What to do with frost in grape sprouts?prevention and post-frost management tips
Miao Tianwen, etc
On January 6 and January 19, 2023, two low-temperature frosts below 0 °C occurred in Honghe, Yuxi, Wenshan, Chuxiong and other places in Yunnan Province, which had a serious impact on grape production in these areas. We investigated the occurrence of these two frosts, summarized the performance of frozen grapes, and put forward frost prevention recommendations based on the investigation and analysis and the existing experience.
1 Overall frost hazards
The existing grape area in Yunnan is about 40 620 hm 2, of which the main producing areas are Maitreya, Jianshui, Mengzi and Binchuan accounting for 2/3. The two frosts occurred at the time of bud break and flowering and fruit set, and a large area of grapes suffered frost damage, which seriously affected the yield and quality, and the yield was estimated to be reduced by about 45%. Taking Maitreya City as an example, there are fresh food varieties such as jasmine, summer black, sunshine rose, seedless white chicken heart, winemaking and table grape crystal, rose honey, wine grape cloud dance, and French Yi. The lowest temperature on January 6 was -2 °C, the lowest temperature in the region in 40 years. This was followed by a low temperature of 0 °C on 19 January, which exacerbated the damage. According to the survey, the area of Maitreya grapes was 6 736.7 hm 2, of which the frozen area was 4 347.2 hm 2. The purchase price of grape brewing raw materials in 2023 will increase by 1.5~2.5 yuan/kg over the same period of the previous year, and the purchase price of table grapes will increase by 3~4 yuan/kg compared with the same period of the previous year.
2 Information obtained from post-freeze surveys
1) The temperature varies greatly. From January 1 to 5, 2023, the temperature in Yunnan will be 9~20 °C, 18 °C during the day on January 6, drop to 6 °C at 8:00 p.m., 4 °C at 12:00 p.m., and -2 °C at 2:00 a.m. In the winter of 2022, the temperature in Yunnan was high, and the winter pruning of grapes was 15~20 days earlier than that in 2021. In 2023, the grapes were severely damaged by extremely low temperatures during the growth and development period.
2) Frost recurrence. Following the frost on January 6, the second frost occurred on January 19, and the grapes that did not germinate on the 6th suffered frost damage, and the germinated grapes suffered a second frost damage. The winter buds in the pom-pom stage were frozen to death, and the winter buds that did not enter the pom-pom stage were thin and yellow after budding, and the top of the new shoots died.
3) Extreme low temperature is more harmful to grapes during flowering and fruit setting. The flower spikes in the flowering and fruit-setting stages are frozen, and the light ones are brown as if they have been scalded by boiling water, and the heavy ones are dead; the fruit grains also turn yellow, the light ones are difficult to expand, and the heavy ones become dark brown, with the smell of sake lees, and fall off.
4) Inaccurate weather forecasts. The weather forecast on January 6 showed that the temperature was 6~18 °C throughout the day, but the temperature dropped to -2 °C at night.
5) Improper use of regulators. The use of regulators to prevent low-temperature frost mainly depends on its temperature sensitivity and activity under different temperature conditions. Some producers did not choose amine fresh ester (DA-
6), but brassinolide and sodium dinitrophenol were used. DA-6 can increase the enzyme activity at -3~15 °C, increase the content of auxin, cytokinin and gibberellin in grape plants, so as to improve photosynthetic efficiency and accelerate the metabolism of grape plants. Brassinolide can significantly improve plant metabolism at 15~25 °C. Sodium nitrate can promote the rapid flow of cell protoplasm at 25~30 °C or even higher. It can be seen that under low temperature conditions, the use of amine fresh ester (DA-6) is the most suitable. The use of brassinolide and sodium dinitrate could not improve the frost resistance of the tree when frost occurred.
After frost damage, only the branches and leaves of the damaged parts were cut off, and the damaged inflorescences and fruit ears were not repaired in time, and the damaged fruits were difficult to expand.
3 Factors influencing the degree of frost exposure of vineyards
According to the survey of vineyards in frozen areas, altitude, variety, tree potential, cultivation mode, growth period, management level and preventive measures are all factors affecting the degree of grape frosting, and different factors have great differences in the influence of grape germination, shoot growth, flowering and fruit set, yield and quality.
1) Geography. Due to the differences in altitude, the grape growing areas of Maitreya, Jianshui, Mengzi, Yuanmou and Huaning have obvious regional characteristics of climate. The survey showed that the Yuanmou grapes at an altitude of 1 050 m were less affected, followed by Jianshui and Mengzi at an altitude of 1 350 m, followed by Maitreya at an altitude of 1 420 m, and Huaning had the highest altitude (1 516 m) and the grapes were the most affected by freezing.
2) Variety. Compared with the grape varieties of Jasmine, Crystal, Rose Nectar, Summer Black and Sunshine Rose, the severity of frost exposure is as follows: Jasmine → Crystal → Rose Honey → Summer Black → Sunshine Rose.
3) Cultivation mode. On the whole, rain shelter cultivation is less exposed to frost than open field cultivation. In the open-field cultivation mode, the fruiting shoots from budding to young fruit stage are almost completely wiped out after the first frost, and even if there are a few remaining plants with flower spikes, the flower spikes are difficult to elongate, the fruit spikes are short, the pulp cells are damaged, and the fruit is difficult to enlarge, so it has no commercial value.
In the same area, the scaffolding has a light degree of frosting, and the erection has a heavy degree of freezing. The terrain is high, the ventilation is good, the tree is strong, and the germination is neat, and it is relatively light to frost. The branches are closed, the buds are not timely, the trees are weak, and the germination is uneven.
Under the greenhouse cultivation mode, the damage from budding to inflorescence separation period is heavy, and the new shoots and inflorescences close to the periphery and high terrain in the shed are seriously damaged, and the new shoots are yellowed, the leaves shrink, and the growth lag phenomenon appears, the ears and fruit grains are small, the peel is thick, and the yield and efficiency are low.
4) Growth period. Under the same low temperature conditions, the frost in the pompom stage, the growth period, and before flowering was heavier than that after fruit set.
5) Management level. The application of humic acid and other functional fertilizers, organic fertilizers, moderate nitrogen control, phosphorus and potassium fertilizers and medium and trace element fertilizers are balanced in the garden, the branches are fully lignified, and the frost damage is light.
6) Precautionary measures. Spraying plant growth regulators, watering, film mulching, and the use of heating lamps and heaters to prevent the harm in time according to weather changes are less harmful and vice versa. The effect of pre-freezing prevention is better than that of post-freezing remediation, and the above measures are basically ineffective after freezing. The preventive effects of different measures are detailed in Table 1.
Table 1 Investigation of the anti-freezing effect of jasmine in Maitreya vineyard using different preventive measures
4 Lessons learned
Combined with the investigation of the two frosts, the author summarizes the frost prevention treatment plans obtained from years of practice for the reference of producers.
1) Pay attention to weather changes. When the temperature is lower than biological 0 °C or before the onset of frost, spray 1.6% fresh amino ester (DA-6) with high activity at low temperature and 4 000 times + 0.01% 24-epibrassinolide (BR) 1 000 times + 500 times amino acids on grape shoots, leaves, inflorescences and fruit ears to improve the resistance of grapes to low temperature and induce grape plants to produce stress resistance genes. 1 more spray after the frost occurs to repair the frostbite cells. The author instructed Maitreya Hongxi to Hengjin, Mengzi Guohui and other jasmine vineyards (single film covered simple greenhouses) to use the above methods to prevent frost, two post-frost surveys, the freezing rate was only 2%, all appeared in the place without greenhouse film cover, frostbitten flower spikes and fruit grains (scalded with boiling water, brown), after cell repair to return to normal growth, single grain weight 8~9 g, mu yield 2.18 t, 16~20 yuan/kg. And the adjacent vineyards are out of production. This method is used on Anning, Mengzi, Jianshui Sunshine Rose, Summer Black, Crystal Grape, and citrus fruit trees have shown good anti-freezing effect.
Before repair
After the repair
Figure 1 Comparison before and after restoration of frozen inflorescences
2) December to January of the following year is the coldest and lowest temperature period in Yunnan, there may be a low temperature of 0 °C, during this period, it is necessary to cover the greenhouse film according to the convention, change the single film to a double film, increase the temperature in the shed with a heating lamp and a heater, keep the garden moist, increase the application of polyglutamic acid, seaweed, humic acid, microbial agents and other functional fertilizers, and maintain the fertilizer and water absorption capacity of the root system at low temperature. After the occurrence of frost injury, amino acid fertilizer should be supplemented in time to promote the normal growth of new shoots as soon as possible.
For vineyards that have not applied germination fertilizer before the frost, apply 1 time of high-nitrogen fast-acting fertilizer and an appropriate amount of humic acid or polyglutamic acid organic water-soluble fertilizer as soon as possible, the amount should not be large, but it should be timely.
Before frost, the body of the tree that has been applied with 30-10-10+TE high-nitrogen germination fertilizer should be sprayed with neutralized amino acids, algal and biostimulants, and preferably 1 humic acid fertilizer should be applied to the roots.
3) Before the frost comes, look at the weather watering, if the 2nd day is a sunny day, water boldly, if the 2nd day is a rainy day, do not water, the more watering the more serious the frost damage. After the occurrence of frost damage, it was quickly treated, spraying fresh amine ester and brassinolide, and applying high-nitrogen water-soluble fast-acting fertilizer of Sinochem Yangtian series, and lightly topping and tipping the damaged trees. The topping work was delayed for half a month, and there was a moderation process after the tree body was frozen, and the tree was relatively weak, and the lighter the topping, the better it was.
4) Strengthen management after frost to help grapes return to normal growth as soon as possible. In the early stage, the fertilizer and water management should be strengthened to ensure the supply of nitrogen fertilizer and water, and promote the growth of branches and leaves; in the later stage, more phosphorus and potassium fertilizers should be applied, and it is recommended to use foliar spraying or irrigation with Sinochem potassium dihydrogen phosphate, and the leaves and branches with insufficient maturity can be used with uniconazole + potassium dihydrogen phosphate to properly control the water supply, promote the maturity of branches, and improve cold resistance.