Cold spring cold and late spring frost are two kinds: Low temperature cold injury mainly occurs in March to April, causing damage to spring vegetables such as rot, dead seedlings, falling flowers, and convulsions; late spring frost generally occurs in mid-April, so that the field The surface of the growing vegetable plant is frosted and damaged. In the late spring, the damage is generally heavy in the arch shed, followed by the greenhouse; the adult plants are heavier than the seedlings, and the flowering results are the heaviest. Most leafy vegetables are more tolerant to low temperatures and suffer less damage, while melons and solanaceous vegetables are less tolerant to cold, so they are affected a lot in the late spring.
The vegetable suddenly encounters low temperature at a higher temperature, and its physiological function is abnormal, such as various abnormal states such as leaves or fruits. Common symptoms in the shed are: dry leaves, yellowing, wilting, malformed flowers, falling flowers, early flowers or early tics.
The effects of the late spring on the different growth periods of vegetables and their countermeasures are summarized as follows for the farmers' reference.
Seedling damage
Most of the current greenhouse vegetables are in the slow seedling stage or the hair tree stage. If the cold current is encountered during this period, the above-ground leaves will suffer first. The cotyledon of the seedlings showed that the edge of the cotyledon was chlorotic, with "white borders" appearing. The temperature returned to normal did not affect the growth of the leaves. True leaf damage often manifests as dark green leaves on the edges and gradually dry. The damage at the growing point is more serious, often causing the top buds to catch cold and not to have new leaves. This will greatly delay the slow seedling period. If the severely damaged plants cannot recover after the weather is warming up, they must make up the seedlings separately. In particular, seedlings growing on the edge of the film are often subject to damage at the growing point.
Response measures: If it happens to be cold and it takes adverse effects on vegetables, take measures before it is done. The vegetable grower should turn passively to take the initiative to improve the seedlings' stress resistance early in sunny weather. Even if it is cold, the influence on the vegetable seedlings can be significantly reduced. Suggest:
First of all, seedlings need to cultivate strong seedlings. The ability of seedlings to grow strong and resist bad environment will be greatly improved. To nurture strong seedlings, the management of seedlings should pay attention to strengthening the light and controlling the seedbed temperature. In general, the temperature of most vegetable seedlings should be controlled at 25 to 30°C and 18 to 20°C at night. Pay attention to reduce the humidity, bed soil control can not be too wet. Also time seedlings are needed to prevent the formation of "tall-feet". Seedlings generally do not top-fat, with the matrix seedlings in order to supplement the seedlings nutrition, according to the seedlings for extra-root fertilizer. General spraying 0.2% potassium dihydrogen phosphate solution, such as seedlings pale leaf color, can be mixed with 0.2% urea solution sprayed, spraying 2 to 3 times can be seedling period.
Second, low-temperature hardening before planting. The purpose of hardening seedlings is to increase the adaptability and resistance of seedlings to the cultivation environment. The method is to gradually reduce the temperature of the seedbed 7 to 10 days before planting. The temperature is controlled between 18°C ​​and 20°C during the day and between 10°C and 12°C during the night. The short-term low temperature of 8°C～10°C can enhance the resistance of the seedlings and colonization. Easy to survive after. Increase ventilation as much as possible, and pay attention to shade at noon so that the seedlings are in a cool environment. Also pay attention to controlling the amount of water.
Adult stage victim
The occurrence of late spring and cold, greenhouse vegetables in the adult plant encountered cold hazards, often show that the edge of the leaves dry, wilting plants, young leaves chlorotic chlorosis and other symptoms. In severe cases, the growing point is dry and no new roots are found in the underground roots.
Response measures: Vegetables have robust plants, their resistance to nature is high, and they are also affected by cold weather. The degree of damage is also much lighter. Therefore, strong plants should be cultivated. The following points should be made:
The first is that seedlings are very important after the seedlings of the vegetable seedlings are slowly grown Due to the current high temperature of the greenhouse during sunny weather, combined with adequate water supply, the seedlings tend to grow in length, so temperature-control seedlings must be used to promote the growth of seedling roots. The key is to control the night temperature. If the temperature in the shed during the day is high, the night temperature is controlled at about 14°C. If there is rainy weather and the daytime temperature is not high, the night temperature should be controlled at about 16°C. When the weather is fine for several consecutive days, the minimum night temperature can be controlled at about 12°C to prevent leggings from growing.
The second is that it is important to cultivate a strong root system. Robust root system is the fundamental to improve the stress resistance of vegetables. After easing the seedlings, they need to work hard to promote the development of the root system. After irrigating the seedlings, the cultivator should try to cultivate early, and the first time it should be shallow ploughing to promote root extension. The second time requires a proper deep cultivator to promote the roots of the lower bar.
The third is scientific fertilization to promote strong trees. According to soil moisture combined with water fertilization. Can be used to promote the tree type attack fruit type Fang Run (20:10:30) 10 ~ 15 kg / mu for flushing, but also flushing Shilingke special formula fertilizer. This can not only meet the needs of vegetable growth, but also play a role in increasing the temperature of the ground to promote root growth.
Injury as a result of flowering
In the late spring, when the fruits in the fruiting period are suddenly exposed to low temperatures, the pollen activity at the time of flowering is affected, which affects pollination and fertilization, and often results in flowering and fruit drop. In flowering, sudden encounter with low temperatures often leads to poor flower bud differentiation, resulting in subsequent flowering or fruiting becoming malformed or malformed fruit. In the event of a relapse, the melons will even appear to have flowers topping.
Response measures: Due to the delicate flowering period of vegetables, most victims suffer from flowering, falling, or malformed flowers and fruit. Therefore, taking preventive measures as soon as possible is the key to protecting the fruit during late spring. Suggest:
First of all, we must pay attention to the weather forecast in a timely manner during the time when it is often cold, so that preventive measures can be taken early. And pay attention to before the variable temperature weather, it is best not to water in the greenhouse, to prevent the spread of various diseases caused by low temperature and high humidity.
Secondly, the need to increase insulation measures when encountering late spring, which requires multiple membrane coverage, therefore, do not remove early insulation film within the shed. In recent days, the weather has clearly improved and the temperature has risen rapidly. In an interview with the authors in Shouguang City and Qingzhou City, it was discovered that with the increase of temperature, many vegetable farmers had already removed the insulation film (two membranes, three membranes, etc.) in the shed early. The author reminded the vegetable farmers that because the end of late March to early April often occurs when the cold weather, when the outside temperature will drop to 3 °C or even -3 °C, the temperature inside the shed will also be reduced. Sudden cooling rate is too large, and often has an adverse effect on the growth of vegetables in greenhouses. It also needs to cover two membranes to increase the temperature inside the greenhouse. Therefore, the insulation film inside the shed cannot be removed temporarily. If the vegetable grower is afraid that the temperature of the shed is too high, the insulation film inside the shed can be placed on both sides of the shed, so that when the coldness occurs and the temperature inside the shed becomes low, these insulation films are fixed on the steel wire on the shed with clips. It's much better to leave early blindly.
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