We are wrapping up a particularly hot July. The last time I had to write about heat stress was 2022, so this year seems to be making up for 2023’s persistent coolness. We all remember 2022. We had a couple hot days in late June that did quite a bit of damage in some vineyards. Then in late August, the sun parked itself right on top of California for three weeks, frying everyone’s hope of a decent harvest.

This year, the heat has come earlier and hasn’t quit. One measure Mark Greenspan and I like to look at is amount of time temperatures exceed 100°F and 105°F thresholds. Anything over 100 usually slows down vine growth and metabolism. Anything over 105 causes serious damage.

Here’s a comparison of 2022 and 2024 so far in the Russian River Valley.

And here’s Calistoga…

At least in Calistoga, 2024 is just a shifted version of 2022.

Now, these are ambient air temperatures. Fruit exposed to full sun can be as much as 15°C (27°F) over ambient temperature, which we initially found hard to believe, but there are numerous studies indicating this. Many of you got there this month. Some growers have experienced complete crop loss due to sunburn and shrivel. Tissue temperatures above 50°C (122°F) causes oxidative stress and cell death leading to the telltale signs of sunburn. This kind of extreme heat can also denature the proteins responsible for fruit maturation. This fruit may look alright immediately following the heat event, but it will never catch up in terms of color or maturity. We’ve all seen those pink berries that never really fully color up.  The good news, if there is any, is that this fruit can be easily eliminated in late-season thinning passes as it looks very different from unburned fruit. I recommend leaving it as a physical barrier that can protect your remaining fruit until the survivors are fully through veraison.

But what about this remaining fruit…if you have any. Unexposed, shaded fruit is usually on par with ambient temperature. Ambient temperature is still really hot. What does an early and prolonged heat wave mean for the surviving vintage?

Read the rest of the article here.

Putting together budgets for next year?

How about investing in soil moisture and weather monitoring? 

Soil moisture probes allow you to see how much water you have in the soil and how deeply each irrigation goes. If you want to water less or water more efficiently, probes can help you do that. 

How hot did it get at that mountain vineyard everyone forgets about? How are growing degree days stacking up with respect to your valley floor vines? Get yourself a weather station and have all your vineyard weather data available at a glance. Get frost alerts or heat notifications when it's time to call the crews in. 

email loni@advancedvit.com for more information.

Heat Wave