Excuse me, what are the first frost and the last frost?

Spring frost refers to spring frost, also known as late frost; Autumn frost is autumn frost, also known as early frost. According to different weather conditions, frost can be divided into advection frost, radiation frost and advection radiation frost. This kind of frost occurs when the temperature drops to the south. The wind is strong, the airflow is seriously disturbed, the upper and lower air are easy to mix, and the ground temperature is often higher than the temperature. Ground cream radiation cream refers to the frost formed at night when the temperature of ground and plant surface drops to 0℃ or below due to ground radiation and heat release, which usually occurs in sunny and windless nights with strong radiation. Radiation frost, that is, advection radiation frost whose surface temperature is lower than that near the surface, is also called "mixed frost", which is caused by the invasion of cold air in the north, resulting in a sudden drop in temperature and then radiation cooling at night to form frost. Most of the spring and autumn frost in China belongs to this type.

How to prevent spring frost (late frost)?

Spring frost (late frost) refers to the phenomenon that the temperature drops below 0℃ after heating up in spring. When the average temperature of a day drops to the lowest (critical temperature) for the growth and development of pear trees, some organs of pear trees will be frozen. The main organs of pear trees damaged by spring frost are buds, flowers and young fruits. Some foreign scholars believe that the dangerous temperature of freezing injury in germination stage is ~ 2.2℃ and that in flowering stage is ~ 65438 0.7℃. Some people think that the flower organs at -3 ~- 1℃ will be frostbitten to varying degrees. But whether it will be affected depends on the duration of low temperature. Generally, the low temperature duration is less than 4 hours. Although there is frostbite on the surface of plant organs, it can usually be recovered.

The main measures to prevent spring frost are as follows: first, choose varieties suitable for frost-resistant cultivation in the later period of this area. The second is to postpone the flowering period, so that the flowering period is after the late frost. Such as pear orchard irrigation or sprinkler irrigation, B9 spraying before flowering, trunk coloring, etc. Third, smoking. According to the weather forecast, on the eve of the first frost, several chimneys were erected in the orchard. When the canopy temperature drops to 65438 0℃, it will ignite smoke to cover the pear orchard, reduce the ground heat dissipation and increase the air temperature of the orchard. Fourth, the remedial measures after frost are: strengthening the management of soil, fertilizer and water to promote growth; Spraying boron, urea and gibberellin to flower organs can improve fruit setting rate.