Frost damage in the vineyards and ways of prevention

Grapevine (Vitis vinifera L.), while known to be durable and resilient plants, can be sensitive to frost and low temperatures. Resistance to low temperatures is at its highest when the crop is dormant during winter, while most sensitivity is shown when new vegetation grows. 

However, different parts of the plant exhibit various stages of sensitivity to cold temperatures. The flowers are the least cold-resistant plant part and can get damaged at 0 °C; saplings and leaves suffer when the temperature drops below -2 °C and swollen buds at -3 °C to -4 °C. Dormant buds, canes, trunk, and roots are more resistant and are not at risk of damage until temperatures drop to -13 °C or -14 °C.

Nowadays, grapevine plants need to withstand and overcome unfavorable conditions, like frost, more and more often due to climate change. Frost is a coating or layer of ice that is formed when an outside surface cools past the dew point. The most common types of frost are: 

1. radiation frost, 
2. advection frost and 
3. rime 

From the winegrowing perspective, we have autumn, winter, or spring frosts.

Autumn frosts can accelerate the dormancy period, which could potentially weaken the vine.

Winter frost brings some benefits, such as eliminating (freezing) some pests and diseases while frozen water in the soil allows the necessary aeration. 

Spring frosts are the most significant problem for winegrowers. They occur after winter dormancy when vines enter the budburst stage and are more sensitive. Lately, we are seeing higher temperatures at the end of winter, causing an earlier start of the vegetative cycle and leaving vines more vulnerable to frost damage. 

The damage that frosts can cause can be severe. If primary buds are damaged, then a secondary, dormant bud will grow. However, the shoot that grows from dormant buds could not be fruitful, depending on the variety and conditions of the previous season. It is safe to say that by having primary buds damaged, we’re definitely losing yield. 

Frost Protection of the Vineyard – How to protect grapevines from frost

When it comes to frost protection, passive and active strategies are available. 

Passive solutions involve methods that do not require energy input into the system (windmills, heaters) and do not modify the vineyard climate. 

Where possible, protection should start as prevention. 

One of the first recommended measures is site selection (for planting the vineyard: if we have a choice, vines should not be planted in closed valleys with insufficient aeration or at high altitudes).

At the locations where frost is a common phenomenon (especially during Spring), the farmer is advised to choose resistant varieties and rootstocks or/and varieties that go into the budbreak phase later. For example, Chardonnay is known as an early bud break variety. According to studies, popular and internationally used varieties like Cabernet Sauvignon, Sauvignon Blanc, Syrah, and Tempranillo tend to enter the bud break stage at least seven days later than Chardonnay.

Furthermore, agrotechnical measures and the way we’re executing them can have a beneficial effect on frost and cold temperature resistance. By choosing to prune a bit later, we are making vines more resistant than the ones pruned earlier. In addition, pruning later leads to later bud break, which can be helpful in “escaping” frost. Opting for a taller training scheme is desirable in areas where we can expect late frosts. 

Active measures against frost

There are a number of ways to fight frost once we know it’s inevitable; some of the most common ways are heating, irrigation, and using wind. However, these methods come at certain financial costs, advantages, and challenges. It is important to know that depending on the type of frost, the location (and slope) of the vineyard, and the knowledge of the grower and the vines, different measures (or groups of measures) can be more suitable than others. Before choosing your frost protection, you are strongly advised to get support from a local licensed agronomist. 

Heating

• Candles are an effective but not really cheap solution that requires time and labor for setup and removal. Candles are placed in buckets filled with paraffin wax; once they are lit, they can burn for several hours and warm up the cold air closer to the surface. Lately, there are candles based on vegetable wax instead of paraffin wax due to environmental reasons.
• Wood heaters – small heaters are placed in quantities of about 250 per hectare. Like candles, they heat the air around the vines by burning wood pellets.
• Heating cables – cables are set up along the wiring system in the vineyard and, when needed, provide heating for the vine shoots 
• Smoke – By burning bales of hay, we create a smoke cloud that prevents heat from getting lost into the sky. If done correctly, the temperature is not going to drop way below 0 °C. It’s proven to be effective and relatively cheap. This measure should be applied only when the weather and surrounding environment allow us to do so.

Irrigation

This way of protection is based on the fact that during the transition of water from liquid to solid state, energy is released (80 calories). It’s most effective if we’re spraying when the temperature is 0,6 °C – 0 °C, and the spraying continues until the temperature climbs to 3 °C – 4 °C 

 is achieved. Continuous spraying causes the layer of ice to form on the surface, which causes the release of energy, subsequently keeping the temperature beneath the ice layer around 0 oC. Also, this way, we fog up the air, moisten the soil, and stop further cooling.  

Among the most important downsides of the method are possible system issues (pump or sprinkler malfunction) and the price since a lot of water must be applied to keep up with the freezing conditions so that ice is consistently wet. 

Wind machines

Wind machines, windmills, or helicopters are used to mix the lower, cooler layers of air and the warmer air above using strong propeller fans. This method is becoming the most used frost protection strategy. It is most effective in strong inversions with minimal to no wind. 

Covering the vines

Vines can also be covered with veils made of thermal protective fabric that protects them from frost and ensures the temperature around the vines is a few degrees higher. Possible downsides are the price and the application time. 

Sustainable maize production – 30

Repairing the damage

Depending on the level of frost damage to the crop, the farmer can take some corrective actions to decrease further damage and help the plants regenerate.

Grapevines have three buds: primary, secondary, and tertiary. Primary bud has the greatest crop (yield) potential but is also the most sensitive. The first thing we can do is wait for dormant buds to break, then we choose the ones that seem more robust (healthier) and are placed in desirable places on the vine; the rest are removed. Also, removing the buds is recommended if the vine has visibly damaged parts. 

In the coming season, more attention should be given to offering our stressed plants a stress-free environment with low competition and sufficient nutrients and water. The grower should perform proper weed management and take preventive measures to avoid pest infestation and disease (the damaged, exposed areas may serve as an entry point for many pathogenes) to give the best chance for vines to recover from the damages. It is important to be rational with the dosing of fertilizers, especially nitrogen-based ones, since excessive nitrogen fertilization can lead to the lush growth of saplings and less wood formation, which decreases vine resistance. 

Sources: 

1. Mirosevic, N., Karoglan-Kontic, J. (2008.), Vinogradarstvo
2. Hickey, C., Smith, E., Knox, P. (2018) Vineyard frost protection (Agricultural and Food Sciences)
3. https://wineanorak.com
4. https://www.aveine.paris
5. https://education.nationalgeographic.org