What is frostbite?Garden frost is a concern for farmers that causes significant damage to crops every year. This phenomenon occurs at different times of the year and can completely destroy the crop and even damage the next year's crop. Frostbite occurs when a plant is exposed to temperatures lower than the temperature required for its growth, in which case the plant is damaged. Negative temperatures can disrupt the absorption of water by the plant's roots, which causes the plant to dry out and damage it.
What are the types of frostbite?
There are different types of frostbite and it can occur during the day or at night. The time of frostbite is also very important; it can occur at the beginning or end of the growing season. Types of frostbite include:
Frontal frostbite
When a cold air front passes over an area and its temperature is lower than or at the critical temperature for plants in that area, frontal frostbite occurs. This type of frostbite occurs during the day and night. And it is very difficult and almost impossible to deal with it.
Radiant frostbite
Radiation frostbite occurs due to radiation from the earth's surface in an area and occurs in clear, cloudless sky conditions. At night, the earth's temperature decreases rapidly and heat rises due to its lightness, and cold air, which is heavier, descends. The most damage from frostbite in Iran is related to this type of frostbite and it only occurs at night. Dealing with this type of frostbite is possible in some conditions.
Late spring frostbite
Orchard frostbite in spring causes more damage to trees than in early autumn. This frost damage often occurs in temperate regions and damages newly formed flowers and fruits. The duration of this cold is short-lived. Open flowers can withstand temperatures of minus three degrees and small fruits up to minus two degrees, but newly formed fruit is very sensitive to spring cold and can suffer up to 100% damage. Trees that require little cold and are in the fruiting stage will suffer a lot of damage if exposed to spring cold; therefore, it is better to use late-flowering varieties.
Winter Frost Damage
Winter frost damage occurs in winter when the temperature is minus ten degrees Celsius or lower. Sometimes the tree may freeze completely. Different species may have different sensitivities to winter frost damage. In evergreen trees, this type of frost damage can be damaging. If autumn frosts occur and the fruit has not yet been picked, the crop will be severely damaged and sometimes even completely destroyed. Winter damage can lead to the formation of ice crystals within the plant cells, causing damage to plant tissues.
What are the symptoms of frostbite?
Symptoms of frostbite include:
General growth retardation
No flowering
No seed germination
No nutrient uptake
Discoloration, water scorching and necrosis of leaves
In some cases, premature leaf fall and senescence
What are the methods of dealing with frostbite?
Methods of dealing with frost damage are divided into two categories: passive (long-term) protection methods and active (short-term) protection methods
a) Passive or long-term protection
Includes methods that are carried out before the arrival of frosty nights and include the following:
Choosing the right planting location
One of the most important things to prevent frost damage to plants is choosing the right location for a plant. Choosing the right planting location depends on factors such as the slope of the land, soil texture, shape of the land, wind direction, suitable location for air drainage, climate of the region and other things.
In cold weather, the upper part of the mountain cools down faster than the slope. Then the cold and heavy air flows to the valley floor; therefore, the valley floor becomes much colder than the mountain slope. As a result, gently sloping lands in areas where frost is possible are more suitable than deep lands and valley bottoms.
Suitable soil
Specifics such as soil texture, fertility, storage capacity, organic matter content, and soil color should be considered. The deeper the soil, the greater its ability to absorb heat. In areas where the soil is light and contains a lot of clay, the possibility of frostbite is greater, and for these types of light soils, it is recommended to irrigate before frostbite. When the soil has enough water, heat storage and transfer are better.
Choosing the right variety and rootstock
It is recommended to use late-flowering varieties that flower after the spring frost, and it is also better to use varieties that are more resistant to frost at the time of flowering.
In areas that are at risk of frostbite, grafting varieties onto resistant rootstocks is also considered one of the most effective measures for plant resistance.
Some rootstocks are more resistant to cold, for example, in the case of pistachio plants, in a comparison of the four important rootstocks of Badami Zarand, Sarakhs, Baneh and Atlantica, Baneh rootstock is the most resistant to cold and Atlantica rootstock is the most sensitive. Using resistant rootstocks at the time of grafting can be effective.
Fertilization and tillage
The use of fertilizers containing potash and animal manure can increase the plant's resistance to cold. After frost, fertilizers containing phosphorus can also be used to improve cold damage. In general, plants that have favorable conditions in terms of fertilization and irrigation have better resistance to cold and recover faster if exposed to cold. Also, plants that are exposed to water stress and do not have proper nutrition have little resistance to cold. Avoid plowing the soil in cold and icy conditions.