Late spring cold snap strikes: how to protect vegetables, wheat and fruit trees?

“Late spring cold snap” is a weather phenomenon in which temperatures in early spring are lower than the same period in normal years, and crops often suffer frost damage as a result. This kind of “dramatic turn” in the weather is very unfavorable to agricultural production. If preventive measures are not taken in time, crops can easily be frozen. So, what preventive measures are there against late spring cold snaps for vegetables, wheat and fruit trees?

I. Vegetables

In early spring, vegetable cultivation is mainly carried out in protected facilities, generally growing solanaceous crops, cucurbits, legumes, leafy greens and so on. Because the temperature drop is large and fast, vegetable seedlings find it hard to adapt, and the longer it lasts, the more severe the damage. A short-term cold wave damages the aboveground parts of vegetables, while a longer-lasting cold wave damages the underground parts, and in severe cases frost damage, flower and fruit drop, and even dead seedlings occur; at the same time, some infectious diseases also easily occur and spread. The prevention of late spring cold snap damage to vegetables is divided into 3 parts: first, damage to vegetables at the seedling stage; second, damage to vegetables at the adult plant stage; and finally, damage at the flowering and fruiting stage. For these three vegetables at different growth stages, we should have different preventive measures.

1. Damage at the seedling stage

(1) Symptoms of damage

Cotyledons damaged: the edges of the cotyledons lose their green color, but after the temperature recovers they can still grow normally.

True leaves damaged: the edges of the leaves turn dark green and then gradually dry up.

Growing point damaged: the terminal bud suffers frost damage, and at this point no new leaves will grow, greatly prolonging the plant's recovery period. If, as the weather gradually warms, the damaged plants still cannot recover, then replanting is needed.

(2) Countermeasures: cultivate strong seedlings. It is best to harden the seedlings at low temperatures, which can effectively improve the cold resistance of vegetable seedlings, and even if a late spring cold snap occurs, it can reduce the impact of cold on the seedlings to the greatest extent.

2. Damage at the adult plant stage

(1) Symptoms of damage: the edges often dry up, the plants become withered, and the relatively young and tender leaves lose their green color and turn yellow, and so on. Severe freezing causes the growing point to dry up, and the plant roots also stop growing new roots.

(2) Countermeasures: the first thing to ensure is not external conditions, but the plant itself. Only strong vegetable plants can reduce losses when hit by a late spring cold snap, because strong plants suffer much less damage. Therefore, cultivating strong plants is very important.

First, do a good job of hardening vegetable seedlings; second, let the vegetable root system grow strongly; third, there is the important issue of fertilizer and water. No matter what kind of plant it is, be sure to ensure its mid-growth nutrients, because fertilizing can support root development and also make the plants strong, so vegetables are generally given a topdressing.

3. Damage at the flowering and fruiting stage

(1) Symptoms of damage: when vegetables suddenly suffer a cold current or temperature drop during flowering and fruiting, the activity of the pollen of the flowering vegetables is reduced, which indirectly affects pollination, fertilization and so on, and also causes flower and fruit drop later. During the flowering period it also causes poor flower bud differentiation, which directly leads to deformed fruit. Severely damaged cucurbit vegetables also develop flower-topping.

(2) Countermeasures:

Vegetables that are in the flowering stage are relatively delicate. As long as they are damaged, flower and fruit drop easily occurs, and even the fruit that forms will be deformed. Therefore, the work to be done well in this period is prevention, so as to ensure the flowering and fruiting of vegetables.

First, pay timely attention to the local weather. Do not look only at these two days; be sure to look at several days, and preferably at the past half month as well, so as to better take preventive measures. When the temperature begins to change, do not water, so as to avoid frost damage. Prepare in time the items vegetables need to get through the cold.

Second, when the late spring cold snap comes, carry out insulation in time; vegetables can only do well if their temperature is stable. There are many measures that can be taken, such as setting up some wind barriers, and also covering vegetables with film. One thing the author particularly recommends here is rice straw, which can not only protect against the cold but also serve as fertilizer. In addition, smoke can be used for insulation, and irrigation, temporary heating and so on can all ensure temperature; before frost, intertillage can also be carried out to ease frost damage.

Vegetables have different growth periods, so when a late spring cold snap comes, the growth stages the vegetables are in differ. Treatment should be carried out according to the different growth stages, adopting the most effective measures.

II. Wheat

Generally, late spring cold snaps are most likely to occur after wheat jointing, and early-maturing varieties and varieties with relatively weak cold resistance should be the key targets for prevention.

1. For wheat fields lacking soil moisture, irrigate in advance before the cold wave arrives, improve soil moisture, regulate the microclimate near the ground, buffer the impact of cooling, and prevent frost damage. For wheat fields with good soil moisture that have not yet jointed and wheat fields with loose soil, carry out compaction to fill soil gaps, prevent air leakage and moisture loss, and at the same time control excessive growth.

2. 2—3 days after the cold wave, promptly investigate the freezing of young ears, apply fertilizer by category as a remedy, promote recovery growth, and strive for small tillers to catch up with large tillers and for large tillers to form more ears. For wheat fields where only the leaves are frozen or the young ear of the main stem has a freeze death rate within 10%, there is no need to fertilize; for wheat fields with a freeze death rate of 10%—30%, apply about 5 kg of urea per mu; for wheat fields with a freeze death rate of 30%—50%, apply 7—10 kg of urea per mu; for wheat fields with a freeze death rate above 50%, apply 12—15 kg of urea per mu. Jointing and booting fertilizer still needs to be applied normally.

III. Fruit trees

Late spring cold snaps cause the most obvious damage to fruit trees that bloom earlier, such as apricot, cherry, apple, pear and kiwifruit. On the basis of rational fertilization, irrigation, branch pruning and overwintering management, the following preventive measures should be taken:

(1) Measures to take before a late spring cold snap occurs

1. Strengthen soil, fertilizer and water management

It is recommended that fruit growers promptly apply a full-nutrition fertilizer to the trees. Fertilizer types: organic fertilizer, compound fertilizer and medium and trace element fertilizer, and irrigate promptly after fertilizing; irrigating the orchard and replenishing water and retaining warmth can alleviate the adverse effects of frost damage to the trees on the tree body, improve physiological functions, and enhance resistance and recovery ability.

2. For those about to bloom, it is time to irrigate. Especially when the forecast temperature is below zero. Before and after fruit trees bloom, pay attention to listening to the weather forecast, and before the cold current arrives, water to lower the ground temperature so that the flowering period is delayed by 2?3 days. These two days, fruit friends have asked me whether they can water. If the weather is dry, watering is needed; even if it is not dry, now that the late spring cold snap is coming, irrigation is also needed to improve the cold resistance of fruit trees, thereby avoiding the late spring cold snap.

3. Whitewash the trunk or spray limewater. Whitewashing the trunk can reduce frost damage to the trunk. In recent years, rot, gummosis and black water flowing on the trunks of apple, pear, peach, cherry and so on have often been caused by freezing, and whitewashing the trunk helps prevent severe low-temperature damage. 25?30 days before fruit trees bloom, spraying 1% limewater can delay flowering by 3?5 days, and a slight delay in the flowering period can avoid the damage. Of course, once your fruit trees enter the flowering period, you cannot spray.

4. Spray antifreeze agent

5. Covering and windproofing method. Use plastic sheeting, straw curtains, reed mats, straw mats and so on to cover fruit trees, retain the geothermal heat given off, and block the invasion of external cold air, thereby reducing frost damage. In the south, many sugar mandarins are enclosed with plastic, and the effect is good. This method is most suitable for use in young orchards or tree species with low trunks and short crowns; once the trees are large, it is not easy to do. Of course, it is recommended that when establishing an orchard, a windbreak forest should also be established, which can protect the trees from or reduce their exposure to severe weather such as late spring cold snaps and late frost, and reduce and alleviate the occurrence of frost damage to fruit trees.

(2) Remedial measures to take after a late spring cold snap occurs

1. Artificial supplementary pollination and good fruit thinning. For flowers that have not suffered frost damage and are opening, artificial supplementary pollination should be carried out in time. This requires collecting pollen in advance for later use. In some affected fruit areas, stop work such as flower thinning, and affected orchards should carry out careful fruit thinning after the young fruit has set, selecting and keeping normally developed fruit with a regular shape and relatively large size, and removing weak, deformed and frost-ring fruit; for some branches that have set fruit, an appropriate larger number should be kept.

2. Strengthen fertilizer and water management. Especially in low-lying plots with severe frost damage, promptly apply a quick-acting nitrogen fertilizer and water in time to promote the growth of fruit trees and keep the flowers and fruit that have not been frozen. Spray foliar fertilizer. Late spring cold snaps generally do not damage the leaves, so foliar fertilizer such as potassium dihydrogen phosphate should be sprayed in time, which can enhance the photosynthetic efficiency of leaves, produce nutrients, and ensure the normal growth of fruit trees.