Late frost weather is very unfavorable to vegetable planting. How to deal with it?

Recently, frost weather has frequently appeared in major vegetable areas in China, which has brought great harm to vegetable cultivation in China. Traditionally, there is basically no frost after the solar terms in Grain Rain, but the weather is not beautiful, so it can be said that the frost is the biggest at this time? Natural disasters? How do we evaluate the losses after first frost? How to take measures to reduce losses? What management measures should we pay attention to after first frost? Become the most concerned topic for vegetable farmers. Therefore, combined with many years of plant protection experience, the author shared the harm of frost and some management measures after the occurrence, hoping to draw lessons from the vegetable cultivation management of vegetable farmers.

First, the characteristics of frost

The occurrence of frost is actually regular:

Low-lying: an old saying? Snow, mountains, frost, depression? In other words, the higher the snow falls, the more severe the frost is in the lower place. Drought and water shortage: when frost occurs, the drier the plot, the more serious the frost will be. Poor resistance: the weather is unpredictable in early spring. Whether cultivated in open field or greenhouse, the frost of vegetables with poor resistance is more severe, especially this year, cold and hot alternate frequently, and the resistance determines the severity of frost; The frost far from the village is heavier: the same frost is generally lighter in the suburbs than in the countryside, and lighter in the village than in the village. Generally speaking, because the solar term in Grain Rain has passed, the ground temperature has risen. So the current frost is characterized by freezing above but not below, and the roots below are intact. Frost lasts only a few hours, basically between 2 am and 5 am.

Second, the harm of frost to vegetables

The harm of frost to vegetables varies according to the cultivation environment.

Greenhouse cultivation: the recent frost has little or no effect on the greenhouse; Cold shed cultivation: the influence on cold shed mainly depends on the stress resistance of seedlings, which mainly has two aspects: one is to reduce the stress resistance of seedlings; The second effect is that there will be chilling injury, such as dehydration and wilting of leaves, but there will be no freezing injury; Open field cultivation: Frost is the most harmful to open field cultivation, basically freezing injury. Generally speaking, for fruits and vegetables, because the seedlings have just been planted, the plants have no resistance to stress and are most affected; Leafy vegetables are more resistant to low temperature, which will directly lead to the deterioration of stress resistance, but will not harm the root system. It is different from fruit trees to evaluate whether to preserve or abandon seedlings after freezing injury. So when to abandon the seedlings and when to protect them?

Abandon seedlings: If the following three characteristics are met, it is necessary to abandon seedlings decisively. First, the ground parts are frozen to death; The second is the fruiting period, for example, fruits and vegetables can be guaranteed before flowering and fruit setting, but in the fruiting period, they can't be guaranteed if they want to; Third, there is no preservation value. As long as the above three points are met, preparing the next crop as soon as possible is conducive to recovering losses. Seedling protection: At the seedling stage, some crops are frozen, but there are still core leaves, or although the leaves are frozen, the stems are still good. In this case, the root system is basically not damaged and can grow after seedling protection. As long as it is in the seedling stage, it should be protected as much as possible. Third, how to take countermeasures to alleviate freezing injury?

The main management goal after frost is to improve the resistance of vegetables. In terms of response measures, one mention two promotion three temperature control.

One support: aimed at the root system. Take certain measures to raise roots. If nothing is done, the root system at the lower part will be necrotic. The way to raise roots is to water them with small water and apply some fertilizers, such as organic water-soluble fertilizers containing natural biostimulants. It should be noted that watering must be done in a small amount, because the root system is the weakest at this time, and a large amount of watering is easy to cause root retching due to lack of oxygen. The second promotion: for stems and leaves. While doing a good job in raising roots, it is also necessary to promote the re-germination, branching and stress resistance of stems and leaves. Therefore, as long as there are stems and leaves, it must be promoted. Our vegetable farmers often spray the mixed solution of potassium dihydrogen phosphate and brassin to promote leaves, but this method is not recommended, because potassium dihydrogen phosphate is a good foliar fertilizer, but it takes a long time to be absorbed and utilized after entering leaves, which basically takes 3 days. The essence of brassin is hormone, which is too irritating. The more you use it, the faster the resistance will decline in the later stage. It is suggested to use plant-derived amino acids and plant-derived auxins, which can be absorbed and utilized fastest and take effect in 4~6 hours. Three controls: mainly for greenhouse cultivation. The daytime temperature in the shed is controlled at 24℃~26℃, and the medium and low temperature management is implemented. It has been frozen to death. If the temperature is suddenly too high, vegetables can't adapt at all. By raising roots and improving the stress resistance of vegetables, most of the symptoms of freezing injury can be alleviated. In addition, many vegetable farmers are eager to cut off dead leaves and black leaves after first frost, so they must let the seedlings slow down for two days before cutting off dead leaves, so that the plants can have a process of self-repair.

Fourthly, it is very important to prevent and control greenhouse cultivation diseases after frost.

1, cause of disease

The notable feature of frost is cooling, and there may be no freezing injury or cold injury, but the stress resistance of vegetables will definitely decline. Stress resistance is an adaptability of crops to unfavorable external environment. The stronger the pressure resistance, the wider the adaptability to the adverse external environment, and vice versa. After first frost, if the temperature rises sharply or the temperature and humidity in the shed are too high or too low due to improper management, it will easily lead to diseases.

Therefore, after frost, the prevention and control of diseases is very important for greenhouse vegetable cultivation. It stands to reason that after Grain Rain, gray mold, late blight, downy mildew and bacterial diseases will not be too serious, but many planting areas are still serious this year, and one of the main factors is the abnormal climate this year.

2. Effective countermeasures for diseases

In dealing with diseases, the overall principle to be grasped is that prevention is greater than treatment, and prevention and treatment should be combined.

(1), it is very important to improve the stress resistance of plants.

It can be said that improving the stress resistance of plants is fundamental to the prevention and control of pests and diseases. If the stress resistance of plants is high, the infection coefficient of diseases will be reduced. At present, the main measure to improve the stress resistance is to spray foliar fertilizers, such as the aforementioned plant-derived amino acids and plant-derived auxins.

(2) Environmental management

The environmental control of the shed is mainly aimed at temperature. Now all diseases, except powdery mildew and virus diseases, are almost related to the temperature, and they are stuffy. What should we pay attention to during the temperature control? Big ventilation? . At about 8 o'clock in the morning, the wind will open, and there will be a little breeze at first. With the increase of temperature, when the temperature in the shed reaches about 24℃, the whole tuyere should be opened. If you wait until the temperature in the shed has risen to 27℃~28℃ before opening the tuyere, you can't go down. Try to close the tuyere in the late afternoon.

In addition, if it is cultivated in a greenhouse, you can also open a small mouth at noon; If it is a cold shed, the bottom air outlet does not need to be opened.

(3) Disinfection in the shed

At present, powdery mildew, Fusarium wilt, leaf mold, late blight, downy mildew and other diseases are all airborne diseases, and cutting off the transmission source is better than spraying once. Therefore, it is more important to disinfect the shed with strong oxidant before sterilization. It is suggested that 42% trichloroisocyanuric acid wettable powder be mixed with water and sprayed all over the garden, and the tighter it is, the better.

In addition, no matter what stubble or vegetable, if you buy seedlings, you must bring them back. Don't plant it in the shed in a hurry, and spray it according to the incidence in previous years. Many vegetable farmers don't pay attention to this at all. Powdery mildew of melon, gray leaf spot of tomato, brown spot of eggplant and leaf blight of pepper are all caused by virus in seedlings to a great extent. Therefore, vegetable farmers must attach great importance to this.

(4), symptomatic treatment.

According to different incidence and disease classification, prevention and treatment are combined. Everyone can basically identify and diagnose the symptoms of the disease. I'm here to focus on the prevention and control plan for vegetable farmers' reference.

① Lower mycosis

At present, the lower fungal diseases mainly include downy mildew and late blight. It is suggested to choose pyraclostrobin+cymoxanil+Cyanidazole, which have a long-term accelerating effect and a good eradication effect on lower mycosis.

② Higher fungal diseases

For higher fungal diseases, we should first take preventive measures while increasing rheumatism. The recommended spray for prevention is difenoconazole+pyraclostrobin. If the disease has occurred, targeted drug treatment should be taken.

Botrytis cinerea and Sclerotinia sclerotiorum: the recommended drug is boscalid plus Bacillus subtilis; Powdery mildew: pyraclostrobin+hexaconazole; Anthracnose, target spot disease, gray leaf spot disease and stem blight: These diseases are the most difficult to treat in higher fungal diseases, so we can treat them by using combined drugs. The suggested drug is thiram+difenoconazole+thiophanate-methyl+prochloraz manganese salt, and the vegetable farmers have a good response with this combination. ③ bacterial diseases

At present, there are two main drugs for treating bacterial diseases, antibiotics and copper preparations. The main difference between them is that antibiotics are quick-acting while copper preparations are slow-acting. Therefore, vegetable farmers should choose drugs according to the actual condition.

In addition, viral diseases are the most difficult to treat, and there is no medicine to kill them at present. Therefore, the best solution is prevention. If it happens, the harm can only be reduced by passivation.

After vegetable planting encounters frost, it is first necessary to evaluate whether to protect seedlings together or continue to protect seedlings. If so, management measures should be taken around raising roots and improving plant stress resistance, and frost is often the high incidence period of diseases, so it should also attract the attention of vegetable farmers.