Thank you Blake Leja and Peter Plaehn for your responses on Lindsay Brown last week, much appreciated!
This week: Rain
How can the timing of rain during the growing season impact fruit quality? Specifically describe important periods of the growing season and the causes, effects, and resulting actions that can be taken by vineyard managers in response to rain (or lack of it).
Ok, complicated question. As I understand it (and someone please chime in):
-Rain in spring can invigorate bud growth and provide nourishment for early shoot development. The threat here is low temps that can cause frost or mildew pressure, causing issues with bud break and/or fruit set and thus affecting yield at the end of the season. One school of thought dislikes spring rains as it causes too much vigor too early in the growth cycle. Either way, airflow is critical to avoid disease. Other issues from spring rains can include incomplete flowering and shatter.
-Rain mid-summer is usually not an issue as long as spring wasn't too wet and it's not followed by a wet harvest. Ongoing issue of managing vigor and the vine's allocation of resources.
-Rain during harvest can doom an otherwise good vintage. Picking before a coming rain can result in not fully ripe grapes, and picking after can yield diluted grapes with low acid levels. In 2013 in Oregon this was key: picking before the rain at normally warm sites ended up being fine, but still with more acid than typical; those on cooler sites had underripe wines. Those that waited out the rain (7 days of it) had sunny skies afterward and had time to let the grapes dry out and made good wines, though the whining and gloom of those who picked early overshadowed those who looked at a weather forecast and waited. :-)
-If none of the above happens and it's a dry/drought vintage, one or two years don't have major effect on vineyards. More than that, though, starts to impact vigor (potentially positively, depending on location) and fruit set because the vines are starved of moisture. Refer to the irrigation discussion from two weeks ago for that topic.
In fact checking some of this, I found this article (supposedly posted 12/31/69, pre-internet??) that covers some of these topics: