14-Jul-09 09:15 | Eric Stafne

I was out in the heat yesterday afternoon at Perkins.  My handheld infrared laser thermometer indicated the ambient temperature was 45C (113F) in the vineyard.  Becky and I measured canopy temperatures as the vines were being irrigated from 2pm to 3:40pm.  I have not had a chance to statistically analyze the data yet, but there seemed to be a difference on which side the measurement was taken (east vs west).  The leaves of the irrigated vines varied in temperature, but they were always less than the ambient temperature, in some cases much less.  Fruit clusters in the shade were on average about 5C higher than the canopy temperature.  Clusters in the sun approached ambient temperatures.    The vines I was measuring were Chadonnay on different rootstocks, so it will be interesting to see if rootstock made a difference.  I will also do this on a day when we don’t irrigate the vines to see what happens then as well.  The question becomes, can we decide when to irrigate with this method?  A few papers have been written to discuss this along with the problems of making a useful model.  This also might be a method for choosing genotypes with heat and/or drought tolerance in a breeding program.