Grape blooming includes physiological blooming and non-physiological blooming. The former refers to the physiological drop of flowers and fruits caused by the internal reasons of the tree after the grape withers. The peak of flower drop is within 1 week after flowering, and then there are sporadic flower drops, which gradually tend to be stable. Like other fruit trees, falling flowers and fruits of grapes is a physiological disorder in the body. If it is heavy, the fruit setting rate is very low, and abnormal flower and fruit drop will cause a large area of yield reduction.
(2) Causes of falling flowers and fruits
The internal causes of grape flowering and fruit dropping mainly include unbalanced tree nutrition, incomplete flower development, too high nitrogen content, unreasonable pruning, boron deficiency, incomplete ovule development, incomplete flower development, poor pollination and fertilization, etc. External causes include low temperature, rainfall, insufficient sunshine, high temperature, drought, high nitrogen fertilizer, excessive growth, drug damage to stigma, infertility, bacterial infection and so on.
① Variety characteristics. The characteristics of flower bud formation, flowering and fruit setting of different varieties are obviously different. Kyoho grape has congenital ovule hypoplasia and high abnormal ovule rate. Its filaments turn backwards, which is not conducive to pollination; Grape fertilization takes a long time, and it takes about 120 hours to complete the whole pollination and fertilization process. If nutrition is insufficient, it is difficult to complete fertilization. Kyoho is a tetraploid variety, and its easy overgrowth affects the nutrient balance in the tree. Last year's excessive growth will make the branches develop incompletely and the quality of bud differentiation is poor, which will affect the fruit setting rate in that year. Excessive growth of new branches will increase gibberellin content and interfere with fertilization. At the same time, the vigorous growth of new shoots and the competition between flowers and fruits for nutrients will also affect fertilization, which will stop the development of fertilized embryos due to insufficient nutrients.
(2) The influence of unfavorable external climatic conditions. When the temperature drops below 0℃ before flowering, the reproductive organs will freeze to death. When the pollen mother cell divides, even if the temperature does not drop below 0℃, the ovule may be abnormal and the pollen vitality may decrease. When the flowering period encounters a low temperature below 10℃, it cannot be fertilized. At the same time, poor metabolic activity at low temperature and prolonged fertilization time also affect fruit setting. Insufficient light, leaves produce less light contract products, which is not conducive to fruit setting.
③ The management of fertilizer and water is unscientific. Too much nitrogen fertilizer and insufficient water in the germination stage can easily lead to excessive growth of new shoots, unbalanced nutrition and fruit drop. In addition, the lack of boron in the tree will affect the cell division of young tissues, making the ear brown before flowering and bent into shrimp-like shape, and the corolla is not easy to fall off. When boron is lacking, the pollen tube is slow in elongation and easy to break, which will affect fertilization and lead to falling flowers and fruits.
(4) unreasonable pruning. In order to control the excessive outward migration of the resulting parts, it is often the result that the mother branches are too heavy to be updated and pruned, which may stimulate the vigorous growth of new shoots, lose balance and lead to falling flowers and fruits.
⑤ Early defoliation. Early defoliation caused by excessive fruit, drought or serious diseases and insect pests in the previous year will lead to insufficient storage nutrition of trees, which will seriously affect the differentiation and development of flower organs, which is not conducive to flowering and fruit setting and is easy to cause flowering and fruit dropping.
⑥ Improper distribution of nutrients in trees. If the new shoots grow vigorously, excessive application of nitrogen fertilizer or heavy pruning will cause the new shoots to grow white, which will make the new shoots compete with the flower organs for nutrients, and the flower organs will develop poorly due to insufficient nutrients, resulting in falling flowers and fruits.
⑦ Planting is too dense. Too close-planted vineyards have poor ventilation and light transmission conditions, which affect pollination and cause falling flowers and fruits.
(8) Boron deficiency. The lack of boron in grape plants affects pollination, leading to flower drop and fruit drop.
Pet-name ruby pests. Diseases at flowering stage can lead to falling flowers and fruits. Gray mold is light, the floret is damaged and falls off, but heavy, the whole spike becomes brown and withered. Brown blight of ear axis mainly damages the young ear axis tissue of grape fruit. If not prevented in time, the ear shaft above the affected part will turn brown and dry. Diseases and insect pests in non-flowering period will affect the growth and development of grapes, affect photosynthesis and nutrient accumulation, cause nutritional imbalance, and lead to flowering and fruit drop.
Attending virus infection. In recent years, the spread of grape virus diseases, such as grape fan leaf virus, can form virus particles in transportation tissues to block sieve tubes, hinder nutrient transportation, and cause falling flowers and fruits.
(3) Prevention and control measures
① Select excellent varieties. Grapes will bear fruit sooner or later, which is related to varieties. Generally, European and American populations are easy to form flower buds, with high fruit setting rate, and easy to obtain early high yield, such as Kangtai, red banana, red honey and white banana.
② Cultivate strong seedlings. Strong seedlings not only have high survival rate, but also recover and grow quickly in the same year of planting, forming vigorous aboveground parts and roots.
③ Scientific fertilization. Choose a suitable place and soil to build a garden, open a big ditch in the garden, apply sufficient base fertilizer, improve the soil every year when you are young, apply fertilizer, and add a proper amount of calcium superphosphate or calcium magnesium phosphate fertilizer, and apply compound fertilizer many times during the growth period, so as to make the grape root system develop, promote the vigorous vegetative growth and reproductive growth of the upper part, form a large number of flower buds in the early stage, and carry out normal flowering and fruiting.
④ Apply less nitrogen fertilizer before flowering. 7 ~ 10 days before flowering, the new shoots that grow too vigorously are cored, and generally only the tender shoots of the unexpanded parts of the leaves are cut off by 3 ~ 5 cm.
⑤ Spraying boron at flowering stage. Boron can promote the germination and fertilization of pollen grains, increase the fruit setting rate, reduce the number of seedless small fruits, thus increasing the yield, and is conducive to the formation of aromatics and sugar. Alkaline soil is more prone to boron deficiency, so attention must be paid to boron supplementation. Spraying boron at flowering stage can supplement the demand of plants for boron, enhance the vitality of flowers and pollen, promote pollination and fertilization, improve fruit setting rate and reduce fruit drop. Generally, 0.3% borax solution 1 time is sprayed on Kyoho grape before flowering and in full bloom. The former is sprayed on leaves and inflorescences, while the latter is mainly inflorescences.
⑥ timely thinning flowers. Sparse the flowers before flowering, and remove the spike tip about 2 cm before flowering 1 week.
⑦ Reasonable close planting. Only by carrying out planned close planting and giving full play to group advantages, it is possible to make full use of land and light energy in the early stage, quickly occupy the shelf surface, improve coverage and leaf area index, and obtain high yield and bumper harvest.
(8) Strengthen field management and pest control. Prevent early defoliation, control the yield, and reapply the fertilizer of strengthening fruit and promoting bud at the early stage of fruit maturity, so that the branches are rich in nutrition, mature and fully differentiated, and the trees have sufficient nutrient reserves to meet the development needs of grapes from germination to flowering in the next year.
Pet-name ruby insist on ear bagging. On the premise of choosing a good paper bag, bagging should be done immediately after fruit setting is stable, heading and grain thinning are finished, and it must be completed before the rainy season to prevent early infection of diseases from causing grain loss.