Saturday, March 17, 2018

Drought Effect on Grape Vines

So 2017 was an amazing year for heat, we had about 1100 degree days celcius of heat which is about the most we have ever had. The problem was we didnt get any rain, really, no rain for 3 months. The final rain in the sping was about 1 cm on June 14th and we didnt see any more rain until September 15th. The vines suffered tremendously in the heat and water stress. Here is a picture of drought on grape vines (not from Arrow Lakes Vineyard).

Arrow Lakes Vineyard irrigates each vine but only as sustenance watering as we embrace the climatic nuance that is imparted on wines by the year to year variance in weather. Given the extreme of the 2017 drought period irrigation was only capable of keeping the established vines from perishing. Even with watering, we lost some of the new Castel vines planted this past year as they didnt have established root system able to support the vine in the heat. So there were positive and negative results from the drought. Some bennefits of the water stress was a higher than normal sugar accumulation in grapes and reduction in malic acid more than normal from some varieties as they matured earlier with a smaller crop than usual. For some varieities I'd say 2017 was a great growing year as this translates into production of wine.

It was also interesting to see what vines flourished even under these conditions. For instance, most of the Kulhmans did ok (Leon Millot, Foch, Triompe), Castel also did ok, but Colmar did not, nor did Marquette. For white varieties, the Evangeline, Ravat, and Petite Milo did well but the L'Acadie and Seyval struggled.

The damage that concerns me is that which you can't easily see. What Im talking about is the physiological damage to the vine that does not readily appear as wilting leaves, small sized grapes, or stunted cane tip growth etc. Two things of concern are the vine health going into the fall and into dormancy and the bud developement that occured during the drought period. Both of these are going to affect the next years (2018) crop.

So with such a drought and accompanied vine stress the vines ability to both produce carbohydrates and uptake nutrients during the growing season are impaired. As the vine prepares for winter it transfers the carbohydrates to the canes, roots and also the grapes (as sugar). So the concern is that there is less production of carbohydrates that get stored and the vine does not have the normal amount of carbohydrate reserves for bud break in the following spring. We can't do too much about that except ensure we dont over crop the vine in the spring. We usually leave a few extra buds per foot of trellis until danger of spring frost has past but we may decide to forgo that this year so we don't short the buds we plan to keep of the necessary carbohydrates they need.

The second concern is around the bud development. So the buds that will be producing canes with grapes this year come from buds that were formed on the canes grown the year before. So last years canes that developed during the drough may have buds that are less developed or have less fruitful buds due to the vine stress and lack of nutirents avaialbale during thier formation. In particular, the buds that develop further up the cane, as the drought became more severe over the summer, likely suffered development problems due to low nutrients and vine stress. So for last years canes, the buds that developed at the start of the season, say the first 2-6 buds on the cane in advance of flowering time are likely to have a higher bud survival rates and greater fruitfulness than buds further up the cane. This is not just my supposition, there is a 2016 Cornell University report that supports this. In contrast, in a normal season its often the buds further up the cane, say from bud number 6-12, that are most fruitful.

So here is the thing, we often prune our vines with long canes of up to 12 buds, but if the buds further up the cane are dead or low in fruitfulness then our crop will be poor.  So for this year we will be going to spur pruning on many of the varieties. We will also leave an extra bud at the vine head for renual canes in case we want to go back to long cane pruining the following year.