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Citrus: Nutritional, Economic and Medicinal Wonders
Grown year round, the citrus group is composed of various species that are of great nutritional, economic and medicinal importance, including sweet oranges, grapefruits, lemons and limes. Primarily grown for the consumption and juicing of their fruits, they also are great facilitators of international trade and their exportation can bring great wealth to a country.
Production of citrus requires specific skills, however, which can only come through specific training and skill building.
This article will give you details specific to citrus production, including how to:
- select a site for production;
- prepare a nursery for citrus plants;
- prepare a seed bed;
- provide rootstock;
- prepare a budding bed and carry out budding;
- transplant to a field; and
- manage the field up to harvesting and storage.
Preparing a Site of Production
First, prepare a rich, deep loamy site for your orchard. Citrus will survive and do rather well, however, in soils too shallow and poorly aerated for other tree crops to survive.
On the other hand, citrus trees may be badly injured in soils a little more shallow and wet, whereas another fruit like mangoes would thrive.
Any site selected should be level or only slightly sloping. It should also be protected from strong winds either naturally or by the establishment of windbreaks.
For a primer on best nursery practices, check out this article on How to Prepare and Manage a Functional Plant and Tree Nursery.
In addition to what you will learn in that guide, you will need to select an area with good shelter from winds.
In areas of heavy rainfall, a gently sloping ground must be chosen for thorough drainage, as you must avoid water logging conditions. Look for deep and well-drained soil.
Seed Bed Preparation and Sowing
Cultivate the soil deeply and then apply fertilizers as a base dressing as follows:
- Super phosphate: 60g/m2
- Sulphate of ammonia: 30g/m2
- Potash: 30g/m2
Your seedbed should be about 1.2–2 m wide and as long as is practically convenient for you. You will need to raise the bed to roughly 15 cm above the surrounding ground level.
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You should be careful about using organic manure though, because it might introduce disease organisms.
Sow your citrus seeds in either seedboxes or in nursery beds as single seeds spaced at 3 x 6 cm. Pick out the seedlings when they are 3–6 cm in height into care baskets or poly bags that you have filled with fertile topsoil.
Rootstock Seed Planting
Plant the seeds of the desired rootstock. Rough lemon seed is usually used (sour orange can be used also) and planted in rows about 25 cm apart on the bed and about 8 cm within the row. You may drill the seeds and thin to about 8 cm apart later.
You will need to mulch the seedbed with groundnut (peanut) husk or some other suitable material. Apply plenty of water but avoid undue moisture, otherwise fungus disease might attack the seedlings.
Transplant to budding bed at about four months after sowing.
The Budding Bed
Set seedlings in rows 45 cm apart and 25 cm within the row. Mulch heavily with dry grass, leaving a small area around each seedling to reduce the danger of disease infection from the mulching materials.
Water the plants regularly. Each plant should get about a gallon of water per week. Apply about 149 of sulfate of ammonia and 149 of muriatic of potash per seedling every eight weeks.
After 7–12 months on the budding bed, the seedlings are ready to be budded.
When to Begin Budding
Budding is better done at the beginning of the rains or at the end of the rains, but not at the height of the rainy season. This is because disease organisms grow very easily during the rains.
You may bud your tree crop during the dry season, provided watering or irrigation facilities are available. The advantage of budding in the dry season is that you can regulate the amount of water the budded trees receive.
Budding is carried out in the cool hours of the morning or in the evening at a height of 25–30 cm from ground level on the prepared seedling rootstock. You should avoid budding during the hot hours of the day and during heavy rains.
Practice regular care on your budded stocks until they are old enough for transplanting into the field.
Most Popular Methods of Budding Used in Citrus
- Inverted “T” budding
- “T” or Shield budding
- Side budding, similar to side grafting in mango, has just been discovered in IAR, Samaru. (It is yet to be published but it is about 75–80% successful, all other things being equal.)
You may use two methods in transplanting your tree: the “bare-root system” or the “ball of earth” method.
The “ball of earth” method is generally better, since a lot of soil is left on the roots—thus transplanting shock is greatly reduced. If the “bare root system” must be used because of transport difficulty with the “ball of earth” method, the roots must be dipped in a “slurry” mixture of soil, clay and water in a suitable consistency.
You should plant your seedlings into the orchard at the beginning of the rainy season (May–June). Dig your planting holes 1 m x 1 m x 75 cm or as appropriate about one week before transplanting if possible.
You should half-fill the planting hole with top soil mixed with rotten compost or topsoil with high organic matter content.
Put the seedling in position with one operator holding it upright and in position in the hole, and the other operator being responsible for arranging the roots properly (for seedlings planted with naked roots). After proper filling, the second operator should consolidate the soil around the seedling to ensure that air pockets are completely excluded from the planting zone.
You must allow adequate planting distances, which are essential for economic productivity of citrus. Use recommended spacing for citrus, which is 10 m x 10 m.
Orchard planting is a very delicate and extremely important operation. Those who do the planting should be selected on the basis of carefulness and be trained in correct ways of planting.
It would be wise to apply nitrogen, phosphorous, potassium and magnesium. Where the trace element has been found to be deficient (they are not normally deficient) by foliar analysis, for example, the elements of manganese, molybdenum, boron, etc. should be supplied if necessary by spraying.
Ensure that the fertilizers recommended by your local agricultural organization for your zone are used.
Citrus requires little pruning, and overdoing it is likely to result in reduced yields. You should therefore limit it to removal of dead wood, overly vigorous branches and suckers.
Sometimes it might be necessary for you to remove overly dense growth to open up the trees for sunshine and wind to dry the trees in areas of heavy rainfall.
This will reduce the infections by gummosis and foot rot fungi.
Citrus trees deplete soil water throughout the year; long water deficits therefore impair tree growth and fruit set.
Some short periods of water deficit are required for flower initiation, however. Even though the drought may have lasted just long enough to start flower induction, you will find that oranges will not blossom until the rains begin or you irrigate the orchard.
Citrus trees tend to drop their fruits excessively because of great daily water deficits, especially parthenocarpic fruits (fruits that develop without fertilization) such as Washington navel oranges, sweet oranges, and Marsh seedless grapefruit.
It is believed in the citrus industry that when seeds are processed with fruits in the extraction of juice, the natural sweet taste of oranges is tampered with. A situation where there are no seeds in the fruit is a welcome development. Having to remove seed mechanically or manually before fruit extraction also necessitates extra labor and cost.
Harvesting and Storage
Citrus begins to bear fruits around three to five years after planting in the field, depending on the species, variety and method of propagation. Vegetatively propagated materials come into fruit season earlier than seedlings.
In citrus, you will discover that the color of the fruit is often green when fruits are not mature in many cases (Nigerian green sweet is an exception). On maturity, the fruits begin to ripen, during which period the colour turns yellow or orange.
You should harvest when mature fruits with considerable green will ripen if you store them at 60°F without artificial treatment (like ethylene). Only fruits that are ripe at harvest keep at low temperatures like 45°F.
Avoiding Fruit Loss
It is very important that you do not bruise the fruits while harvesting, otherwise molds can gain entrance and cause foot rot, and this is the greatest source of loss after harvest.
Citrus fruits are easily perishable after ripening. To ensure that fruits are not lost through over-ripening, fruits should be harvested immediately once they are ripe and delivered to consumers, processors or retailers.
In some cases, you may need to store your fruits for some time while awaiting markets or transportation to distant markets. Under such circumstances, you may need to harvest the fruits a short time before full ripening. The time interval between harvesting and full ripening depends on the length of time the fruits are to be stored or the length of time required for transportation.
When fruits are destined for distant markets, you should harvest when they are physiologically mature but before ripening. Such fruits generally ripen en route to the market, or they are treated with chemicals (ethylene, etc) to ensure uniform ripening.
Pests and Diseases
You will likely experience a number of insect attacks on your citrus plants, including scale insects, aphids, mealy bugs, mites, fruit moths, beetles and others.
You will likely need to use insecticides. In spraying citrus plants with insecticides, however, you should use caution. Certain persistent insecticides such as DDT could do more harm than good, as they kill both pests, predators and parasites. Please consult a specialist before the application of chemical sprays.
Citrus diseases may be caused by viruses, bacteria, fungi, algae, nematodes and plant parasites. Citrus plants are also known to suffer from a number of deficiency diseases.
Major Diseases of Citrus
- Tristeza: This is a virus disease of citrus. It is not controllable, but it is preventable by using the right rootstock like rough lemon.
- Anthracnose: Major symptoms are leaf blight, twig blight and staining. It can be controlled by proper sanitation and spraying with copper fungicides. You can also use disease-resistant varieties if available.
- Scab: This is caused by fungi. The main symptoms are whitish scabs on the leaves twigs and fruits of citrus. The main method of control is proper farm sanitation. You may also spray with fungicides such as Captan and Bordeaux mixture.
- Footrot or brown rot: This is known simply as citrus gummosis. It is caused by Phytophthora spp. It kills the bark on trunk and roots, which eventually kills plants. Control methods generally involve treating plants with effective fungicides.
- Sooty mold
- Algal leaf spots
- Mineral deficiencies
In most cases, you do not need to worry much about the minor diseases, as adequate farm sanitation should largely keep them in check.
This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.