The Organic Farming Technique for Planting and Caring for Orange Trees

1. Soil

Oranges are one of the versatile plants that can thrive in various types of soil. However, the most suitable soil for planting oranges is loamy soil with a pH level ranging from 5 to 6.5. Depending on the terrain (whether it’s high or low, well-drained or poorly drained), choose between bed planting or mound planting. Before planting, consider installing windbreaks, designing protective fences, establishing drainage systems, and setting up irrigation systems.

2. Light and Temperature

The ideal temperature ranges from 18 to 35 degrees Celsius. Light is one of the crucial factors for orange trees. It determines the quality of sweet, crisp, and aromatic oranges.

3. Orange Varieties

Choose seedlings that are over 30 cm tall, vigorous, with green, sturdy leaves, and free from pests and diseases. There are two main types of orange varieties: cutting and grafting (not using seeds as planting materials). Cutting varieties have the advantage of early fruiting but tend to have a shorter lifespan with weaker root systems. Grafted varieties, on the other hand, have stronger root systems, resulting in healthier, sturdier trees with longer lifespans.

4. Planting

a. Planting Seasons

• Spring Crop: February – April
• Fall Crop: August – September

b. Soil Preparation for Orange Trees

Before planting, clear the area of weeds, plow thoroughly to loosen the soil. Deep plowing helps the soil retain moisture effectively. The suitable planting density for grafted orange trees planted on seedlings is 400 trees/ha, with a planting distance of 4m x 4.5m. For grafted cutting varieties, the appropriate planting density is 1000 trees/ha with a planting distance of 3m x 3m.

b. Planting

Dig planting holes with dimensions: 1m x 1m x 1m. When digging, separate the topsoil layer, mix the lower soil layer with organic bio-fertilizer VN3 from Suối Hai Manufacturing and Trading Co., Ltd., lime powder, and phosphate. Then fill the hole so that it is 20 – 30 cm higher than the ground level. When planting, dig a hole in the center of the mixture, place the seedling’s root ball down so that the surface is 3 – 5 cm higher than the mixture. Then backfill with soil up to the root ball surface, compact gently, and water. When placing the plant, rotate the graft union in the direction of the prevailing wind to avoid branch breakage, and stake the plant to prevent wind damage if necessary. It’s advisable to plant oranges in the late afternoon when the weather is cool, which benefits the plant’s growth. Water daily for the first 10 days, then provide sufficient moisture every 3-5 days for a month.

5. Care Techniques for Orange Trees

5.1. Fertilization

* Fertilization principles: It’s essential to provide nutrients to the trees by fertilizing throughout the planting period, especially when the trees flower and bear fruit. The amount of fertilizer depends on the variety, climate, and soil type to ensure suitability. Before planting, clear the weeds and plow the land thoroughly to loosen the soil. Deep plowing helps the soil retain moisture well. The appropriate planting density for grafted orange trees seeded on the rootstock is 400 trees/ha, with a planting distance of 4m x 4.5m. For grafted orange trees, the suitable planting density is 1000 trees/ha with a planting distance of 3m x 3m.

• Type of fertilizer: Mineral organic fertilizer SH01 and organic microbial fertilizer VN3 from Suoi Hai Manufacturing and Trading Company
• Dosage:

Note: pH of soil > 6.5 does not require lime application; Each fertilization should be combined with weed management, root cultivation, watering, and mulching around the base of the tree.

5.2. Basic Establishment and Commercial Care Period

• Weeding: In the first years, when the trees are still small and their canopies have not yet closed, it is necessary to keep the base free of weeds. In flat or slightly sloping areas, green manure crops should be planted between the rows of trees to cover the soil, retain moisture, control weeds, provide green manure to improve the soil, and supply nutrients to the trees.
• Intercropping: On sloping land, plant a double row of green manure shrubs such as muong, Flemingia, Acacia, and legumes between the orange rows to prevent erosion and supply organic matter on-site. Use 20-25 kg of green manure seeds per hectare. The remaining empty land in the strip can be sown with herbaceous legumes like cowpea, Stylo grass, and peanut grass to cover the soil, retain moisture, and control weeds. Green manure crops are usually sown before or immediately after planting the orange trees.
• Pruning: The framework of the tree canopy should consist of three primary branches (C1). Each C1 branch should have 2-3 secondary branches (C2). The primary branches grow from the main trunk, 50 cm above the ground, at an angle of 60-80 degrees. The secondary branches grow from the primary branches at an angle of 10-20 degrees, with the length of the primary branches controlled to 50-60 cm. The tertiary branches grow from the secondary branches at an angle of 10-20 degrees. The fruit-bearing branches are the quaternary branches, evenly distributed around the canopy.
• Pruning: Prune the trees three times a year, as follows:
  • First session: Prune after harvesting. Remove all branches inside the canopy, small branches, weak branches, diseased branches, some vigorous branches, and branches that intersect each other. Combine pruning with field sanitation and burn all disease remnants in the garden.
  • Second session: Prune in the spring, during the flowering and fruit-setting period. Remove weak branches, branches with small flower clusters, diseased branches, and branches growing inside the canopy.
  • Third session: Prune in the summer, during the fruit growth stage. Remove diseased branches and thin out small and deformed fruits.
• Watering:
  Regular watering is essential for the healthy growth and development of the trees. In mountainous provinces where the weather is often dry, it is crucial to ensure adequate soil moisture. Employ methods such as drip irrigation, sprinkler irrigation, or water-saving irrigation techniques. If water supply is controlled, the best method is to fill shallow trenches with water, allowing it to seep into the soil, then drain the excess water after a day.
• Harvesting Technique:
  Harvest when the fruit turns yellow. Harvest on sunny, dry days; avoid harvesting right after rain or on foggy days, as the fruit is prone to rot. After harvesting, store the fruit in a cool, well-ventilated place. Do not store the fruit for more than 15 days post-harvest to maintain its commercial value. For longer storage, keep the fruit in a cool, ventilated area.

5.3. Pests and Diseases of Oranges and Control Methods:

• Leaf Miner Phylocnistis citrella
  • The adults lay eggs on the underside of young leaves. The larvae bore into the lower epidermis, creating winding tunnels of white-silver color. The larvae pupate inside the rolled leaves. The lifecycle of the leaf miner is short, ranging from 17 to 23 days.
  • Control: Spray biological products, such as the herbal insecticide Anisaf-01, or chemical products (Polytrin 440EC at a concentration of 0.25%). Spray when the young shoots are 1-2 cm long.
• Weevils: Hypomeces squamosus and Platymycterus sieversi
  • Hypomeces squamosus is green-yellow and larger than Platymycterus sieversi, which is off-white. When disturbed, the weevils either hide or feign death and fall to the ground. Adults mate during the day, laying eggs in batches of 3-5 in tree bark crevices or the edges of dry leaves. The larvae hatch and fall to the ground, where they develop. Adults emerge after rains in April-May and July-September.
  • Control: Spray biological insecticides (such as the herbal insecticide Anisaf-01) or chemical insecticides (Supracide at 0.20 – 0.25%).
• Shoot Borer: Chelidonium argentatum
  • In April-May, adults lay eggs singly in the axils of young leaves and shoot tips. The larvae bore into the branches, creating spiral-shaped tunnels. Initially, the tunnels extend outward, then turn inward towards the trunk where the larvae pupate.
  • Control: Spray biological insecticides (such as the herbal insecticide Anisaf-01) or chemical insecticides (Supracide at 0.2 – 0.25%) when new shoots appear, or inject Ofatox 0.1% into the bored holes in the branches and seal the holes with clay.
• Stem Borer: Nadezhdiella cantori Hope
  • The adult is dark green with white spots. It lays eggs singly in the cracks of the tree. The larvae bore into the stem, creating winding tunnels from bottom to top, pupating inside the stem.
  • Control: Maintain garden hygiene, keep the base of the tree clean. Regularly apply lime water to the base to limit adults from laying eggs on the stem. Inject Supracide 0.2 – 0.25% into the holes with larvae, then seal the bored holes with clay to kill the larvae.
• Fruit Piercing Moth Group: Othreis fullonia, Ophiusa coronata, Ophiusa tirhaca
  • The adults are active from dusk to midnight, feeding on the sap of ripe oranges. Fruits pierced by these moths will rot and eventually fall off.
  • Control: Set up lure traps with insecticide to kill the moths, 10 traps/ha.
• Fruit Fly: Bactrocera dorsalis
  • The adult fly is about 4 – 5 mm long, reddish-brown, with yellow veins. The adult female lays eggs by piercing the fruit, and the larvae hatch to feed on the fruit flesh, developing into maggots inside. Fruit flies cause severe damage in August-September. Infested fruits often drop prematurely.
  • Control: Use Methyl eugenol + Nalet bait to eliminate adult flies.
• Thrips
  • Thrips live in colonies, sucking sap from flower clusters or young plant parts. The excrement of thrips creates a favorable environment for the development of black sooty mold. Thrips cause flower and young fruit drop, deformation of young shoots, and leaf curling.
  • Control: Spray biological insecticides (Herbal Insecticide Anisaf – 01) or chemical insecticides like DC Tron Plus 0.5%, Supracide 0.2% when thrips infestation is detected.
• Citrus psyllid: Diaphorina citri
  • The adult psyllid is brownish-gray, measuring 2.5 – 3 cm in length. The female psyllid lays eggs on newly emerged shoots, with the potential to lay up to 800 eggs. Adult psyllids are agile, while the yellowish nymphs are less mobile.
  • Control: Spray DC Tron Plus 0.5% oil, Sherpa 0.2% for prevention.
• Red spider mite: Panonychus citri, Tetranychus citri
  • The red spider mite measures about 0.5 mm in length, with a square-shaped body, dark red (Tetranychus) or bright red (Panonychus citri) in color. The body is sparsely covered with long white or slightly yellowish hairs. The spherical or onion-shaped eggs of the mite are bright red. The mites lay eggs along the leaf veins on both sides of the leaf.
  • Control: Spray Abamectin: 0.3%, DC Tron Plus 0.5%, Pegarus 0.2%, Saromite 0.15%.
• Huanglongbing (HLB) or Citrus Greening caused by Liberibacter asiaticus
  • The infected trees show symptoms of “yellowing veins with green leaves”. The disease typically starts from individual branches, with leaves gradually falling off and branches dying. On the infected branches, the fruits are small, misshapen, pale, and sour.
  • Control: Remove the diseased trees. Ensure proper care for the citrus orchard, interplanting with guava to repel psyllids. Alternatively, control using microbial products containing antagonistic bacteria and fungi like Trichoderma.
• Citrus Canker: Xanthomonas citri subsp. citri
  • Symptoms: Initially, on the leaves, the disease appears as translucent oil-like droplets, which later spread to form circular or irregularly shaped light brown lesions with yellow halos. The disease spreads rapidly under high temperature and humidity conditions. Infected trees shed leaves extensively, branches dry up, and eventually die. The growth of the tree is stunted, and fruits drop prematurely.
  • Control: Control using microbial products containing antagonistic bacteria and fungi like Trichoderma, or spray with a 1% Bordeaux mixture solution.
• Gummosis: Phytophthora sp.
  • The disease primarily affects the fibrous roots at the interface between the above and below-ground parts. In infected trees, leaves turn yellow, and gum oozes from the diseased lesions on the trunk.
  • Control: Control using microbial products containing antagonistic bacteria and fungi like Trichoderma, or apply a 2% Aliette solution or a 3% Bordeaux mixture solution to the tree trunk.

Note: Only use chemical pesticides when absolutely necessary, but adhere to the principles of targeting the right pest, at the right time, with the right concentration and dosage, and in the right way. Emphasize pest management through a synthesized process combining agronomic practices, field sanitation; manual methods such as insect trapping; biological and chemical measures.