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.