For three days, from Aug. 1 to Aug. 3, temperatures hovered right at or over 100 degrees in the Lorane Valley. Smoke from wildfires burning far away nevertheless created a light haze that prevented the temperatures from breaking heat records as predicted. When the thermometer hits triple digits, the welfare of our workers and health of our crop are top concerns. In both cases, timing of the heat wave in the first few days of August was fortuitous.
After two months of having 90 to 100 workers in the vineyards, a smaller crew of 35 is working this week. Their days ended at 2:30 p.m. to beat the worst of the heat. Throughout the summer, and especially during periods of intense heat, the importance of hydration is emphasized along with reminders of how to recognize symptoms of heat stress.
If heat poses a danger to humans, how do grapes fare? Is there such a thing as too much sun for a ripening grape? We turned to Ray Nuclo, King Estate’s Director of Viticulture and Winery Operations, for answers.
The threat to grapes is not just the number on the thermometer but direct sun exposure. At a certain temperature – around 90 degrees – the grapes essentially shut down and photosynthesis stops. That means the grapes aren’t growing and aren’t accumulating sugar. Over time that would be cause for concern, but grapes can weather a few days with no problem.
Of greater concern is sunburn, or sun scald, especially in the hanging trellis systems, which are used on about 20%, or 90 acres, of the vineyard. Because the vines hang down, the fruit is on top of the trellis where it is more exposed to the midday and afternoon sun.
The upright growing trellis systems provide greater protection for the grapes in a couple of ways. First, while we trim the vine leaves back on the east side of the vines that get the weaker morning sun, we leave them on the west side where the vines bear the brunt of the afternoon sun. The leaf canopy provides some sun protection.
Second, most blocks had leaves removed early in the development of the fruit, and clusters that develop in sunlight tend to be more resilient to sun scald. It is the clusters that develop in the shade of the canopy and then are exposed late that tend to be more susceptible. Temperatures that were predicted had us worried that even clusters that developed in full sunlight might be in jeopardy, but the fact that actual temps are coming in a couple of degrees cooler is allaying those fears. As Vineyard Manager Meliton Martinez said, “So far, so good.”
During heat events like this one, King Estate’s location and climate are advantageous no matter the trellis system. At our altitude and with our marine breeze, we are on the cooler side of an already cool-climate AVA so the heat’s effect is less pronounced here.
Finally, we’re fortunate that the clusters haven’t been thinned yet. Crop loads are heavy and in the next few weeks our crews will go through and trim off excess fruit to optimize the quality of the remaining berries. Now when we thin we can trim off any sun-damaged berries, leaving the healthy fruit to ripen. The forecast for the rest of August calls for normal temperatures, and we are on track for harvest at the estate to begin in late September.