Frost protection – a hot issue for fruit growers

Facts: Antifreeze methods

Smoke: Smoke is created with, for example, fireplaces or torches in the plantations. A smoke layer is formed in the form of water vapor and prevents rapid cooling.

LPG: Used in mobile LPG cannons or so-called frost wagons. The LPG heats up in the corridors between the trees.

Fan: Used to remix the air when the temperature is lowest closest to the ground. Can only be used against so-called radiation frost, which is the most common during spring and early summer and which is a consequence of radiation of heat towards space. The fan method does not work during airborne frost, ie when cold air masses have entered.

Plant biostimulants: The trees are sprayed with a substance extracted from sugar beet. The substance helps the cells to maintain the right fluid balance, so that they do not freeze as easily. The method is new and has not been fully tested in Sweden.

Antifreeze irrigation: The flowers are sprayed with water that freezes to ice on the plants. During ice formation, heat is released, which means that it will not be minus degrees below the ice layer as long as water is added and new ice is formed. The method requires large investments and good access to water. Risk of damage to the trees if you do not have good drainage and the trees are left standing in water.

Source: Alex Benediktsson, advisor at the Swedish Board of Agriculture

– The frost damages the trees more because they have reached further in the development. In recent years, we have seen that there have been frost damage in southern Sweden. This is a growing problem, says Kimmo Rumpunen, researcher at the Swedish University of Agricultural Sciences in Alnarp.

A smoking machine became the solution for apple grower Rita Jarl in Villands Vånga northeast of Kristianstad.

It was not cheap, about 180,000 kronor, and to use it means sleepless nights when she has to drive non-stop back and forth between apple trees to get a warm, protective smoke mist in the cultivation.

Last year it was running three April nights from midnight until well into the morning.

– You get a little easily jet lagged afterwards, says Rita Jarl.

But she is motivated – if the buds are damaged by the frost, the harvest will be smaller and the quality worse.

The harvest will be both smaller and of poorer quality if the apple orchard is damaged by cold snaps early in the season. Stock Photography.

– I received relatively small damage compared to other growers in the area who had more frost damage to the apples.

Limited extent

Now we are also in a period of chilly nights, but on most plantations the trees have not come so far in the development of flower buds that they are damaged, according to Henrik Stridh, CEO of the growers’ association Äppelriket.

– In those who have had the coldest, there may have been injuries. But it is to a fairly limited extent so far, he says.

As long as the fruit trees are dormant, they are very cold-resistant, says Kimmo Rumpunen.

– But as soon as they start to show green tip, which many varieties have started to do now, the endurance decreases. It depends on how far the apple bud has started to develop.

He states that frost protection is a trend among Swedish growers. The inspiration is taken from other countries where various such methods have long been used.

In smoke machines of the type Rita Jarl, straw, hay or wood have been pressed into a cylinder and ignited. At the bottom there is a tank with water and fans that make the steam spray out sideways.

– It will be a smoke vapor with heat and water that is sprayed down to the ground, which will push away the cold, says Rita Jarl.

It becomes so smoky in the farm that she has to call the rescue service and warn, if she is to use the machine.

Air is pressed down

Another method is to use fans that push the air down to the ground. However, these only work if ground frost is the problem, ie if it is closest to the ground.

– The heat rises, so you blow the warmer air into the cultivation. The method comes from New Zealand and there are a couple of those that have been tested in Sweden as well. But it is only in certain, delimited areas, says Henrik Stridh.

Later in the late spring, if flowering apple trees are threatened by cold snaps, the trees can be watered with antifreeze. This creates ice caps around the flowers, which protect.

Large investments

But this presupposes that you have good access to water and extensive investments are required, as it is not possible to use the usual irrigation system for antifreeze irrigation, points out Alex Benediktsson, advisor at the Swedish Board of Agriculture.

In the longer term, adapting to a changing climate can also lead to growers switching to other apple varieties.

– We are considering what strategies we should have when it comes to developing the apple varieties of the future. They should not wake up too early, because then they will be more affected by the frost. So we try to think strategically to cope with these climate changes, says Kimmo Rumpunen.

Source: by

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