How to prevent pears from freezing

Apple pear is the main cultivated variety in Hexi area of Gansu Province, which has become a famous fruit in the whole province and even the whole country because of its large fruit, juicy and sweet taste. However, the apple pear blooms earlier, and the flowering period sometimes meets the local late frost period. When it suffers from freezing injury, the yield decreases slightly, and when it is serious, it can't be harvested at all. Freezing injury has become the main disastrous climatic factor affecting the high quality and stable yield of apple and pear. Therefore, it has become an urgent problem to find out the cause of freezing injury and prevent frost at flowering stage.

First, the cause of frostbite

1. Climatic factors: Abnormal climate is the direct cause of freezing injury of apples and pears. After beginning of spring every year, the temperature rises gradually, the dormancy period of apples and pears is gradually lifted, and the cold resistance is rapidly weakened. During the flowering and fruiting period, apples and pears are particularly sensitive to low temperature, and their frost resistance is extremely weak. When -2℃ lasts for more than half an hour, frost appears.

2. Occurrence regularity of freezing injury: According to the observation of Zhangye weather station, the general regularity of frost occurrence is: the average occurrence date in Sichuan is between April 24 and May 26; Ruochuan area first appeared on April 1 day, and mountainous area first appeared on April 23rd. The latest date of occurrence is May 7th in Sichuan and June 9th in mountainous areas. The later the low temperature appears? The more serious the damage to fruit trees, the greater the loss.

3. Topographic factors. The investigation shows that at the same latitude, the higher the altitude, the heavier the freezing damage. Terrain has a great influence on freezing injury, and the leeward side is lighter, and the terrain where cold air is easy to deposit is more serious.

Second, the symptoms of frostbite

After the bud is frozen, its appearance turns brown or even black, the scales are loose, the bud shrinks, it can't germinate and then dries up. After the flowers that have already opened are frozen, the pistil is the least cold-resistant. First, freeze to death, the calyx bubbles, and the water in the ovary freezes and peels. After the young fruit is frozen, it shrinks and turns yellow, and the stalk falls off. Different parts of flower organs have different low temperature tolerance. Calyx has the strongest resistance to low temperature, followed by stamens and petals, and pistil is the weakest. The investigation shows that the order of cold tolerance from strong to weak at flowering stage of Pingguo pear is: budding stage >; Flowering period > young fruit period. The unopened flowers can tolerate the low temperature of -2℃ for half an hour, and the young fruits can only tolerate the low temperature of-1℃ for half an hour.

Three, cold and antifreeze technical measures

According to the occurrence and development law of freezing injury of apple-pear in flowering period, the effective flowers in mass production were summarized.

Anti-freezing measures at flowering stage:

1. Construction of orchard shelter forest. Shelterbelt can not only effectively prevent wind, but also improve ground temperature and prevent frost in early spring. Frost occurred in fruit trees in Zhangye city in spring, mainly due to advection cooling, and radiation cooling aggravated its harm. Therefore, it is effective to build windbreak forest in orchard by combining arbor with irrigation, and Populus tomentosa is suitable for arbor with high protection benefit; Shrubs should be planted under the shelter forest, preferably Elaeagnus angustifolia, and the stubble should be flat at 1. Forming a compact structure. Shelterbelt is set in the north-south direction. Especially in the areas with frequent frost damage in flowering period, the construction of orchard shelter forest should be synchronized with orchard construction as much as possible. According to the observation, when frost occurs, the temperature in the forest network can be increased by 65438 0℃, and the ground temperature is 3. 5℃ lower than outside the forest net. The closer to the forest belt, the lighter the damage.

2. Choose a suitable microclimate environment to build the garden. Choosing the right garden is the most effective anti-freezing measure for planting apples and pears. Practice has proved that frost in flowering period is closely related to many environmental factors such as land and topography, and the microclimate in orchard directly affects the severity of frost damage in flowering period. Apple orchards and pear orchards should choose the south or southeast slope with the lee facing the sun to reduce or avoid the direct invasion of cold air in winter.

3. Irrigation before flowering. Orchard irrigation not only increased soil water content, but also increased soil heat capacity and thermal conductivity. The temperature decreases during the day and increases at night, so the air near the ground will not be hot and cold, which has a strong control effect on the temperature change. Therefore, before the appearance of low temperature, orchard irrigation can prevent and slow down the harm of frost. According to observation, the night temperature of trees after irrigation can be 65438 0 ~ 2℃ higher than that without irrigation.

4. Enhance the tree potential. The same temperature and environment, because of different cultivation management, the strength of the tree is also different. The tree is strong and slightly frozen; This tree is not strong, and it has been severely frozen. Therefore, cultivating strong trees is also one of the measures to prevent freezing injury.

Fourth, emergency anti-frost measures

During the germination, flowering and young fruit period of apple and pear, we should pay attention to listening to the weather forecast and predict the time and intensity of frost. The following emergency measures should be taken before the frost comes.

1. Smoke and frost prevention. Smoking is currently the most widely used method. Mainly use firewood and chemicals to release a large number of smoke particles to form a smoke screen, and create a "small greenhouse" in the living space of fruit trees to prevent the ground from releasing heat. Smoke should be made of flammable materials that can produce a lot of smoke, such as wheat straw, weeds, fresh branches and so on.

When the temperature drops to 65438 0℃, the ignition time will continue to decrease. 200 1, Zhangye institute of flood and drought forests conducted fumigation and frost prevention experiments. The lowest temperature in the treated garden is 2 ~ 3℃ higher than that outside the garden. After the frost occurred, the frozen flower rate of the treatment garden was only about 1 1%, while that of the control garden was as high as 60% ~ 70%.

2. Covering method: Cover the tree tray with weeds, leaves, wheat sugar, manure, etc. , not only improves the ground temperature, but also increases soil nutrients and maintains water. According to the field test of Liuba Garden in Minle County, Zhangye, the ground temperature can be increased by 3 ~ 5℃, and the tree temperature can be increased by about 3℃, which can play the role of heat preservation and antifreeze.

3. Use chemicals to prevent freezing: Plant growth regulators are used to delay the germination and flowering of fruit trees. Spraying naphthalene and potassium hexanoate (250 ~ 500 mg/kg water) on the whole tree before germination can inhibit the germination of buds and delay the flowering period by 4 ~ 6 days. The antifreeze for fruit trees and flowers developed by Lanzhou University has been tried in Zhangye Garden. When sprayed one day before frost, the frost-free rate reaches 80% when the flowering period encounters low temperature of 2 ~ 3℃, effectively preventing the harm of low temperature to flowers and young fruits.