Icicles in the Vineyard

Isn’t it ironic that the icicles above were caused by a method of frost protection? (Photo by John C. Pina)

One of the newer methods of frost protection involves the use of pulsating misters. This is how the water saving method works: well before the vines reach freezing temperature, the misters are activated coating the vegetation with water. As the temperature drops below freezing, the water starts turning to a “slushy” ice. As long as the misters keep putting out water, the surface of the ice keeps freezing, the ice gets thicker and in this case, longer. Unless the temperatures drop well into the 20’s, the continual buildup of ice keeps the vegetation at, or just below 32 degrees and prevents tissue damage. This type of frost protection is called Ice Encasement.

Wind Machines 101

In my last blog, I said I would explain how wind machines work to raise the temperatures in the vineyards, and also under what conditions, they don’t.

This will be the short course for those of you only interested in the basics. I’ll be taking bits & pieces from 2 websites that go into more depth than the average person needs or wants to know.

On this website:
http://biomet.ucdavis.edu/frostprotection/Principles%20of%20Frost%20Protection/FP005.html
Richard L. Snyder, Extension Biometeorologist University of California, Atmospheric Science, Davis, CA, had this to say:
More economic losses occur due to freeze damage in the United States than to any other weather related hazard.
…
TYPES OF FROST EVENTS
Advection Frost
An advection frost occurs when cold air blows into an area to replace warmer air that was present before the weather change. It is associated with moderate to strong winds, no temperature inversion, and low humidity. Often temperatures will drop below 32F (0F) and stay there all day. Advection frosts are difficult to protect against, but fortunately they are rare in California fruit growing regions.
Radiation Frost
Radiation frosts are common occurrences in California. They are characterized by clear skies, calm winds, and temperature inversions. Radiation frosts occur because of heat losses in the form of radiant energy. Under clear, nighttime skies, more heat is radiated away from an orchard than it receives, so the temperature drops. The temperature falls faster near the radiating surface causing a temperature inversion to form (temperature increases with height above the ground).
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I’ll limit this discussion to the two types of frost noted above; Advection & Radiation. These will be easiest to explain in pictures, provided by Iowa State University. Just pretend those trees in the graphics are really grape vines.
First, the Radiation Freeze:
The Radiation Freeze is a condition that can be mitigated by the use of wind machines. Since there is “warmer” air above the vineyard, the challenge is to bring that air down to the vineyard.
The use of wind machines can perform that function.

But in an Advection Freeze, there is no warmer air to bring down.
Operating a wind machine during an advection freeze can actually do more harm than good.

Well, that about sums up the short course. But if you enjoyed those graphics and want to see more that include the use of heaters, bonfires, smoke (of no value), tower-less wind machines, helicopters, sprinklers, etc., just click on the following:
http://viticulture.hort.iastate.edu/info/06iawgmtg/vineyardfrostprotection.pdf
So the next time the wind machines wake you up and somebody at the store or your work or gym mentions that “…it sure got cold last night”, you might be able to impress them by saying; “Yes, but luckily for the farmers, it was a radiation freeze and not an advection freeze”.

Harley Davidsons and Wind Machines

Question: What do Harley Davidson motorcycles & vineyard wind machines have in common?

Answer: They both have sub-standard mufflers for no apparent reason.
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My sister-in-law is originally from the Cupertino area. When my brother first brought her into the Napa Valley in the 60’s, she noticed the wind machines and asked what they were for. My brother told her they were just big fans that we turned on in the summertime to keep us cool. And she accepted that answer, however briefly. Now before you jump to conclusions about her intelligence, I’ll tell you that she is now the CFO of a major & prestigious winery in the valley. She may be a bit gullible at times, but she is no dummy!
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Last year we had a very cold Spring. That meant we had lots of nights that required frost protection for the vines. It had been years since I had served on this night patrol, but since we were a bit short staffed, I volunteered.

There is a network of communications around frost protection. The initial low temperature warnings can be delivered several ways. On some vineyards, there will be a vineyard foreman that lives at the vineyard and has a “hard-wired” thermometer alarm system that goes right into the bedroom. Some folks are linked into a multi-station weather tracking system on the computer. On some of our ranches, we have an automated system that calls whatever number is programmed, and in digi-speak conveys the current temperature, and other pertinent weather data.

Once the primary contact has been alerted, the frost protection “system” has been activated. While it varies from operation to operation, he/she may call someone else on the phone tree at that point, or he may just get dressed, head out and start the wind, sky and temperature monitoring process. If even a slight breeze comes up, it’s a good sign the temperature might not even get to freezing. Likewise for any type of a cloud cover that will inhibit the earths heat from radiating out into the atmosphere. But if it’s calm & clear, it’s time to start checking temperatures. Most vineyards will have one or more thermometers, and temperature indicating sensors. The thermometers are similar to the glass thermometers you may have at home, only bigger. The battery powered electronic sensors (that PVM uses) have a multi-colored light system indicating an approximate temperature range as follows: The nice thing about these sensors is that you can monitor the temperature from a distance, usually from a nearby road. We can monitor the rough temperatures for the Kapcsandy Vineyard from the Yountville Crossroad. We can monitor our Annapurna and Gemstone vineyards from the Silverado Trail, at least as long as the sensors indicate we’re still in the upper 30’s. At these temps, one person may be able to monitor several of the PVM managed vineyards in the Rutherford, Oakville and Yountville areas. When the temperature drops into the mid-30’s its time to start monitoring the thermometers for more accurate readings. So, more phone calls are made, to get more people out of bed and patrolling the vineyards. The traffic activity level increases as the temperatures drop. As the temp approaches freezing, the wind machines start coming on. One minute I can be walking the vineyards enjoying the quiet peacefulness and intensity of the stars. And the next minute, I’m pulling out the choke and cranking up the V-8 of a rather noisy Wind Machine. And even though it may be set to idle for a while, the quiet calm has been broken. And this is when Joe Local, or Joe Visitor, or maybe even Joe the Plumber first becomes aware that it is cold outside. It starts with this low-level buzz throughout the valley. Of course if you live within a quarter mile of a wind machine, you might argue that low-level buzz description. As the temperatures drop, the buzz can eventually turn into a symphony of internal combustion engines. The decibel rating for each varies as the wind machine rotates to cover a larger area. Some might even describe the sound as a prop plane, or planes circling. There was even a story years ago (perhaps bogus) about the out-of-town visitor that called 911 to report a plane in distress that had been circling for hours.
Keep in mind there are lots of different types of frost protection systems in use, including sprinklers, misters, smudge pots and electric wind machines. Those might be discussed in a future blog.
And there are completely automated wind machines. We monitor several of those on our vineyards, too. So, why monitor them if they are automated?
The following paragraph is taken directly the operator’s manual of one of the newer machines:
“The ____ is _____’s newest member of their automatic wind machine control family. It is designed for simplicity and reliability, but no automatically controlled wind machine should ever be used as a stand alone, unmonitored, defense against frost. Automatic controls were designed to assist the grower in starting and operating his machines only.”

We have found this to be true. One night, as the temperature was dropping, we noticed that one of the automated machines wasn’t coming on as early as it should. Turns out, when the propane tank had been filled, the tank valve was closed, and the propane delivery man forgot to re-open it. And another automated machine needs to be switched over to manual mode after starting. That’s because it will get false temperature readings from warmer air sent its direction from a neighboring wind machine that gets started after that first machine (AND shut itself off). Simply stated, there is too much invested to assume these automatic machines will start & function properly.

In my next blog, I intend to explain how wind machines work to raise the temperatures in the vineyards, and also under what conditions, they don’t.