Persistent Rain and Snow Arrive in Many Regions: How to Protect Vegetables, Fruit Trees and Wheat Against a Late Spring Cold Snap
According to information released by the National Meteorological Administration: average temperatures are expected to drop by 6-8°C in northwestern Heilongjiang, southeastern North China, southern Shaanxi, most of the Huang-Huai region, Jianghan, Jianghuai, most of Jiangnan, central and southern Guizhou, and central and northern South China; among these, local temperature drops in central Guangxi and southern Jiangxi may exceed 10°C; heavy snow or blizzards are expected in eastern and southern Qinghai, southern Gansu, southern Ningxia, the Qinling Mountains in Shaanxi, northwestern Hubei, eastern and southern Tibet, eastern Jilin and eastern Heilongjiang.
Here, the editor reminds our farmer friends that this spring's climate is changeable and prone to late spring cold snaps. Below are several measures for preventing and managing late spring cold snaps in vegetables, fruit trees and winter wheat.
1. Scientific Prevention and Management of Late Spring Cold Snaps in Early Spring Vegetables
Low-temperature chilling injury causes root rot, seedling death, flower and fruit drop, and premature bolting in spring vegetables; late spring frosts generally occur in mid-to-late April, causing frost to form on the surface of vegetable plants growing in the field and damaging them. Understanding the science of preventing and managing late spring cold snaps is especially important for vegetable growers.
[1] Low-temperature hardening of seedlings
After the seedlings have all emerged, the seedbed should be ventilated, and the amount of ventilation should be gradually increased as the weather warms, so as to subject the seedlings to low-temperature hardening, thereby improving their cold resistance and helping them adapt to the outdoor low-temperature environment.
[2] Adding protective facilities
Two methods can be used to add protective facilities: first, erecting windbreaks. Windbreaks block cold air and prevent further cooling of the ground surface. Second, planting in furrows and covering with plastic film. When transplanting early spring vegetables, the furrow-planting method can be used; the furrow should be deeper than the height of the vegetable seedlings, and then plastic film can be laid over the furrow.
[3] Temporary heating
In protected production, when a cold wave arrives, temporary heating can be carried out in seedling-raising sheds or production sheds by building simple coal stoves or installing electric lights, so as to raise the temperature inside the shed and prevent freezing injury.
[4] Irrigating with well water
After a relatively strong cold air mass has passed, when the weather is clear, there is no wind or only a slight breeze at night, and the temperature drops rapidly, especially when the ground surface temperature falls below 0°C and frost occurs, a large amount of well water can be poured onto the ground to greatly raise the ground temperature. This method can raise the ground surface temperature from 0°C to about 8°C, preventing frost from occurring.
[5] Lighting smudge fires
On frosty nights, producing smoke in the field can effectively reduce or avoid frost damage. But two points should be noted: first, the fire points should be somewhat dense so that the smoke screen can basically cover the entire orchard; second, the ignition time should be appropriate, and fires should be lit on the windward side from midnight to 2-3 o'clock in the morning and kept going until just before sunrise, with a smoke screen covering the ground; this gives the best effect.
[6] Timely intertillage
Carrying out intertillage before frost can reduce the severity of frost damage. Because spring temperatures gradually rise, once the soil in the beds is loosened by hoeing, it can better absorb and store solar heat; when frost damage occurs, the soil has already accumulated some heat, which can moderate the frost.
[7] Controlling pests and diseases
Low temperatures and high humidity easily trigger the occurrence and spread of gray mold and other diseases, so dead plants and fallen leaves should be cleared away in time and chemical control of pests and diseases should be strengthened.
2. How Fruit Trees Should Respond to Late Spring Cold Snaps
[1] Pay attention to weather changes and raise awareness of prevention
As far as possible, set up your own observations and records of air temperature and ground temperature in the orchard, and always pay attention to weather changes and weather forecasts. In particular, before fruit trees bud each year, on the basis of understanding the long-term weather forecast from the local meteorological department, always pay attention to short-term forecasts during the flowering period, so as to know in advance the timing and intensity of frost and take emergency preventive measures early.
[2] Create and choose a microclimate environment favorable to fruit tree growth
First, choose south- or southeast-facing slopes that are sheltered from the wind and face the sun, and avoid building orchards in low-lying land or closed valleys. Second, establish shelterbelts along the main wind direction of the orchard; shelterbelts can effectively block wind and can also raise ground temperature and prevent frost in early spring.
[3] Emergency frost prevention measures
Freezing injury prevention
① Irrigation for heat preservation: Around the flowering period of fruit trees, watch or listen to weather forecasts, and irrigate before a cold wave arrives to lower the ground temperature, which can delay flowering by 2 to 3 days.
② Smudge smoke to raise temperature: On the night when the cold wave arrives, light firewood and grass around the orchard to form smoke above the orchard, which can effectively avoid the harm of low temperatures during the cold wave.
③ Tree body protection: Use methods such as whitewashing branches and trunks with limewater, wrapping trunks with straw, mounding soil over the root crown, and covering the canopy with shade nets to prevent the fruit tree body from freezing, with particular attention to protecting young trees.
④ Bunching and bundling flowers and fruits: For fruit trees that have already set fruit in early spring, such as loquat trees, when “late spring cold snap” weather occurs, in addition to the above measures, young fruits should also be bagged for heat preservation to reduce the impact of freezing injury.
⑤ Facility antifreeze: Carefully inspect greenhouse facilities for greenhouse grapes, greenhouse pears, and delayed cultivation of citrus, promptly repair damaged frames and films, and reinforce and tie down the greenhouses to prevent freezing caused by damaged film or film blown open by wind. When the temperature inside the shed is too low, artificial heating should be used.
Post-freezing remedial measures
⑴ Moderate pruning: According to the different degrees of freezing injury suffered by fruit trees, prune timely and moderately. Pruning should be carried out after temperatures have steadily risen, generally from the end of February to late March; severely frozen trees should be pruned later rather than earlier. According to different degrees of freezing injury, flexibly determine the amount and targets of pruning.
⑵ Spraying foliar fertilizer: For frozen citrus trees, choose a clear, warm day from after 9 a.m. to before 3 p.m. and spray 0.3% urea plus 0.2% monopotassium phosphate, or a highly efficient compound foliar fertilizer, once every 5 days for 3 consecutive sprays, to supplement nutrients.
⑶ Pest and disease control: After freezing, the tree body is prone to pests and diseases, so dead branches and freeze-injured branches should be removed in time and pests and diseases controlled to keep the tree body healthy and vigorous.
[4] Innovate cultivation models
With the frequency of late frost damage, for tree species with relatively high output value and suitability for protected cultivation, such as large cherries, peaches, plums, apricots, and grapes, the scale of protected cultivation should be increased, thereby effectively avoiding the harm of late frost while increasing output value. In addition, new technologies such as growing grass, mulching with grass, and sprinkler irrigation in orchards also have relatively notable effects in reducing late frost damage.
3. How Winter Wheat Should Be Protected Against Late Spring Cold Snaps
In the spring-type winter wheat areas of Hubei, Anhui and other places in the middle and lower reaches of the Yangtze River, sowing is relatively early, and excessively vigorous wheat appears; late spring cold snaps easily freeze some young spikes. In the northern Huang-Huai-Hai and northwestern wheat regions, as well as central Shanxi and northern Shandong, where sowing dates are relatively late and seedling conditions are relatively weak, wheat has poorer cold resistance and is also prone to freezing injury. In freeze-injured wheat, the leaves look as if they have been soaked in boiling water, and the main stem is frozen to death, but the tillers are still alive.
[1] Pre-disaster preventive measures
1] Classified management: Combine the characteristics of seedling conditions and weather changes to provide classified guidance for wheat fields, strengthen field management, and improve the cold resistance of plants. For wheat fields with excessive growth, “control” should be the main approach, adopting measures such as compaction, deep hoeing, and spraying plant growth regulators to inhibit overly rapid growth and development of wheat, avoid premature jointing, improve cold resistance, and at the same time improve lodging resistance. For vigorously growing wheat fields, the first fertilization and irrigation in spring can be postponed to the late standing stage or around jointing.
For ordinary wheat fields, “combining promotion and control” should be adopted, first compacting and then shallow intertillage, so as to raise temperature and preserve soil moisture. At the standing stage, apply an appropriate amount of topdressing and irrigation to promote tiller growth and strive for more spikes. For weak seedling fields, “promotion” should be the main approach, doing as much early hoeing as possible to raise ground temperature, increase tillers and develop roots; note that hoeing should be shallow to avoid damaging roots. After greening, apply quick-acting nitrogen fertilizer according to soil moisture conditions; for weak seedling fields, as long as soil moisture is still acceptable, early spring irrigation should be avoided so as not to lower ground temperature. Generally, topdressing and irrigation are carried out in the late greening stage or early standing stage.
2] Irrigation before freezing: Irrigation before freezing is one of the most effective measures to defend against late spring cold snaps. Before a strong late spring cold snap arrives, wheat fields at risk of freezing injury must be irrigated in time; regulating the microclimate near the ground surface can significantly reduce freezing injury.
3] Apply more organic fertilizer: During the standing and jointing stages of wheat, apply more organic fertilizer as well as phosphate fertilizer and potassium fertilizer to promote root development, inhibit excessive aboveground growth of wheat seedlings, and enhance cold resistance.
4] Spray regulators: Before a late spring cold snap arrives, spray plant nutrients on the leaves to improve plant immunity and the ability to withstand various disasters and reduce damage.
[2] Post-disaster remedial measures
1) Supplementary fertilizer and irrigation: Wheat is a crop with tillering characteristics. Wheat fields that suffer early spring freezing injury will not have all tillers frozen to death; small tiller buds can still grow into tillers and form spikes. As long as management is strengthened, a good harvest can still be obtained. Wheat that has suffered early spring freezing injury should immediately be given quick-acting nitrogen fertilizer and irrigation; the synergistic effect of nitrogen and water will promote early tillering of wheat, help small tillers catch up with large tillers, increase the rate of tillers forming spikes, and increase the number of spikes per mu, thereby reducing the loss from freezing injury. Generally, apply about 10 kg of urea per mu as topdressing.
2) Intertillage to preserve soil moisture: Raise ground temperature, increase the number of tillers, and obtain a good harvest.
3) Spray foliar fertilizer: After wheat is frozen, promptly spray a plant cell membrane stabilizer on the leaves, which has a clear promoting effect on the recovery of wheat growth, shown as rapid growth of medium and small tillers and rapid development of dormant buds.
4) Do a good job in pest and disease control: Freeze-injured wheat fields are more vulnerable to pests and diseases and should be controlled in time. To control wheat sharp eyespot, powdery mildew and rust, triadimefon or carbendazim can be sprayed. For aphids, imidacloprid can be sprayed for control to reduce losses.