Key Technical Points for Spring and Summer Field Management of Navel Orange Orchards
Spring comes early in southern Jiangxi, warm and rainy. From March to June, navel oranges are in the phenological stages of spring shoot growth, flowering and fruit set, and the first and second physiological fruit drop. This is also the dangerous period when more than 10 kinds of pests and diseases, such as citrus flower bud midge, mites, scale insects, tortrix moths, longhorn beetles, anthracnose, resin disease, and canker, rapidly multiply, spread, and proliferate. The quality of orchard management at this time is the key period affecting navel orange yield and quality. With so many tasks to handle, the following three technical measures should be carried out well.
1. Clearing ditches for drainage and storing water to prevent drought
Navel oranges have relatively poor stress resistance during the flowering and young fruit stages. They fear both high-temperature drought and flooding and waterlogging, so special attention must be paid to strengthening water drainage and irrigation management in the orchard.
(1) Clearing ditches for drainage in navel orange orchards
According to meteorological data, rainfall in southern Jiangxi increases severalfold starting in April, reaching 203.5mm, and enters the rainy season. In May and June, rainfall further increases, reaching 256.6mm and 303.8mm respectively, and heavy rainstorms often cause disasters. This is a flood season. Therefore, terrace management should be done carefully, ditches should be cleared for drainage, and every ditch should be connected so that drainage flows smoothly. After rain, there should be no standing water in the orchard, ensuring normal root growth and development of navel oranges and a strong ability to absorb fertilizer and water. If drainage in the orchard is poor during the rainy season, soil oxygen deficiency occurs. When the oxygen concentration in the soil drops below 2%, navel orange roots turn black and rot. Under oxygen-deficient conditions, soil substances undergo reduction reactions, producing large amounts of toxic substances such as hydrogen sulfide and methane. When the hydrogen sulfide concentration in the soil reaches 3×10-6, navel orange roots are poisoned and die. In addition, standing water in the orchard also creates a high-temperature and high-humidity microclimate. According to scientific research records, within the suitable temperature of about 20℃, the incidence of navel orange anthracnose, resin disease, and canker is almost directly proportional to rainfall. This is because frequent rainfall and long rainfall duration favor the massive production and widespread spread of pathogen spores, causing disease epidemics. In mild cases, this causes navel orange leaf drop, flower drop, and fruit drop, weakens tree vigor, reduces yield, and lowers quality; in severe cases, it causes root rot, dead branches, dead trees, and orchard destruction.
(2) Storing water during the rainy season to prevent drought
While emphasizing ditch clearing and drainage to prevent waterlogging in the orchard during the rainy season, attention should also be paid to directing surface runoff during the rainy season into ponds, mountain pools, and reservoirs to store water for drought prevention. According to scientific calculations, in southern Jiangxi, if one cubic meter of water can be stored per navel orange tree on average, it can solve the water source problem for supplemental irrigation during the dry season.
2. Protecting flowers and fruits and thinning flowers and fruits
Navel oranges have a large flower quantity and poor flower quality, with severe flower and fruit drop. According to survey statistics, the fruit-setting rate of navel oranges is only 0.2%-1.7%. 98% of flowers and fruits drop at the bud stage, flowering stage, young fruit stage, and even mature stage respectively, which shows how important it is to implement flower and fruit protection techniques for navel oranges.
(1) Flower and fruit protection techniques for navel oranges
1. To protect flowers, first protect leaves: The leaves of navel oranges are organs for producing and storing organic nutrients. Flower organ development, spring shoot growth, flowering and fruit set, and early young fruit development mainly rely on nutrients stored in overwintering old leaves. Therefore, the more overwintering old leaves retained on navel oranges, the richer the nutrients stored in the tree body, the more spring shoots sprout, the faster they grow, the better the flower quality, the higher the fruit-setting rate, the faster the young fruits develop and expand, and the higher the per-unit yield and better the quality. In cultivation, through reasonable soil, fertilizer, and water management and successfully passing the pest and disease challenge, ensuring that old navel orange leaves overwinter safely, then reducing and delaying spring leaf drop, that is, prolonging leaf age, is crucial.
2. Controlling pests and diseases: The harm of pests and diseases to navel oranges is, first, weakening tree vigor and lowering the fruit-setting rate, such as sooty mold, felt fungus disease, foot rot, and mites, scale insects, and citrus leafminer. Second, they directly harm flowers and fruits, causing flower and fruit drop, such as canker, resin disease, flower bud midge, tortrix moths, and fruit-sucking noctuid moths. It is necessary to earnestly implement the technical measures of "prevention first, integrated control" to achieve the goal of protecting the tree and preserving the fruit.
3. Easing the conflict between shoots and fruits: For spring shoots, the first step is to promote them by applying spring fertilizer early and heavily, striving for early and abundant spring shoot growth, which helps reduce the second physiological fruit drop. If due to abnormal climate, delayed spring fertilizer application, or excessive nitrogen fertilizer, spring shoots grow excessively and cannot self-prune before flowering, timely pinching should be carried out to inhibit excessive growth. When there are too many new leaves, some nutrient branches at the top of the canopy and leafy flowering branches with four or more leaves should be removed. For mature trees, adjust the ratio of new to old leaves according to 1:1, and for young trees according to 0.7:1. However, spring shoots should not be removed too much, otherwise it will aggravate the second physiological fruit drop and hinder individual fruit development, resulting in many small fruits and failure to achieve high yield and quality. The handling of spring shoots should be completed 3-5 days before flowering; if later, the effect is poor.
Handling of summer shoots: For fruiting trees, summer shoots should be controlled, and careful application of fruit-protecting fertilizer is key. For mature trees, all summer shoots should be removed. Removing summer shoots is an important measure to reduce June fruit drop. For young trees, considering both fruiting and canopy expansion, only the middle and lower summer shoots should be removed, while the top summer shoots should be pinched.
4. Balancing endogenous hormones: Young trees produce many vigorous branches and have a low fruit-setting rate. In September and October, a piece of rice straw can be used to bend and tie the vigorous branch at the 1/2 point. Because the position of the vigorous branch tip changes, the level of promoting endogenous hormones in the entire branch is halved, while the level of inhibitory endogenous hormones doubles, thereby weakening the vegetative growth of the vigorous branch, promoting nutrient accumulation, and favoring flower bud differentiation. After January of the following year, the rice straw rots and loosens by itself. If the branch posture is still upright, bend the branch a second time before flowering in March or April to inhibit growth, which has a very good effect on protecting flowers and fruits.
5. Application of plant growth regulators to protect flowers and fruits:
① When 2/3-3/4 of navel orange flowers have fallen, spray a mixture of 50×10-6 gibberellin + 0.2% urea + 0.2% monopotassium phosphate + 0.1% thiophanate-methyl to protect fruits. In years or on trees with a small flower quantity, spraying may be considered earlier, when 1/2 of the flowers have fallen.
② Seven days after navel orange flowering or at the young fruit stage, spray young fruits with the fruit-spraying type enhanced liquefied BA+GA (product of the Chongqing Citrus Research Institute, same below), with each bottle (10ml) mixed with 15 kg of fresh water + 3 qian (15 grams) of thiophanate-methyl; or at the young fruit stage after flowering, use the fruit-coating type enhanced liquefied BA+GA, with each bottle mixed with 1 kg of fresh water, and coat selected well-growing, dark green young fruits once. The fruit-protecting effect can reach 70-80%. In mid-May, use yellow-fruit inhibitor, with each bottle mixed with 300 grams of water, and use a brush to dip the liquid and apply it to the navel, preventing navel yellow fruit drop.
(2) Flower and fruit thinning techniques for navel oranges
If navel oranges bear too much fruit, the tree body consumes too many nutrients, which not only affects full fruit expansion but also inhibits autumn shoot sprouting and flower bud differentiation, forming alternate bearing; at the same time, it also causes premature tree decline and shortens lifespan. In order to obtain high quality, stable yield, and relatively long-term economic benefits, navel oranges should also promote a reasonable load. While implementing flower and fruit protection, flower and fruit thinning should also be advocated, especially for weak trees and trees with a large flower quantity, where staged and batch-wise flower and fruit thinning should be emphasized even more.
1. Pruning to thin buds and flowers: During winter and spring pruning, short-cut and thin out some flower- and fruit-dropping branches and broom branches. This not only thins out a large number of inferior flower buds and flower buds but also renews fruiting mother branches and increases reserve branches, helping restore tree vigor and improve flower quality, fruit-setting rate, and fruit quality.
2. Staged and batch-wise fruit thinning: Throughout the entire fruit development process, remove diseased and insect-damaged fruits, deformed fruits, densely clustered fruits, small fruits, and thick-skinned large fruits in stages and batches. Finally, set the fruit load according to a leaf-to-fruit ratio of 50-60:1. This is an economical and effective measure for achieving high yield, stable yield, high quality, and high efficiency in navel oranges.
3. Pest and disease control and pollution-free food production
(1) Pest and disease control techniques for navel oranges
The warm and rainy environment and abundant food sources (spring shoots and young fruits) favor the breeding and multiplication of citrus pests and diseases. At the temperatures of April and May, the incidence of canker, anthracnose, and resin disease is almost directly proportional to rainfall; whether the first generation of scale insects, whiteflies, and tortrix moths is controlled well or not determines the annual pest population density and degree of damage; from early April, red spiders increase severalfold, and in May they enter peak occurrence. Rust mites move from old leaves to new leaves and then onto fruits, causing damage and forming the first peak. In addition, flower bud midges and weevils occur abundantly in early April, and Coleoptera pests such as scarab beetles, longhorn beetles, jewel beetles, and citrus flea beetles also emerge successively in May. Faced with the damage of more than 10 kinds of pests and diseases, if we adopt the method of spraying when insects are seen and applying chemicals when disease is seen, then making navel oranges into pollution-free food would be an empty talk. The policy of "prevention first, integrated control" must be implemented.
1. Strictly implement the plant quarantine system. Nursery stock, scions, and fruits transferred in and out must all undergo quarantine, with quarantine certificates issued, cutting off the transmission routes of dangerous pests and diseases.
2. Agricultural control: ① Select varieties and rootstocks with strong disease and pest resistance; ② Establish shelterbelt networks, and use intercropping or sod culture in the orchard to improve ecological conditions; ③ Strengthen field soil, fertilizer, and water management, cultivate strong tree vigor, and improve the disease and pest resistance of navel oranges; ④ Prune reasonably to directly remove some sources of disease and pest populations, improve canopy ventilation and light transmission conditions, and inhibit pest and disease multiplication; ⑤ Clear ditches for drainage, reduce orchard humidity, and inhibit the occurrence and spread of pests and diseases.
3. Physical control: ① Use the phototactic and chemotactic characteristics of pests to set up black light traps, yellow light traps, and poison baits to trap and kill adult scarab beetles and tortrix moths; ② Organize labor to capture and kill Coleoptera pests such as scarab beetles, longhorn beetles, and weevils.
4. Biological control: First, interplant plants such as ageratum, castor, perilla, and loofah in navel orange orchards to protect natural enemies of pests such as predatory mites, Amblyseius mites, green lacewings, ladybugs, and parasitic wasps; second, where conditions permit, artificially introduce, propagate, and release natural enemies of pests to use insects to control insects; third, use biological pesticides to control insects with fungi.
5. Chemical control: On the basis of strengthened investigation, grasp the occurrence patterns of pests and diseases in the orchard, clarify the primary and secondary targets, seize the weak links of pests and diseases, use pesticides reasonably, and eliminate pests and diseases timely, accurately, economically, and effectively before they cause losses. For example, in late April and early May, when the first-generation larvae of cottony cushion scale, arrowhead scale, chaff scale, and whiteflies are hatching abundantly or are in the 1st-2nd instar larval stage, and at the same time red spiders increase severalfold, rust mites move from old leaves to new leaves and then onto fruits to cause damage, and defoliating anthracnose occurs abundantly, and resin disease and canker attack fruits, first spray a mixture of 1000-fold supracide and 2000-type kocide for control. After 7-10 days, spray a mixture of 800-fold duoning, 1000-fold isocarbophos, and dimethoate, which can achieve control of primary scale insects and simultaneous control of mites and bacterial and fungal diseases, among other pests and diseases.
(2) Requirements for pollution-free fruit production
In the production and processing of pollution-free fruits, pollution of air, water sources, and soil in the environment, and excessive use of pesticides, chemical fertilizers, hormones, and other artificially synthesized chemical substances, seriously threaten people's health. Consumers demand high-quality, safe, and pollution-free food, and thus organic food, green food, and pollution-free food have emerged.
Organic food: refers to food that completely contains no artificially synthesized pesticides, chemical fertilizers, or hormones. It is the safest and highest-grade food for humans.
Green food: refers to food that follows the principle of sustainable development, is produced according to specific production methods, has been certified by a specialized agency, and is permitted to use the green food label trademark. It is divided into A and AA grades. Green food is pollution-free, safe, high-quality, and nutritious food. Because matters related to environmental protection are all labeled "green", and to highlight that this kind of food comes from a good environment, it is named green food.
Pollution-free food: refers to food whose production area environment, production process, and end products comply with pollution-free food standards and specifications, have been certified by a specialized agency, and are permitted to use the pollution-free label.
In June and July of this year, the Ministry of Agriculture held an important meeting in Ganzhou to formulate the "Quality Standards for Pollution-Free Navel Orange Fruit" and the "Division of Navel Orange Epidemic Areas". The issuance of these two documents marks that the state has made two very major decisions regarding the navel orange industry in southern Jiangxi, fundamentally resolving the potential crisis and worries about future troubles for navel oranges in southern Jiangxi.