Over the weekend of May 16-17 this year, we experienced a brief but significant heat spike. Our vines had begun flowering the previous week (less than five percent), and temperatures had ranged from the 70s to the low 80s throughout the week.

As the mercury approached high 90s F., the vines had moved into full bloom. Grapevines are rather vulnerable during this period and require moderate conditions for complete pollination. Extremes of cool, hot, dry or wet weather can interrupt the process.

A good synonym for a vintage is “weather pattern.” Each growing season is a collection of fog and heat and wind and rain events. As wine grape growers, we can’t control the weather, but we do try to react to it in an appropriate manner to obtain the end product we want.

This year, as in 2007, the heat and subsequent rapid and incomplete flowering gave us little shot berries and shatter – when less than ideal conditions cause the vines not to pollinate and the flowers don’t become berries.

Within the considerable variety of Pinot Noir clones and selections in our estate vineyards, there are some variations in fruit set, but we’re seeing lots of loose clusters and small berries. The combination of large and small berries in our Old Wente selection of Chardonnay is often referred to as “hens and chicks” or even “pumpkins and peas.” It’s said that there may be a fertility issue in Old Wente with zinc as a player, but we find micronutrients are generally not a concern.

At any rate, if we were only concerned with yields, with crop tonnage, shatter might be a big negative, but instead we are excited. As in 2007, this could be the making of an excellent vintage quality-wise. Loose clusters and small berries can translate into more even ripeness, a low probability of rot due to increased air flow, and higher skin-to-pulp ratios in the berries which concentrates flavors and aromas.

Most of June was mild and uneventful with a small heat spike at the end, and July has been similar, although we have had high 90s during this past week. Our relative humidity has been good as well.

Ten days ago as I walked the vineyards, I saw no signs of virus showing. A few days ago after some heat stress, it began to show up. I’ve also seen the first signs of color (veraison), but it’s less than one percent of the crop. It will be interesting to keep track of how many days it takes to reach 25%, 50% and 90+%.

With more humidity this year, we’ve seen higher mildew pressure. I have quite a bit in the roses around my house and they are always a good indicator. Chardonnay is particularly sensitive, so we made sure to have our canopies opened up for air circulation by the 4th of July weekend. We pulled leaves early and the fruit looks clean. It’s funny, today when we talk of quality, we don’t even think about clean fruit. It has become the standard.

I mentioned earlier the actions growers can take. Our primary tool of control is water. On the technical side, we have great tools to aid us in irrigating. We measure leaf water potential (LWP) by seeing how much pressure it takes to push the water from a leaf out through its stalk, the petiole. This reading is much like taking someone’s blood pressure or measuring blood sugar. It’s a snapshot of water content in the plant.

We combine that information with a measure of soil moisture levels – the amount of water available to our vines. The neutron probe is a remarkable instrument that emits neutrons that lose energy when they impact hydrogen atoms in water. A neutron detector indicates weaker responses to neutrons as soil water content increases. We take these measurements weekly.

Recently, our leaf water pressure numbers were running higher than we’d like and they didn’t correlate with the soil moisture numbers or my visual observations of the vines. It just didn’t make sense to me. We had more than adequate moisture in the ground, and temperatures were moderate, yet we were getting LWP readings of 12 to 13 bars. We generally don’t want any higher than ten, and I had expected a reading of between seven and nine bars.

I’ve run into similar situations in the past. In 1999, for example, our sugar sample numbers just flatlined and that didn’t make sense. The numbers need to tell a story. They should not become the story. If the story doesn’t make sense, you have to be alert and apply your experience. While technology and numbers are marvelous tools, you can’t rely on them blindly.

What we discovered was that our LWP machine was reading two to three bars higher than it should have. We borrowed another one to compare readings, and the numbers of the two machines varied by two to three bars.  The readings of the borrowed machine were in line with the visual state of the vine and the soil moisture level.  We have had our machine recalibrated. Luckily, we didn’t over-irrigate (although I would prefer to put on too much water rather than too little because once the plants are stressed, it’s hard to get them back to functioning well again).

We are fortunate to be able to factor in leaf water potential and soil moisture levels with vine transpiration needs and the weather forecast to make our use of water as a tool more precise. But this little incident illustrates that, despite our technology, perhaps our best tool is referred to in the old adage of the grower’s footprints in the vineyard.

You overlay years of experience with the site and the clones and you increase your understanding of what works when and where. Experience is the ultimate tool.

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