentially the air or soil temperature falling below a critical level for a particular cultivar.

In the autumn, crops can be at risk if they are late emerging or the temperature drops suddenly before the plants have had sufficient time to harden off.  This may be an issue in south and east Ukraine this year as dry conditions delayed emergence there.

Plants can succumb to cold induced desiccation when they are exposed to long periods of cold without adequate snow cover.  I don’t believe we have seen any regions this winter that have had exposed plants for long enough but then again it depends on the definition of long enough.  

We have certainly seen plants exposed to cold temperatures in January ahead of snow falling and while it might not have resulted in plant mortality it may have caused leaf death reducing green leaf and yield potential and parts of Ukraine are currently snow free.

Prolonged periods of very low temperatures below -15C will weaken and ultimately kill off plants but we have not experienced conditions like that this winter or for some time now.

Ice encasement can result in plant mortality fairly quickly even if air temperatures don’t get all that low.  Ice freezes the leaves causing intracellular ice to form which ruptures the cell causing mortality.  Furthermore plants can be deprived of oxygen and suffocated.  We are currently seeing conditions like this across parts of central Russia as reported in yesterday’s post.

Then there is mortality caused by alternate freeze thaw action which can cause increased injury from ice crystal growth with each freeze cycle.  This is what we might be looking at in central Russia as we go in to next weeks plus minus scenario.  Further south there is a possibility of freeze thaw damage if temperatures drop to below freezing from the forecast double digits but more likely it will be plants softening off in the warm weather or a combination of both that could cause problems.

To keep this all in context I don’t see an imminent or actual catastrophe but neither do I see a completely problem free situation. 

What the weather does now as we enter that final period of winter will be critical as there are a couple of scenarios that could play out and result in elevated levels of winter kill this year.