1. Growth and fruiting habits Citrus is a small subtropical evergreen tree. Root system often lacks root hair in general soil environment and relies on mycorrhiza to absorb water and mineral elements. There are three growth peaks every year, which are staggered with the growth of branches. Due to the influence of varieties, rootstocks and soil conditions, the root distribution is significantly different.
Citrus trees are short, with erect or open crowns. Strong branching, poor top advantage, balanced stress between branches, and often no obvious central trunk. Most crowns are round or semi-circular. Branches without thorns or short thorns often grow many times a year. Generally, there are three shoots in northern orange areas, which are divided into spring shoots, summer shoots and autumn shoots according to the occurrence period. Spring shoots grow slowly in northern orange area, with rich tissues and thick and round branches. June-July is the germination period of summer buds, which is irregular and grows rapidly. The branches are thick and long, and the organization is not full. Autumn shoots germinate from August to September, mainly at the top of spring shoots and summer shoots, and the early autumn shoots that germinated in the early stage can also become good fruiting mother branches. The late autumn shoots after September are often unable to mature normally in the northern marginal nuclear area, and are vulnerable to freezing damage, which reduces the overwintering of the whole tree and needs to be controlled. After the new branch stops elongation, the tip falls off by itself (the terminal bud "shears itself".
In addition to 1 main bud, there are more than L ~ 3 auxiliary buds in the axils of citrus leaves, which often germinate at the same time or later than the main bud, making citrus branches densely clustered.
The flower buds of citrus are mixed buds, which can be formed by several books at the tips of various robust shoots. If the new bud grows many times, the place where the flower bud occurs will move up. When flowering in spring, the fruiting branches extracted from mixed buds are generally very short. There are two kinds of fruit branches: leafy fruit branches and leafless fruit branches Young trees and trees with strong tree potential can mostly produce leafy fruit branches with high fruit setting rate. In the second year after fruiting, vegetative branches or fruiting mother branches can be produced. Time-free fruit branch is a kind of degraded fruit branch, which mostly occurs in old fruit trees and trees with summer branches and autumn branches as the main fruit branches. This kind of fruit hanging technology is dead after hanging fruit.
Citrus flowers are mostly solitary or clustered, which are complete flowers and can pollinate themselves and bear fruit. The stamens of mandarin oranges often degenerate and the anthers lack pollen; The pistils and stamens of Nanfeng tangerine also degenerate, and both of them can parthenocarpy and bear seedless fruit.
2. Environmental requirements: Citrus likes warm weather, and the annual average temperature is required to be above 15℃ ~ 16℃, the monthly average minimum temperature is above 5℃, and the absolute low temperature in winter is not lower than 1.5℃. In the northern orange area, the main factors limiting the expansion of citrus planting are the low temperature in winter (generally up to -7 degrees-10 degrees), the period and duration of low temperature.
The growth period of citrus requires humid climatic conditions, and the annual precipitation is1000 mm ~1500 mm. Drought in summer and autumn often leads to leaf curl and defoliation, which affects fruit development and even causes fruit drop. Fruits developed under drought conditions have rough skin, thick capsule wall, less juice and poor flavor. However, too much rainfall can easily affect pollination, reduce light intensity and aggravate physiological fruit drop. The ideal air humidity for citrus growth is about 75% relative humidity.
Citrus is more shade-tolerant than deciduous fruit trees, and more scattered light can meet the needs of growth. But there are differences between varieties. Compared with ordinary citrus varieties, satsuma oranges prefer light. When the light is insufficient, they often bear fruit outside the canopy. The fruit needs sufficient light in the ripening stage, which can make the color bright, the sugar content high and the flavor rich.
Citrus has wide adaptability to soil, and the suitable pH range is pH 5.5 ~ pH 7.5. The rhizome of Fructus Aurantii is acid-resistant, and the rhizome of Fructus Aurantii Immaturus (a kind of lime) is slightly alkaline. The soil with high organic matter content and strong water and fertilizer conservation ability is the most suitable.
Seedling cultivation and gardening
1. Citrus seedlings have small reproductive variation, strong tree vigor, good cold resistance and long economic life. Therefore, in the past, the cultivation of citrus seedlings was mostly carried out in northern orange areas, forming some local varieties with strong resistance. However, the seedlings began to bear fruit late, and it often took 8 ~ 10 years to put into production after planting. However, mandarin oranges, which are now popularized in production, have strong cold resistance, so grafting is adopted when a large number of seedlings are propagated.
Rootstock is mostly orange (also known as orange, commonly known as smelly orange), which has the advantages of good compatibility, short tree, early fruiting and so on, especially in the northern orange area, and also has the characteristics of strong cold resistance. When bitter orange is not tolerant to saline-alkali and the soil salt content is too high, it is easy to appear iron-deficient yellow leaves. Therefore, citron orange with strong salt tolerance should be selected in coastal beach areas. When planting citrus in mountainous areas, you can also choose orange, orange or crab orange with deep root distribution and strong drought resistance as rootstocks. When selecting scion varieties in northern orange area, we should choose early and middle maturity varieties with strong cold resistance. Early fruit harvesting is beneficial to the recovery of tree vigor and the improvement of cold resistance of trees. Mid-late-maturing or late-maturing varieties (lines) often cannot mature normally before cooling in autumn and winter, so it is not suitable for selection.
The common methods of grafting and seedling raising of citrus include single bud abdominal grafting, single bud cutting and half-T bud grafting. Cutting and budding techniques are basically the same as those of ordinary fruit trees. The suitable period of bud grafting is August-September. Citrus has thin branches and thin cortex, and the bud grafting piece can be as long as 1.3 cm ~ 1.5 cm with a little xylem. Cutting is controlled from late March to mid-April, and scions adopt single-bud branches. Then, all the incisions and seams are wrapped in plastic film to expose the buds. Abdominal transplantation can be performed from March to 10. First, cut a wide incision with cortex from top to bottom from the ground 10 cm to 15 cm, the length is 1.5 cm ~ 2 cm, and the xylem is deep, then cut off the cut rootstock skin 1/3, and then insert the scion. Scion cutting is the same as single bud cutting, except that the long section should not be cut too heavy, just look at the xylem. When the scion is inserted, it must aim at the cambium of the rootstock section, reach the bottom of the incision, and then tie it.
2. When using the orange area at the northern edge of the garden as a commercial base to develop citrus production, we should first choose a place with a large water body (such as a lake) nearby or located in the inversion layer of the hillside, which is sunny and leeward in winter and has superior microclimate conditions, and avoid building the garden in the tuyere where cold air is easy to flow or in a stagnant low-lying valley. Before or at the same time of planting, windbreaks should be built first. Tree species should be cold-resistant evergreen trees such as Coral Tree (france holly), Ligustrum lucidum and Heather. If it is planted sporadically in front of and behind the house, you can choose a place that is easy to prevent cold in winter. Citrus is not strict with soil. It can be planted in places with deep soil layer, good drainage and low groundwater level.
The suitable period for planting citrus in northern orange area is the relative dormancy period when the seedlings are not frozen. Autumn planting should be done earlier, and it will end about 1 month before the autumn shoots stop growing and the severe cold comes. After planting, do a good job in cold protection such as irrigation and soil cultivation. Trees can easily freeze to death if planted too late. It is safe to plant citrus before germination in spring and after the temperature rises steadily (from mid-March to early April). You can also plant a small number of seedlings before the spring seedlings stop growing and the summer seedlings are pulled out in the rainy season. Some orange areas have the experience of raising 2 ~ 3-year-old seedlings and planting them with soil. After planting, the survival rate is high, the growth is fast, the fruit is early and it is not easy to be frozen. This experience is worth popularizing.
Citrus is suitable for close planting. The planting distance varies with varieties, rootstocks and soil fertility. Generally, the row spacing of trifoliate orange rootstock is about (2.5 ~ 3)m×3 ~ 4)m, and that of other citrus varieties is (3 ~ 4)m×4 ~ 5)m m ... The hills should be dense and the flat land should be thin. In order to improve the early yield, citrus can also be planted densely first and then sparsely. When planting in pieces, we should also consider the collocation of varieties.
(5) shaping and pruning
1. The shaped citrus is dry and weakly branched, and the shaping can conform to its branching habit, so as to cultivate a natural happy tree without a central trunk or a natural round-headed tree with an inconspicuous central trunk.
Mandarin orange has an open crown and strong photophobia, and mainly bears fruit from peripheral branches. The periphery of the crown requires concave-convex surface and good light transmission, so it is most suitable to use natural happiness trees. Usually, the stem is fixed at a height of 40 cm ~ 50 cm, the lower part is 25 cm ~ 30 cm as the trunk, and the upper part is alternately divided into three main branches, keeping a certain branching angle, and other buds and branches are smoothed as soon as possible. In the future, on the main branch about 30 cm away from the main branch, the auxiliary main branch is selected obliquely outward, and 2 ~ 3 main branches are cultivated alternately in turn, so that there are obvious layers around the crown. The pattern of the whole tree is the same as that of peaches of deciduous fruit trees. In plastic surgery, techniques such as pulling branches are also used to adjust the branch angle.
Some varieties with erect branches, such as ponkan and cinnabar orange, are used to natural round-headed trees. This tree shape is basically refined and adjusted according to the branching situation of citrus itself. After the seedlings are fixed, 3 ~ 4 robust and evenly distributed main branches are selected, and a certain number of auxiliary main branches are arranged on them to occupy space. Every year, the main branches and auxiliary main branches keep branching and extending outward, and finally form a natural round crown. This kind of tree pruning is light and easy to shape, but the branches are dense and the affiliation is often not obvious. After the full fruit period, the ineffective volume of the inner chamber is large and the green leaf layer is thin, so it is necessary to prune and shrink the big branches properly, otherwise the yield will not be improved easily.
2. Pruning and shoot control pruning are mainly carried out in northern orange area before germination in spring. Citrus leaves carry out photosynthesis all the year round, and there are many flower buds on the upper branches, so the pruning amount must be light, generally not exceeding 1/5 of the total number of leaves.
In the first three years of young tree shaping, it is mainly to cultivate backbone branches and expand crowns quickly. The extension branches of backbone branches at all levels should be cut short as required, generally 40 cm to 50 cm. All buds should be picked when they appear to avoid fruit hanging. Or spraying gibberellin with the concentration of100-200 ppm (100-200 ppm) for 2-3 times before the differentiation of citrus flower buds in late autumn and early winter, and basically not flowering in the next year.
After entering the fruiting period, in addition to timely thinning, thinning, dense and long branches, the fruiting mother branches should also be appropriately pruned according to the specific conditions to balance the contradiction between fruiting and growth. Generally, annual trees should be cut short, and other branches should be cut and thinned appropriately to promote the development of new shoots; Young trees should be reserved as much as possible for the mother branches to bear fruit, and should be lightly cut. Results After fruiting, strong mother branches with new branches can germinate below the fruiting position, and after fruiting, they can shrink to the place where new branches occur. If the mother branch is not stripped in the current year, the original bearing mother branch can be thinned after bearing fruit. Pruning fruiting branches, after picking fruits from leafy fruit branches, the year of robust growth can be directly transformed into fruiting mother branches, which should be retained; If it can't be transformed into fruiting mother branches, it can be cut short appropriately to make it fresh and form new fruiting mother branches again. Leafless fruit branches will dry themselves after picking and can be cut off.
The drooping branches that have borne fruit and the mother branches with weak fruit should be pruned properly to facilitate the cultivation of new mother branches. However, the drooping long branches of mandarin oranges have a certain ability to bear fruit continuously, so it is advisable to shrink more and cut more after bearing fruit. When the growth results of the fruiting branch group decrease, the part of the 3-4-year-old branch can be contracted to promote the regeneration.
When pruning, we should also pay attention to the differences of varieties, tree age, tree vigor and fruit quantity, and use them flexibly.
In order to adjust the growth of citrus shoots in time and reduce nutrient consumption, it is necessary to wipe buds, control shoots and pick cores frequently during the growth period. According to the standard of "five to two, three to one", the branches that are too weak and too strong are erased, and the robust and moderate branches are retained, so that the nutrients are concentrated, the branches are evenly distributed and thrive. Summer shoots occur more during the young trees, which will affect the fruit. Most northern orange areas use the growth of spring shoots and early autumn shoots to cultivate fruiting mother branches, and summer shoots can be erased at any time when they sprout. In order to save labor, we can also spray 250-750 ppm (250-750 ppm) adjusted phosphine solution for bud control in summer or 3-4 days before and after bud germination in late autumn. The erasing of summer shoots will end in mid-July, and shoots can be released after late July. Heavy fertilizer should be applied once 15 ~ 20 days before the bamboo shoots are released, so that the early autumn bamboo shoots can germinate orderly. After putting the tender branches, we should dilute the weak and stay strong, and dilute the branches appropriately.
In addition, when the spring shoots bloom, some lush vegetative branches of the spring shoots can be erased to improve the fruit setting rate. No matter spring shoots, summer shoots and autumn shoots, when they grow to 25 cm ~ 30 cm, they should be pulled out to enrich the growth or promote the branches to form good fruiting mother branches.
(6) Soil, fertilizer and water management and others
1. Soil, fertilizer and water management Only when the root system grows well can the citrus bear normal fruit and improve the cold resistance of the plant. Especially in citrus orchards in hilly areas, we should pay attention to deep ploughing and soil improvement, expand the tree tray year by year, and make the roots go deep into the soil layer to avoid drought and freezing injury in winter. Where water is scarce, ground cover should be popularized to create a good environment for the growth of citrus roots.
Citrus needs a lot of fertilizer, and the trees should be fertilized 3 ~ 4 times a year during the full fruit period. The first time was post-harvest fertilizer, which was applied as base fertilizer during 10 ~ 1 1. Medium-maturing and late-maturing varieties can be applied one week before fruit picking. The function is to restore tree vigor, increase storage nutrition of trees, improve cold resistance of plants and promote flower bud differentiation. Fertilization accounts for 40% ~ 50% of the annual fertilizer, mainly organic fertilizers such as pig manure, cake manure and human manure, and can also be properly combined with quick-acting fertilizers. At one time, the germination accelerating fertilizer was applied 1 ~ 2 weeks before the spring weather turned warmer, which promoted the orderly germination and healthy growth of spring shoots, delayed the shedding of old leaves and improved the fruit setting rate. This topdressing is mainly available nitrogen fertilizer, combined with phosphorus and potassium fertilizer, with more application for weak trees and less application for strong trees. The second is the strong fruit fertilizer, which is applied after the physiological fruit drop stops in July. Young trees can be combined with topdressing and irrigation. Fertilization period should not be too late, otherwise it is easy to promote late autumn shoots. Fertilizer types, nitrogen, phosphorus and potassium. After that, it is necessary to control fertilizer and water to improve the cold and wintering ability of trees.
Fertilization amount is generally estimated according to fruit yield. Each production of 100kg citrus fruit requires 0.5kg ~ 0.7kg of pure nitrogen, 0.3 kg ~ 0.4 kg of phosphorus (P2O5) and 0.4 kg ~ 0.5 kg of potassium (K2O). High-yield fields can be topdressing once after flowering, or topdressing outside the roots. Young trees and strong trees with delayed fruiting should reduce the amount and frequency of fertilization, especially nitrogen fertilizer.
The soil in orange orchards should always be moist. If there is summer drought or autumn drought in summer and autumn, it should be irrigated in time to meet the needs. The roots of Fructus Aurantii are not tolerant to dampness and waterlogging. In rainy season, low-lying orange orchards should be drained by sweat ditch to avoid root rot or inhibit overground growth.
2. The phenomenon of anti-freezing citrus flowers falling is serious, and different measures should be taken according to the reasons. For weak trees with poor growth, it is necessary to strengthen fertilizer management, sparse flowers and fruits, maintain a constant leaf-fruit ratio, and do a good job of leaf protection in winter and spring. For flowering and fruit dropping caused by flourishing leaves, especially excessive germination of summer shoots, it is necessary to properly control fertilizer and shoots. For young trees with many flowers and flourishing growth, from bud stage to withering stage, the flourishing branches can be cut off for 2 ~ 3 times with a sharp knife to temporarily inhibit growth. In addition, spraying 50PPm gibberellin at the end of flowering, spraying again every 15 ~ 20 days, or spraying 100 ppm sodium lignosulfonate solution at the bud stage and fruit-setting stage in June can effectively improve the fruit-setting rate and achieve the purpose of protecting flowers and fruits.
Under the attack of periodic cold current, the orange area on the northern edge often appears different degrees of freezing damage. In addition to strictly selecting favorable site conditions, building shelter forests, selecting cold-resistant varieties and cold-resistant rootstocks, autumn shoot growth should be ended in time, fruit yield of trees should be appropriate, and fertilizer should be applied in time after harvest. ~ Some emergency temporary measures to protect trees and reduce the temperature difference, such as whitewashing branches, sokcho, tying mud rope, raising soil at the height of root neck, dusting tree trays, spreading grass or covering with plastic film, watering before freezing, smoking during frost period, etc. It also has a certain cold-proof effect and can be selected for application. Large antifreeze can also be used as steam inhibitor and heat preservation agent. Before freezing, the citrus reticulata in front of the house and behind the house was built into a double-layer triangular shed with straw and plastic sheets to cover and protect the citrus reticulata. The cold protection effect is good, and it will be taken off when it is warm in spring.
(seven) the main pests and diseases and their prevention and control
1. There are many diseases and insect pests on citrus, and the common diseases are canker, anthracnose, scab and resin disease.
(1) canker: it is a bacterial disease, which is the most harmful to seedlings and young trees and often causes a lot of deciduous leaves; It will harm the buds, leaves and fruits of adult trees. Pathogens overwinter on diseased shoots and leaves. Prevention and control methods: strengthen quarantine, establish disease-free nursery to prevent scions and seedlings from spreading with bacteria, or buy aseptic seedlings for planting. Do a good job in clearing the garden. Chemical control can be done once in spring shoot length 1 cm and after flowering 10, 30 and 50 days respectively. The effective agents are 70% mancozeb 500 times solution, 1: 2: 200 times bordeaux wave, 600 units/ml ~ 800 units/ml agricultural streptomycin mixture 1% alcohol, etc.
(2) Scab and anthracnose: Both are fungal diseases, which harm new shoots, leaves and fruits, and pathogenic bacteria overwinter on diseased shoots and leaves. Control methods: In addition to clearing the garden in winter to reduce the source of the disease, Bordeaux mixture, bactericide or Tobuzin can also be used to protect new shoots and young fruits during the growing season.
(3) Resin disease: The occurrence of this disease is closely related to the freezing injury of citrus. The prevention and control measures should be to strengthen the tree potential and prevent the branches from freezing. After the disease, you can scrape the diseased spots and their surroundings with branches vertically and horizontally until they reach the xylem, and then smear them with 50% thiophanate or 50% carbendazim 100 times solution, or smear them with 40 1 antibacterial agent 50 ~ 100 times solution or resin mesh for 2 ~ 3 times continuously, with each interval/kloc-0.
2. The main pests are many kinds of scale insects, red spiders, rust ticks, leaf miners and bud maggots.
(1) Scale insects: At present, scale insects are the most common and serious in China. Three generations a year, overlapping generations. It often causes fallen leaves and dead branches, weakens tree vigor and reduces fruit quality. Arrow scale overwinters as a female adult. It can be known that the first generation nymphs were sprayed with 40% omethoate 500 times during the incubation period, and then sprayed again 20 days later, or sprayed with 20% chlorpyrifos 1000 times and 40% isocarbophos 500 times.
(2) Red spider and rust tick: the former harms leaves, while the latter mainly harms fruits. Two kinds of mites have many generations every year. Control methods: Spraying 0.8 ~ L lime-sulfur mixture before citrus germination to inhibit overwintering insect population, and spraying 20% dicofol 800 ~ 1000 times, 73% propargite 2000 ~ 3000 times or 5% Nisolone emulsion 2000 times according to the insect situation during the growth period.
(3) Liriomyza sativae; Young branches and leaves are the most seriously damaged leaves. Eggs are laid on tender buds. Prevention and control methods; Mainly in summer and autumn, shortly after a large number of new buds germinate, spraying drugs continuously for 2 ~ 3 times in time (spraying interval is about 10 ~ 14 days). The best insecticides are pyrethroids, such as 20% metronidazole emulsion 2500 ~ 3000 times, 2.5% mirex 6000 ~ 8000 times or 20% mirex 5000 times. It can also treat Papilio larvae.
When controlling citrus diseases and insect pests, we should pay attention to the alternate use of chemicals and the protection of natural enemies.