Thursday, July 16, 2015

Winter kill

I got a call from one of my fruit growing buddies early this week.

Roger had some health issue.  To be truthful, Roger had a LOT of health issues.  He had been in various assisted living situations for the last 18 months.

He moved back home about a week ago.  He had three months of grass to mow.  His zero turn had not gas.  He wanted to know if I could bring him five gallons.

Well, you darn betchya!

I also brought a chainsaw, loppers and work gloves.

He had two brutal winters of ice storms and winter kill.  I had to cut and drag brush before he could do a bunch of mowing.

What lived, what did not

In addition to ice storms we had two back-to-back winters with a low temp of less than -20F.  For us, those are test winters.

Not being here, his trees did not get fertilized, or sprayed nor was the sod "controlled" close to the trees.

A tree that has been stressed by cold temperatures has a mosaic of living and dead tissues.  The network of living tissue will span and bond together when growing conditions are good.  Often, a winter stressed tree is slow getting growing in the spring as adventitious buds are recruited.  When nutrient starved (see comments about fertilizer and sod) the tree will not bank enough carbohydrates to be at optimal winter hardiness for the next winter.  This is often not a big deal...but it is if the next winter is also a test winter.

Roger had about 50 big Carpathian Walnuts (Juglan regia).  Nearly all of them are dead or nearly dead.  It is a bit spooky to stand in the middle of a dead orchard.  The trees are planted on 40' centers and they had canopied over.  They are big trees.  And they are dead.

Sweet cherries: kaput.

Peaches:  10% survival

Pears:  No observations....I was not in that part of the orchard.

Sour Cherries and apricots: About 30% mortality.

Apples: About 25% mortality.  Of particular anguish, to Roger, were the trees that had 20 or more varieties grafted on them.  The current "best thinking" is to not graft more than two varieties on a given tree.  The chances of one of the varieties harboring viruses or being Typhoid Mary for fire blight goes up as the number of varieties increases.

While every additional component in the tree adds risk, I can see the value of having the backbone of the tree, the trunk and the main branches, be a variety with excellent fire blight and cold resistance.

Fruit growers from Alberta, Canada (-45 to -50 degree F lows) tell us that winter kill is most likely to occur on the sunward side of the trunk (usually Southwest side) at the snow line.  The second most likely place for it to occur is on the tops of main branches, close to the trunk.  Both of those locations experience a reflector oven effect where the surface of the trunk or branch warms up each day due to the sun loading.  The surface thaws...only to be flash frozen each night.  Hardiness typically increases through the early winter but those two areas can never build up peak cold resistance due to the thermal cycling.

One additional tip from the Alberta growers is to either paint the trunks (and tops of main branches on the south side of the tree) with white latex paint or to wrap with light colored newsprint.  Both of those techniques reduce the thermal cycling issue.  Note that protecting the trunk with black, corrugated plastic "sewer" pipe can be counter productive because it may protect against rabbits but increase thermal cycling.

The Alberta growers tell us that the cold hardiness of the TREE (as a system) is determined by the frame.  Choose that well and you will have few problems with winter kill.  I listen when folks from Alberta talk about armoring trees against winter kill.  They know what they are talking about.

Black walnuts, hickory nuts, persimmons, pawpaws, pecans:  No mortality.  Roger's property does not drain well and the persimmons were in standing water when I went there today.  All of these species can be found in flood plains so it is not surprising that they can survive occasional wet feet.

Asparagus and raspberries looked good.

I dragged brush for three hours.

I am whipped.

1 comment:

  1. I'm presuming this is our mutual friend, Roger M? Hadn't heard from him in a while- didn't know he'd been out of commission - but glad to hear that he's back home and riding the mower!
    Sad to hear of the mortalities in his orchard... but bless you for helping him.
    Have a cold one and put your feet up; you've earned it.