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1 Frost Protection Articles 1. Below is a link to a frost protection article written by John Marshall of Great River Vineyard and Nursery and first appeared in the MGGA's Notes from the North. Particularly pertinent is the info about using an airblast sprayer as a means to move air and apply water to the foliage/buds. This is a technique used more heavily in the strawberry industry where overhead irrigation throughout the field is used to spray water on the strawberry plants during a frost event. As was noted in Rebecca Harbut's recent document on frost protection, the freezing action creates enough BTU's of heat to stop the buds/blossoms from freezing. Frost protection, in the end, comes down to - there isn't a "one answer fits all" solution, but there are a number of options available that may best fit your situation or tolerance for the risk of a killing frost in your vineyard. Here's the article: 2. Here's an article on the risks and potential damage of frost on grapevines taken from University Virginia Viticulture Notes, March 26 - Tony Wolf Here's the link to the newsletter which you can sign up to receive via What are the risks of frost damage to grapevines? Aside from the obvious site considerations, the extent of bud/shoot development will affect the potential for frost development. Swollen, unopened buds can withstand temperatures into the low twenties. Even opened buds with a leaf or two exposed can occasionally withstand temperatures as low as 28 or 29F under some conditions. With some variance due to wind speed, cloud cover, and the relative dryness of the air, the temperatures (degrees F) that will damage grape buds and shoots are: dormant bud (<20F); dormant swollen (26F); burst bud (28F); one leaf unfolded (28-29F); and two or more leaves unfolded (29-32F). The forecast dewpoint temperatures for Tuesday morning are in the high teens, surprisingly low, meaning relatively dry air. This means that temperatures can dip quite low before condensation begins to form on tissues, and the drop in temperature will be fairly rapid. Those who are monitoring air temperatures in advance of flying helicopters or activating wind machines should be aware of the low forecast dewpoint temperatures, and will probably start active protection at actual temperatures of 35 to 37F, rather than waiting until 31 or 32F. Other than site selection, what frost control measures can be used? Most effective approaches are active energy inputs; heaters, helicopters and wind machines during air temperature inversions, and overhead sprinklers. With the possible exception of helicopters, unless you have this infrastructure in place, it won t help you in the next 24

2 hours. A detailed description of these and many other measures can be found in Chapter 11 of the NC Wine Grape Growers Guide ( But many of these systems are expensive and I want to know what I can spray to avoid frost now If only it were that simple and effective Products advertised to provide frost protection to sensitive plants fall into several categories: those that affect the freezing point of the tissue or the condensate on the tissue surface; those that reduce the population of ice-nucleating bacteria; those that retard the development of the plant (i.e., delay bud break); or perhaps reduce the point at which condensation of atmospheric moisture occurs on sensitive tissues. If you search the literature, you can find examples where all of these methods have been reported to confer some frost protection under some conditions some of the time. And you can find negative results. Publishing negative results from scientific inquiry is difficult, not because the results contravene accepted doctrine, but because journals are often more interested in advancing knowledge, not simply confirming existing knowledge. That said, yes, oils and other materials that inhibit tissue respiration have been shown to delay bud break to some extent mid-winter application was superior to a week-before anticipated bud break application. Concentration was critical to avoid killing buds. For these and other reasons, including cost of application, we have not actively pursued this course. Biocides such as copper (which in several forms is registered as a pesticide for use on grapevines), can reduce the population of ice-nucleating bacteria on plant surfaces. At least one commercial product was available (and might still be) that contained a cocktail of bacteria that were antagonists to the Pseudomonas syringae ice+ strain that normally populates tissue surfaces and is considered an ubiquitous biological ice nucleator. Under some conditions, application of these biocides or competitive bacterial strains has led to a small but significant depression in the freezing point of condensate on the tissues (this is unlikely to be a factor with the low dewpoints forecast for Tuesday morning though). Freezing point depressants (salts, sugars, polyols such as sorbitol) are another potential avenue and are of interest because certain cold-adapted (and heat-adapted) plants may show elevated levels of some of these materials in their cells, especially when stressed. But spraying the same compounds on the plant does not necessarily mean that the plants will absorb the materials or that they will confer the same freezing point depression in non-adapted plants. On the other hand, osmotically-active sugars and salts, the latter including some foliar fertilizers, could slightly depress the freezing point of condensate on the tissues. This assumes that the freezing of condensate ( dew ) on tissues quickly causes an ice nucleation (and freezing) of the subtending grape leaf/shoot tissue (a valid assumption with grapes). However, with dewpoints forecast in the high teens tomorrow morning, I would predict tissue injury (mid-twenties) before dew begins to form on the leaf surfaces (high teens). But as of now, the actual temperatures are not forecast to drop that low. I will be watching the forecast weather conditions though. I do understand the temptation to try any means of frost protection, no matter how faint the potential for success. The sprayable products do not have a very high success rate, but other than their cost of application, probably do not cause harm. If you choose to use

3 something, be sure it s a legal application (especially if using copper, which is a pesticide) and try to leave a row or two untreated as a check. From Viticulture Notes, March 26, 2012, Dr Tony K Wolf, Viticulture Extension Specialist, Virginia And here's the link to the referenced article by Tony Wolf posted on the Virginia Vineyards Association Website: from Phillipe Coquard & Bruce Reeve at Wollersheim Winery: Hi all, having 5 minutes to sit down at my desk,i wanted to share some of our experience here at Wollersheim Winery. Over the 40 years of growing grapes and my 28 years we have seen some degree of spring frost EVERY year but a couple. Every year we "can" and "expect" to lose 10 to 20 % of the buds due to spring frost. BUT we never have seen leaves, yes green leaves on Foch in March! Lots of good info has been circulating... The double pruning might or might not work but not on 10 acres or more...the risk associated having to go back and break brittle buds is greater than pruning once. Wind machines will work if one has one or some. Years ago.. Kocide was also sold as "frost guard", Tony makes reference to that. We have some on hand, will use it, have used it with success but you need to have a big enough foliar area, will not work on buds. One thing that has not been talked about.. It is not only the temp and how cold it will get BUT also the length of exposure to the buds. ONE of the easiest practices to do is to cut all brush, tree lines, any vegetation that could and will create a dam where the cold air will pool and sit. The longer it sits the stronger will the damage be! Cutting the brush will allow the cold air coming from the higher point to continue to flow and flow down to the lowest point.we have spent days and weeks to do so. Yes we have 3 stationary wind machines drawing the cold air and displacing it, we also have one of these "Frost Dragon" with gas fired ring and forced air, on the 3 point, behind a tractor, we travel through parcels that are far away from the wind machine. Bruce and I just finished to install these 3 machines in the rain. We have a weather station with probes at different heights, when it hits 35 at 2 feet off the ground we then start the protection. It will be a matter of how cold...between 27 and 31 I think that we have made a lot of difference in the past but between 25 and 26...I don't think that much will help...pray a lot and drink after either to celebrate or to cry... This week appears to be ok down here, next week might be challenging. Besides the crop loss...my concern is also the loss of pruning wood for the upcoming year.if it was to happen...my father with 60 years of experience advises us to "reprune",forcing lower and fruitful buds rather than secondary and tertiary buds not fruitful...will one have time to do so? He has done it when he was 18 he is 76..

4 Will miss the morning of the SVS as I will be coming back from Virginia from accepting our 6 Gold, Double Gold, Best of...champion Riesling, Best Blush because of the Foch...From East to West (winery of the Year), we are proudly putting Wisconsin on the wine world map! Will see you in the after noon to do the pruning demo (on leafed out vines...) Philippe and Bruce. 4. Was there any discussion of how far into the bud break stages the amigo/soybean oil can be used? Attached is an image of the BBCH scale ( for bud break stages. 5. Rebecca Harbut s article Understanding Frost and Frost Protection: Understanding Frost and Frost Protection Rebecca Harbut As the grape buds develop in the spring, the critical temperature the temperature at which buds and/or other plant tissue can be killed, increases as the bud stage advances. Therefore, the first step in frost protection is determining what bud stage you are at and decide what temperature is you critical point. Figure 1. Critical temperature (F) for grape buds. Slide courtesy of Dr. Paul Domoto, ISU Types of Frost: Radiation Frost. Frost typically occurs on a clear, calm night which allows the development of an inversion layer which is characterized by cold air that settles in the bed and becomes warmer until you reach the inversion layer where the temperature gradient is reversed and temperatures get progressively colder as you

5 Effect of Dewpoint During Frost Events Example 1: Air Temp = 35oF, Dewpoint Temp=33oF - Temperature will drop quickly until it reaches 33oF when condensation will form on the buds. - Heat of condensation will compensate for some radiative heat loss and slow the rate of cooling Example 2: Air Temperature =35oF, Dewpoint= 27oF - Temperature will drop quickly until it reaches 27oF - Damage to buds can occur quickly, so protective measures must be started earlier freeze conditions. increase in altitude. The inversion layer is typically around feet about the ground. Frost protection with wind turbines or forced air displacement systems are based on the idea of either pushing the warm air at the inversion layer down or forcing the cold air up. During a frost event, the plant tissue is warmer than the air, so the tissue radiates heat to the surrounding air and will progressively get colder and if air temperatures are colder than the critical temperature, the tissue will be killed. Advective Frost/Freeze. This type of frost/freeze occurs when a cold air mass moves through an area and is accompanied by strong wind. It is difficult to protect a crop under advective Importance of Dew Point. The rate at which the bud temperature drops will be relatively fast until the temperature reaches the dew point the temperature at which condensation of the water vapor in the air first occurs. The reason that bud cooling slows down when the dew point is reached is due to the release of heat that occurs when condensation is formed. This heat release compensates for some of the radiative heat loss slowing down the rate of cooling. So why is the dew point so important to watch? If the dew point is below your critical temperature, the buds will reach the critical temperature very quickly, and so protective measures must be accurately timed as damage can occur quickly. Under these conditions the white crystals typically seen during a frost may not form as there is no condensation at the freezing point, this is often referred to as a black frost. If the dew point is above the critical temperature, the buds will approach the critical temperature more slowly so you have some more time to make decisions. Calibrating Thermometers. Your ability to accurately protect against frost relies on accurate thermometers. It is therefore important to calibrate your thermometers. This is easily done by placing your thermometers in a container of ice water. The temperature should read 32 o F, if the thermometer is reading higher or lower, note the offset and write it directly on the thermometer so you can adjust the temperature reading in the field. Protecting Against Frost 1. Double/long cane pruning

6 Unpruned vines can be up to two weeks later to break bud compared to pruned vines. The buds will begin to open from the distal end, the basal buds will be delayed as they will not open until all the distal buds have opened. This can be an effective approach to minimizing crop loss due to frost however, there are some challenges. This double pruning approach requires a follow- up pruning which is labor intensive and therefore expensive. In addition, cane removal during the follow- up pruning can lead to extensive bud damage as the developed buds can break easily. 2. Irrigation Applying water to protect the crop from frost is used in fruit production and is perhaps the most effective method of crop protection, though it is expensive. The principle of protecting the crop through irrigation is based on the latent heat of fusion the heat released during the transformation of liquid water to ice. The transformation of one gallon of liquid water at 32 o F to ice at 32 o F releases 1200 BTU of heat. It is the release of this heat that maintains the plant tissue at 32 o F and prevents the tissue from freezing. Colder temperatures will require more water in order to provide enough heat to protect the crop. When to Start Irrigating. The general recommendation for fruit crops is to start the system when the temperature is 4 o F above the critical temperature. When the irrigation is turned on, the application of water on the plant tissue causes a short term dip in tissue temperature due to evaporative cooling (the same principle used to cool the crop during hot days). Therefore, it is critical to turn the irrigation on before you reach the critical temperature to ensure that the dip caused by evaporative cooling does not result in the tissue temperature going below the critical temperature. A wet bulb temperature can be a better indicator than the dry bulb (standard thermometer) temperature of when the irrigation should be turned on. 3. Wind Machines During radiation frost events (calm, clear nights) the air layers with the cold air near the ground forming what is called a temperature inversion. Wind machines and helicopters can be used to mix the air and bring the warm air down from the top of the inversion down to replace the cold air at crop level. There are several types of wind machines: tall fans that push the warm air down, air displacement systems that force the cold air up which results in the draw down of warm air. 4. Heat Heat can be added to the vineyard by driving around with a mounted heater like the Heat Dragon or multiple small fires around the vineyard. This can be an effective means to increase the temperature of the vineyard. The challenge with this approach is time and labor. If using a mounted heating device, you must be sure that you will have time to cover the area. If lighting fires, you must be sure to not light a big fire as it can cause a break in the inversion layer and draw in cold air. Therefore, it is a challenge to continuously monitor small fires.

7 5. Oils There has been some work showing that use of oils can delay bud break with winter and spring applications. Work done by Dami and Wolf ( accessed March 23, 2012) showed that soybean oil (i.e. Amigo) could delay budbreak (JMS stylet oil was more toxic) when applied in winter or early spring. It is doubtful that this would be useful if applied now when we are already in or very close to bud break.