Recently, I wrote an article about how earlier budbreak in grapevines increases the risk of frost damage. But do you know what methods exist to protect against this frost damage?
Traditional Method: Warming by Open Fires
The most traditional countermeasure is the use of open fires. The purpose is to warm the air by lighting fires throughout the vineyard while simultaneously creating upward air currents to mix the air layers. In the past, maintaining these fires was laborious, but nowadays solid fuels similar to those used for BBQ—capable of maintaining strong heat output over extended periods—have come into use.
Helicopter-Assisted Air Mixing
The second method involves the use of helicopters. By hovering helicopters above the vineyard, the air is mixed. However, while this approach offers immediate effectiveness, it is an extremely costly measure. Since temperatures typically drop to frost-damaging levels during nighttime hours, noise concerns also limit this method to certain areas where it can be deployed.
A Counterintuitive Approach: Frost Protection Through Irrigation
The third method is irrigation—a counterintuitive approach in a sense. The concept is to spray water in sub-zero temperatures, thereby encasing the buds and vine shoots in ice.
The critical point here is that spraying water does not "freeze" the buds, but rather "encases" them in ice. This actually protects the buds from sub-zero air temperatures. How is this possible? The principle is simple. Water freezes at 0°C and generally does not drop below that temperature. In other words, the interior of the ice remains at approximately 0°C.
At first glance, this may appear to be a low-cost, environmentally friendly method, but naturally, this technique also has several drawbacks. Things in this world are rarely that simple.
Questions About the Irrigation Method: Can Lensing Effect Cause Bud Damage?
Regarding this "state of buds surrounded by ice," I once read an article suggesting that the ice could act as a lens, potentially damaging the buds through light concentration. Since it was written by someone quite prominent, I cannot dismiss it outright as incorrect, but personally, I have doubts.
I have two reasons for this skepticism. First, I have never encountered such claims anywhere other than in that particular article. Second, there is the physical reality of "focal length."
I imagine everyone has, at some point in their lives, used a magnifying glass to concentrate sunlight and burn something. Think back to that experience. Did the object burn when you pressed the magnifying glass directly against it? And could you burn something behind the object while the magnifying glass was in direct contact with it?
As a matter of pure optical principles, concentrating light through a lens requires a focal length appropriate to that lens's curvature. Additionally, the refractive index plays a role. While it may not be impossible to achieve zero focal length with a single lens, it should be extremely difficult. This is especially true if the lens is formed by water, which has a refractive index of 1.33.
What I am suggesting is that it is physically impossible for ice—acting as a lens in direct contact with a bud—to damage that very bud through the concentration of sunlight. Therefore, I believe concerns about buds being damaged by this lensing effect of ice are unnecessary.
Emerging Technology: Introduction of Large-Scale Fans
Recently, in addition to the methods described above, the introduction of large fans—similar to those seen in Japanese tea plantations—has been observed. Japanese tea plantations can be considered pioneering examples in frost damage countermeasures. While challenges remain, this technology is gaining attention as a considerably practical and realistic measure.
How to address frost damage is not only a pressing issue in Germany but a troublesome problem worldwide.
