Back to the vineyards! This week we are going to talk about frost and hail, two major topics especially for regions inside France these last several years.
Here are some exam questions that relate to this subject (forgive me for including the old ones, but I think there's often insight in them):
2016: When and how can hail cause damage at various stages of vine growth? What methods are most effective for preventing or responding to such damage?
2015: When and how does frost pose a risk to grape production? Evaluate the different methods of frost protection available to the grape grower.
1997: In the final weeks before and during harvest, a vintage may be spoilt by adverse weather conditions. To what extent can a producer adapt techniques in order to meet the problems that arise?
1994: What do vineyard owners, from various parts of the world, do about the effect of weather problems? Illustrate your answers with particular reference to heat and drought, rain and humidity, hail and frost.
1992: The 1991 vintage in Europe was affected by various climatic disasters. Discuss their impact on the vineyards and the wines produced.
One thing that I discovered when researching this topic for the Stage 1 exam was that there are two different types of frost that exert different pressures on viticulture. I think this is also an area where having some ready statistics at hand would be helpful, like what % of the Cote d'Or was damaged by hail in 2017?
It's also important to know, in the old world, which treatments are legal and which currently are not, as well as any recent changes there.
Excited to see your thoughts/outlines/examples!
Kelli, Sabrina Lueck, Sarah Bray
Hi Kelli and All,
Full disclosure - I am repeating Stage One this year, which I plan to use to my advantage, rather than beating myself up for not advancing to Stage Two. So obviously I can benefit a great deal from participating on this forum! But hopefully can offer something as well.
When studying the 2015 frost question last year, I recall getting bogged down for quite some time on the topic of winter freezing which, according to the examiner's report, is not what they want candidates to address. (When and how does frost pose a risk to grape production? Evaluate the different methods of frost protection available to the grape grower).
While the Examiner's Report comments point out that students spent too much time on winter freezing, it still seems to me that that that is relevant, because 1. They are sometimes referred to as frosts. 2. There are some interesting methods that viticulturalists are using to cope, such as covering up vines with geotextiles in Canada and preemptively planting hybrid grape varieties to better withstand cold.
I guess if I was answering this question, I would still want to address winter freezing in paragraph, before moving on to the main topic of spring and harvest frosts (also delineated in the examiner's report). How would the rest of you deal with it?
Anyhoo, I worked out a loose organizational scheme along the following lines. I provided more detail below when actually describing actual measures taken once the frost events occur.
GENERAL DEFINITION OF FROST eg frozen water that results when air temperature falls below freezing (32F/O C)
TWO MAIN TYPES OF FROST EVENTS
Advective = sudden very cold frosts blowing in - usually in winter, and from far away (maybe advective events aren't as relevant because vines would be dormant, but examiners want to see that we are aware of them).
Radiative (inversion) = Common type occurring in spring. Definitely need to say more here...
WHEN FROST MOST LIKELY TO OCCUR - CHRONOLOGY, LINKING TO GROWTH CYCLE
- (Here maybe is the place to briefly mention winter dormancy in very cold areas like Ningxia, Upstate New York, and Canada) then move on to the crux of the essay - spring and autumn events.
- In the springtime, after budburst - most damaging to plant and grapes: Numerous global examples of these (Burgundy, Argentina, recent Bordeaux, Piedmont, etc. etc.) Should point out that they are most dangerous March/April in Northern Hemisphere and September/October in Southern Hemisphere.
- Harvest frosts - I was not able to find out as much about these events or as many examples, so need to work on this portion. If any of you have insight, that would be great.
Methods of Frost Protection with Pros and Cons/Examples (Here, i think a list structure actually works but am curious about what others think)
Site Selection - Examiners report mentions its importance and how some candidates neglected to mention it. Knowing where to plant can be the best protection. Sites with cold area drainage, soils with good heat conductivity, planting close to large bodies of water etc.
High Wire Training eg Geneva Double Curtain. A pro - Frost hazard is reduced by up to 0.36 °C each 10 cm (3.94 in) above the soil level. - a con of this method would be that it necessitates wide spacing if mechanical harvesting is to take place, and it is costly.
Delaying Winter Pruning - in areas where frost is a hazard, growers may push back winter pruning as long as possible as a means of delaying bud burst and potentially reducing damage. Some also choose to leave more canes on the vines so that there will be extra if there is frost damage. Eg Rosemont in Ontario. The delay of pruning is useful for those early budding varieties like Pinot Noir and Chardonnay. In Champagne, Cordon de Royat pruning, a variation of spur pruning, is used in part as a means of combatting spring frost, especially for Pinot Noir grapes in the Cotes des Bar. Delayed pruning can be a disadvantage to larger vineyards because of time constraints and labor availability. A larger vineyard might need to begin pruning earlier in order to complete the job before budbreak.
WHEN NO PREEMPTIVE MEASURES IN PLACE OR WHEN THOSE FAIL
Heating the Vineyard with Burners or candles is one active technique used in many parts of the world to combat spring frost. Spring frosts proved damaging to vineyards in several areas of France including Burgundy, Champagne and Bordeaux, in April of 2017. Many healthy and developing shoots had benefitted from warmer weather earlier in the growing season and when temperatures fell as low as -7 deg C (19 deg F), many vineyards lost a lot of crop. Champagne for example especially suffered, losing as much as 25-50% of its crop in some areas. To cope, grape growers in the region relied on 5 liter paraffin candles called “bougies”, heaters and even helicopters to provide down drafts of warmer air. Such techniques have also been used in England. Ridgeview Wine Estates in East Sussex, which specializes in sparkling wines, also relies on bougies when frost is anticipated. The bougies create enough air movement to prevent frost pockets from forming. They also provide a protective layer of smoke that keeps heat from escaping. According to a spokesperson from Ridgeview, the vineyard team will stay up all night observing temperatures. As soon as frost seems imminent, they rush out to light the bougies, a process that takes about 50 minutes. This system has limited value in true freeze situations and can also release pollutants into the air. Burners or heaters require costly fuel and can also be polluting.
Fans/Windmills: Using various machines such as fans and wind machines to stir up warm and cold air, creating a protective inversion layer, are also useful ways to combat radiative spring frosts. If used in windless conditions above use can bring a 2-3 degree temperature increase around the fruiting zone. They do have a number of disadvantages. They are noisy, and in the presence of winds between 5 and 10 mph, relatively useless as the inversion layer won’t form. They are also expensive. Wind machines are typically installed every 6-8 hectares if fixed and every 4 hectares if portable. Heart and Hands Wine company in the Finger Lakes region of New York installs wind machines to cover every 4-6 hectares and estimates that the price per fan is approximately $50,000. Nevertheless, they are a common means of combatting frost. About 50% of vineyards in Ontario Canada use them and they are used in Napa and New Zealand as well. In England, Hambleton Vineyard uses a combination of burning pruning stems for fuel along with wind machines to deal with frost events. This tends to be much more efficient than using either one or the other and reduces the number of heaters required.
Helicopters work on the same principal as do fans and can supplement wind machines as they can actually adjust to the height of an inversion and move the air better in temperatures too cold for wind machines. They can also find and hover over specific frost pockets in vineyards and protect areas as large as 20 hectares in size. These are generally used only for emergencies though as they are very expensive and even dangerous, as the pilot needs to make very slow passes over the vineyard (2-5 seconds per meter). At Akitu winery in Central Otago New Zealand, subject to both spring and autumn frosts, the owner uses sprinklers as a first line of frost defense (see below) for his 30 acre vineyard, but helicopters if the situation is more severe. He describes the pilot as hovering just under the inversion layer and forcing the warm air to circulate back down to the ground. He eschews wind machines because he says that neighbors would find they disrupt the natural beauty of the area.
Overhead Winter Sprinklers: This is known as the aspersion technique. As the temperature drops, water is sprayed over the canes and shoots. As the water freezes around them, it releases latent heat which protects the vines. The ice that forms around the buds creates an igloo affect. As the temperature rises again, the water is turned off and the ice slowly melts.
Pros - Very effective.
Cons - Uses a very large amount of water – as much as 30 mm in one night, can waterlog soil, so preferable for vines planted on well-draining sites. If growers don’t have a natural water source nearby and rely on stored water, they must be sure to have enough to see them through the entire frost period.
A number of producers I spoke with in Bordeaux and in Spain, said that although there have been more frost events in recent years (April of 2017 notoriously damaging), they aren’t frequent enough to merit the expenses of installing frost- protection. At Pichon-Baron in Pauillac, it was pointed out to me that the expense, labor requirement, and time to lay out bougies on the property was 73 hectares which was simply too big. He said he would consider a helicopter in the future which indicates that there is an expectation that frost events might be more frequent, especially with early budbreaks from climate change. The obvious advantages are that this is the most inexpensive method.
This is super topical for me right now! The Walla Walla Valley and other areas of Washington state experienced a freeze last week. This kind of early harvest freeze happens about once every 10 years. This isn't a huge deal - early season frost can mean no crop, late season frost just means that there is no more ripening potential in the vine for the last little bit of the season.Many growers (Seven Hills in the Walla Walla Valley, Ciel du Cheval on Red Mountain) used wind machines. These can be a good tool if there is a temperature inversion (cooler air close to the ground and warmer air above). We don't have a wind machine in our vineyard and it wouldn't have worked anyways - we didn't have an inversion above our vineyard. Additionally, it can cost $300-1000 USD in propane or other fuel to run these machines. This kind of expense many not be economically feasible at certain grape price points.Here's a video that I shot today out in our vineyard. https://www.instagram.com/p/B3pkETKnCsJ/
Sabrina, your point about late-season frost is most helpful - eg. no more ripening potential because the freezing temp would cause the vines to shut down. But once the temperature warmed up again (if it does before picking), then could the vine potentially"bounce back" and ripen a bit more?
Sabrina you are a national treasure
Unfortunately not. When leaves freeze, they turn crispy and brown. The chlorophyll is busted and no more photosynthesis can happen. Which means no more sugar development even in warm conditions. I’m on a mobile and trying to post two photos from today. They’re the same row of Cabernet Sauvignon. I bet you can tell which one froze!
I shall tear up in this here forum.
Here's a link to a photo with unfrozen and frozen leaves.
Great - thanks!
Love the "do nothing" aspect. It's often an important acknowledgment! Liz sorry i missed you in LA last week...
I'm sorry I missed you too Martin!
I wish we could include crying as a legitimate first response to frost in the vineyard as at least two producers told me that that was how they coped with recent, devastating frost events. Of course they went on to explain that it's simply too labor intensive, and $$ to take any real measures of protection.
As a random aside - I'd love to know if you'll pick the frozen vines separately - I've heard that most of wagners wines are being frozen prior pressing to increase extraction. Also, while the photosynthesis will stop is there any potential for increased brix through water loss?
Sabrina, I have spoken with other producers using wind machines that only cost $50/hr to run and cover 5-7 acres. Is there that much variance in operating cost between different types of machines? This was a $25,000 machine so quite high end.
The Wagner's grapes are being frozen prior to fermentation? That's very interesting. Are you able to name your source?
Hi ladies, thank you for sharing. Elizabeth, very useful notes.
I have some quick comments:
- Champagne: A vineyard manager for a big company told me that the use of candles and burners has been prohibited in Champagne. He made reference to the Cahier de Charge, and I need to fact check it. He says people use site selection, training systems (cordon de royat), windmills and helicopters.
- Bordeaux: A winemaker disclosed that the main aim for the heaters is to create a dense layer of smoke to protect the vines from sunburn the next day. Usually when there's frost, there's blue skies the following day, so the sunlight would burn the leaves and green parts as they are covered with ice. The ice would work as a lense. Sabrina, what do you think about this?
- Helicopters: Petrus and DRC use it too, but in the case of Bordeaux they say it is a problem for the village, because of the noise during the night and early morning.