Symptoms of frost damage of wheat: the main stem of wheat plant and young ears of large tillers could still produce normal ears and bear fruit after being frozen. However, the number of grains per spike decreased significantly. When the frost damage was severe, the main stem, the ear of the large tiller and the heart leaf froze to death, but the rest could still grow. In wheat fields seriously damaged by frost, the leaves and tips of wheat are hard and brittle like hot water, and the stalks and young ears shrivel and die.
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The reasons of wheat frost damage are as follows: First, unfavorable meteorological conditions. If there is a sudden strong cooling weather and the temperature drop is large, winter wheat enters the wintering stage earlier than normal years without cold resistance exercise, and from the physiological point of view, it does not go through the accumulation of sugar and the process of cell dehydration, resulting in severe frostbite of wheat. If the weather does not rain continuously, the soil moisture is poor, coupled with high temperature and large evaporation, the dry soil layer of most wheat fields is 3-4cm thick, and the tillering section is in the dry soil layer for a long time. There is still no rain in March, and the worsening drought will accelerate the degree of frostbite in wheat. Second, the poor cold resistance of cultivated varieties in production is the internal cause of freezing damage. Third, improper cultivation and management. Sowing too deep or too shallow had a great effect on the cold resistance of wheat, and the normal sowing depth of wheat was 3-5cm. The dead seedling rate of plots with sowing depth less than 3cm was 22.9%, and that of plots with sowing depth greater than 6cm was 18.3%. Fourth, pour frozen water. Pouring frozen water is an important measure to prevent freezing and protect seedlings from overwintering safely. The death rate of wheat seedlings was 26.8% without freezing water, but only 7.3% after freezing water.
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Types of wheat frost damage:
(1) Winter frost damage
Winter frost damage is caused by the cold wave from the winter to the overwintering period of wheat. The extreme minimum temperature, duration and intensity of cold and warm sudden change determine the degree of damage. When the frost damage is mild, only the yellow and white leaves are dried out, which has little impact on the yield.
Winter frost damage of winter wheat can be divided into three categories: sudden drop of temperature in early winter, severe cold in winter and alternating freezing and thawing over winter.
1, early winter temperature drop type (November ~ December)
Refers to the wheat has just entered the winter period, suddenly the temperature drops below 01, wheat seedlings because of no cold exercise, leaves quickly withered. Wheat fields with weak seedling quality, poor soil preparation, large soil void and lack of moisture will be affected by frost damage, and wheat that is sown too early or grows too well because of high temperature in the early period is more vulnerable.
2, winter cold type (late December to early February next year)
It refers to the freezing damage that occurs when the ground temperature at the depth of 3 cm in the wheat field drops below -25T in winter. In winter, continuous low temperature and several strong cold currents will lead to severe withering and even death of wheat seedlings. The years with low accumulated temperature before winter, weak wheat seedling or dry soil in autumn and winter are more affected.
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3, alternating freezing and thawing (late December to the end of January the next year)
After wheat enters the normal overwintering period, the warming weather occurs, the temperature increases, the soil thaws, and the seedlings resume growth, but the cold resistance is weakened. After the warm period, if the temperature drops sharply, more serious freezing damage will occur. The external symptoms are severe leaf drying, first withered leaves, then dead tillers.
According to the symptoms of plants after freezing, the degree of frost damage in winter can be divided into two categories:
(1) The first category is severe frost damage. It occurs in wheat fields with jointing or about to jointing, and the young ears of main stem and large tillers are frozen, the growing point is opaque, atrophy and deformation, water loss and dry, which affects the yield. In a wheat plant, the main lotus and the large tiller entered the picking stage earlier than the small tiller, and were susceptible to frost damage. However, the development process of small tillers is slow and generally will not be frozen. After the main stem and large tillers are frozen, they can be promoted by fertilizer and water in time. Small tillers can be headed, but the ears are small and the grains are light.
(2) The second type is general frost damage, which occurs in wheat fields without jointing, and the symptoms are frozen leaves, dry yellow and white, but the main stem and tiller are not frozen to death. This kind of freezing damage has little or no effect on yield.
Frost damage occurred more frequently in late production, and the damage was heavy. Late frost damage is caused by sudden cooling caused by late frost, which causes low temperature damage to wheat. Especially in warm winter years, the spring varieties with early sowing and large sowing amount suffered heavily. There are three kinds of frost in production: advection frost, radiation frost and mixed frost. Advection frost refers to the invasion of cold air from the north, causing severe cooling. It is harmful to wheat in high terrain and wind slope. Radiation frost is produced on a clear, windless night when the ground radiation is strong and the near-surface temperature drops sharply. It is harmful to wheat in low-lying, river valleys and basins. Mixed frost is in the sky with dense clouds or dense fog or large water content, due to the surface heat loss reflection, reduce the ground heat loss, when the weather clears up, calm, the surface temperature suddenly drops at night, easy to form mixed frost. This kind of frost attacks a wide range, occurs more times, serious harm.
Causes and types of freezing damage of wheat in winter
2023 11/02