Well, quite a bit if you are in Oklahoma apparently.  On Feb 10 the low recorded in Stillwater was -19F.  One week later it was 81 F.  The question still remains how much damage was done by the cold temperatures.  I have reports of blackberry buds being dead, but so far I have not been able to look at the grapes — Monday is the day when I will get that chance.

Are we in danger of having budbreak soon with all of these warmer than normal temperatures?  Some reports in the literature claim that 5 consecutive days that average 50+F (high + low/2) will lead to budbreak.  Right now we are looking at 4 in a row in Stillwater and the forecast will get us to 5 and maybe 6 or 7.  The chilling requirement has been met (vinifera grapes don’t require much chilling anyway).  So, will they break bud next week?  A couple of reasons the answer to that is no.  One, the weather will turn cooler again and slow down the process.  Another reason, and an overlooked one I believe, is day length.  The days are just not long enough yet.  I have a working hypothesis that the vines will need at least 12 hours of day light to start thinking about breaking bud.  Research has shown this to be true for American grapes, but I think it is also true for vinifera.  The timing of budbreak is very complex, with genetics and environment playing critical roles.  Chilling, heat accumulation, and day length are all players interacting with genes within a specific cultivar.  I think the vines will remain quiescent (the chilling requirement has been achieved and the vine is just waiting for heat accumulation and day length to start the growth process) for a few more weeks.

I will report on my damage findings next week.

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