As we enter the home stretch of the 2017 growing season it is fair to say that we have had an interesting growing season so far. The Pacific Northwest experienced one of the wettest Springs on record with enough rainfall to fill up the region’s reservoirs and subsequently eliminate any drought watch we’ve had over the past 4 years. The generous Winter/Spring precipitation filled up our soils with moisture allowing for great canopy growth across the Northwest. The unusual over-sized canopies will result in several consequences on the 2017 growing season.
First, large canopies create shading which combined with mild spring temperatures have invited an increase of powdery mildew, aka rot, pressure. We are now getting out of the Powdery Mildew danger zone and growers that were not on top of their mildew sprays have likely suffered greatly. Also, I would not be surprised if we also discover significant Botrytis pressure at harvest especially if the Fall is wet with conditions for primary infections (cool temperature, humidity in the canopy) as were present in the Spring. These canopies are still active, in Oregon in particular, which makes hedging and trimming tricky. We’re finding that removing shoot tips promotes lateral bud growth increasing further congestion in the canopy and promoting rot risks.
Secondly, large canopies mobilizing resources combined with the high crop last year seemed to have moderated the 2017 crop load somewhat and we will likely see a slight drop in yield in 2017 versus 2016 (in the 5 to 10% range).
At this point my main worry is dark and humid conditions inside the canopy which will be especially challenging in September as they will lead to an explosive grey rot situation. We could also see collateral damage with a reduction of fruitfulness in 2018 due to excessive shading on basal buds that are being formed this year and are therefore pre-programming next year’s growing season with clusters. Indeed vine buds that are illuminated in one year tend to pre-program more clusters in them than buds that are shaded; it is almost as if the vine reacts to shade by producing more vegetative growth the following year as a way to get ready to “grow out” of the shade .
A couple additional thoughts on big canopies in 2017. A smaller crop than usual as estimated above paired with large canopies could accelerate harvest because there is more photosynthetic power to ripen less grapes. That would mean an early harvest with potentially high sugar levels presenting winemaking challenges. The added canopy coverage could be welcome though considering the potentially record breaking August heat that we have in the forecast as it will protect clusters from sunburn – so not all negative.