When will frost hit my crops? Frost can occur at different times of the year, autumn, winter or spring, and it is sometimes difficult to anticipate. This is why farmers need to keep an eye out for cold snaps on a regular basis. Winegrowers and arboriculturalists are the most affected, especially by spring frost. This frost can indeed endanger the buds that are already starting to develop their first green shoots. A critical cold snap in the spring could destroy a harvest.

To deal with these frosts, growers have access to two types of solutions :

• indirect (or passive) control, which consists of preventing frost damage. This involves actions taken before the arrival of the frost.
• direct (or active) control, which consists of implementing actions to deal with frost, when the risk is identified.

Indirect control solutions

Here are some examples of solutions that producers can implement before the arrival of frost in order to limit its impact as much as possible:

• The terrain: Sloping terrain is more conducive to the accumulation of cold. The cold air, which is heavier, will tend to stay at the bottom of the slopes. In the case of sloping land, it is therefore advisable to install hedges (and avoid deforestation) upstream of the vineyard to limit the arrival of cold air. On the other hand, hedges should not be planted downstream of the plot to avoid the accumulation of cold air.
• Working the soil: A compacted and weedy soil will tend to accentuate the frost. It is therefore necessary to control the work of the soil.
• Agronomic practices: In the case of vines, choose varieties that are more resistant to frost. To avoid spring frosts, give preference to late budding varieties (e.g. Carignan, Mourvèdre or Piquepoul). Pruning the vines later will facilitate this later budding. However, the choice of varieties is restricted according to the region, the PDO or other quality signs (for example, white Burgundy wine must be made from the following grape varieties: Chardonnay B, Pinot Blanc B and, as an accessory, Pinot Gris G).

Indirect control solutions are more economical than direct actions, but can sometimes be insufficient in the face of a critical cold spell.

Direct control solutions

Spraying

This technique consists of watering the crops with rotating jets. This allows a protective ice pack to form around the young leaves and buds. It is the solidification of the water that will generate heat and prevent the air trapped in the bag from falling below - 1 °C (freezing temperature of the bud). Crops can then be protected down to -6°C by spraying 1.5 mm to 2.5 mm of water per hour. The spraying must be continued until the temperatures return to positive.

Investment : 8,000 to 14,000 €/ha

Air mixing

Mixing can be done with fixed or mobile antifreeze towers, but also with a helicopter. The cold, heavier air remains at ground level. The aim is to stir the air in order to send the warm air to the ground. This makes it possible to even out the temperatures by mixing the warmer layer above and the colder layer on the ground. This device protects crops down to -4°C and generally allows for a gain of about 1°C.

Investment :

• on average 40 000 € to cover 5 ha for the anti-freeze towers
• about 200 €/ha/h for the helicopter

It [Sencrop] allows me to manage the activation of the towers at the last moment because there is a significant noise impact from the antifreeze towers and I try to limit the impact on the neighbours - Thibaut Henrion

In the case of land that accumulates cold air in lower areas, there are cold air extractors. This device allows the cold air to be sucked in and discharged several tens of metres above the ground.

Heating

It is used to heat the ambient air and can be done with candles, heaters, gas or oil burners. Along with spraying, heating is the most widespread technique in vineyards and has received a lot of media attention in recent years. This technique is very labour-intensive for lighting up at nightfall and for night watch. Burners and heaters can protect against temperatures down to -9°C and provide a heat gain of up to 5°C. Candles have a lower efficiency.

Investment :

• candles : 2,500 €/ha for 2 nights of control
• heaters : about 13 000 €/ha
• burners : 12 000 €/ha for 10 nights of control

Other solutions

Other direct control solutions exist, but are less widespread. Among these are :

• Covering crops : The INAO (Institut National de l'Origine et de la Qualité) does not authorise the covering of crops with anti-freeze tarpaulins. However, it is possible to cover the soil with straw or plastic. Beware, in case of advective frost, cold air accumulates under the tarpaulins and can therefore worsen the situation.
• The smoke veil : This consists of creating an opaque veil of smoke or fog during the night. This technique limits heat loss from the soil by radiation.
• Antifreeze bacteria in foliar spraying. This technique is still being researched.
• Dynamic heating : This device blows hot air and can be mobile or fixed. It is still a recent device and therefore not very developed.
• Heating cables : This device, marketed only in viticulture, consists of placing the rods and buds of the vine on heating cables to heat them.

How to set up a frost control system ?

To set up a frost control solution, it is first necessary to choose the most appropriate means of control for your needs and resources, but also to identify the best time to activate the system.

Choosing the frost control method

There are several criteria to consider when deciding which control method to use. Here are the main criteria :

• The type of frost : As not all frosts form in the same way, they are also fought in different ways. For example, stirring will not help against advective frost. Read more here about the difference between advective, radiative and evaporative frost.
• The surface area to be protected : for example, do not use candle heaters for very large surfaces
• The resources available : water, electricity, ...
• The available manpower : for example, do not use candle heating if little manpower is required for a large area
• The cost
• The topography of the land

Triggering your control system at the right time

In general, all frost control systems are expensive. It is therefore essential to trigger them at the right time to ensure their effectiveness. Sencrop has developed a number of features to help farmers better manage the risk of frost :

• Frost alerts to be alerted in real time when certain temperatures are reached.
• Frost forecasts to anticipate the risks over the next 4 days.
• Real-time monitoring of wet and dry temperatures on your map.

"If we have frost on the apples and we can't protect against frost because we don't trigger the intervention correctly in relation to the frost, we have lost everything" - Dennis Delannoy

Conclusion :

There are many ways of fighting frost, both passive and active. However, a bad identification of the risk of frost can compromise the harvest. To avoid being surprised by frost, weather solutions connected to your plots are now at your disposal and allow you to easily identify when to implement these control actions.

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