>The air temperature now at 6:30 PM in northern Minnesota is +8 F. >The ground temperature under 15 inches of snow is now +27.3 F. Quite >a difference for plant survival. I have the sending unit of a >wireless thermometer in a plastic baggie on the ground surface >covered with 15 inches of snow. The coldest ground surface I >monitored was +18.1 F when it was -34 F a few weeks ago. The weather >this winter hasn't been really cold and we don't have much snow. The >winter temps have been gradually getting higher. Hard to say if this >is a long term or short term warming. Might be just a temporary >warming. A blip. The coldest I have seen it here was -48 F. I was >told this is now 3 ft of frost in the ground. Under the frost level >the soil is above freezing. Any moderately hardy plant should be >able to live under the snow at ground l
evel. Above the snow is a >rigorous, killing environment. When it is -40 F you often hear big >trees boom when their trunks crack. Last year a big bur oak next to >our house cracked. It had 140 growth rings. >Winter finally got it.
>
>"Ernest Plutko"
Ernest,
As cold as +18.1 F is to you in Minnesota I would wonder if this would be enough to kill the apple codling moth?
Comparatively speaking I have also been doing readings where it's colder longer of Fairbanks in the State of Alaska. In my case I used a mechanical insertion thermometer and I found -1 F at about 2.5" below the soil underneath at least 20" of snow and this occurring March 21, 2007 in -25 F ambient conditions. Being curious I also went to the hills finding soils averaging 6 F more. Whether in the hills or not this is apparently mild enough to many of the woody fruits not just apples. There are some plums and even some unconfirmed reports that I have heard of Siberian-C peach offspring of the type that Jim Fruth had alluded to recently... https://lists.ibiblio.org/sympa/arc/nafex/2008-February/023136.html (although I have to admit they may not have managed to make actual peaches on them yet.)
R.F. Hollaus (in zone-1 for Alaska)
[NAFEX] Insects vs. orchard Ground temperatures,
R F Hollaus, 03/01/2008