Orange

Land Preparation:Orange

When a farmer wishes to establish a citrus plantation, certain actions need to be implemented to ensure the long term success of the plantation. One of these actions involve the initial land preparation which should be done prior to transplanting of the plant material (offshoots or tissue culture-derived plants).

The mechanical or initial soil preparation concerns mainly the preparation of a field for further detailed preparation such as irrigation system installation, hole preparation, etc. Actions, if applicable to the area, include:

(i) Bush clearing;
(ii) Removal of stones and rocks and;
(iii) Leveling of the soil.

Planting: Orange

1.1. Propagation

Most of the best citrus commercial varieties do not reproduce true by seed; they must be propagated through grafting.

These commercial varieties are  grafted onto rootstock of a specie known to give good results in terms of high growth vigour, compatibility with other varieties and adaptable to various soil conditions. The seed commonly used for raising citrus rootstock is the rough lemon (sour lemon). Budding is the most preferred method of citrus grafting.

When the rootstock plants of the selected rootstock are one year old or come to a buddable stage, the bud of a desired scion variety is budded at a height of about 25–30cm from the ground level. To ensure good budding success, the budding is done during the months  of active growth or when there is good sap flow in the plants. Thus, budded plant should be immediately irrigated. Bud wood of the scion must be taken from virus free indexed plants so that healthy, productive and true-to-the-type are produced.

1.2. Transplanting

The season A is the best time for transplanting. Planting holes of  0,8 x 0,8 x 0,8 m are prepared and the soil mixed well with 50 kg of organic manure.

The young trees are planted to the same depth as they were in the nursery. Once the tree has been planted, the soil must be firmly tramped down. A basin for irrigation is made around the tree which must be thoroughly irrigated immediately after planting. Irrigate again the following day to seal any cracks in the soil.

Spacing is chosen in relation to several factors: rootstock, climate, soil, cultural practices. Citrus trees can be planted at 4m x 4m or 3m x 5m spacing to accommodate as many plants as possible per unit area.

Planting depth is critical to the survival of citrus trees. The rootstock is somewhat resistant to foot rot disease, but the top is quite susceptible. If the bud union is too low with respect to surrounding ground, the tree could contract foot rot and die. The practice of scooping out grass and soil to form a large depression for ease of watering almost guarantees the death of a citrus tree.

Crop management:Orange

1.1. Weeding

Good weed control is essential for rapid establishment and vigorous growth of young citrus trees. Eliminate all existing lawn grass and weeds for several feet around the tree. As the spread of the tree increases, widen the grass-free area beyond the tree canopy or drip-line.

Weed control can be accomplished by mechanical means such as hoeing. Herbicides such as Roundup(TM) are excellent for control of existing weeds and pre-emergent herbicides like Diuron at 3 kg/ha twice at 120 days interval is quite effective to control weeds up to 280 days.

1.2. Intercrop

Leguminous vegetables like cow peas, French bean, peas, etc., may be grown in citrus orchards. Intercropping is advisable only during the initial three years. Moreover, Leguminosae plants are compatible with the citrus root system. Besides, they are able to accumulate nitrogen in their roots.

1.3. Training  

The trees are trained to a single system and any shoot emerging from the portion below the bud union should be nipped off regularly. The first year growth beyond height of 0.7–1m should be punched off to develop side shoot. Only 4–6 shoots having wide angle with the main trunk, all around should be allowed to grow up to 3–4m. Thereafter no training is required. Training of plants should be completed in first 3 years so that plants attain a mechanically strong canopy. The pruning in pre-bearing trees may be done at any time.

1.4. Pruning

Pruning of bearing trees though differs with variety. It consists of removal of dead, diseased and weak branches. Removal of water sprouts and suckers from each rootstock below the bud union is also essential and should be attended to regularly along with thinning of the shoots for better penetration of sunlight and aeration. The best time for pruning in bearing trees is after the harvesting during dry period ( June –September).

1.5. Irrigation

Citrus trees require more water because sap circulation never entirely ceases and transpiration takes place throughout the year. Being evergreen plant, Citrus requires good amount of water and water deficiency moisture stress at critical periods reduces fruit size and quality. Thus, moisture stress during the period of growth, flowering and fruit development should always be avoided.

During the first 6 months the trees should be irrigated twice a week and thereafter every 7 days. In young plants up to the age of 8-year, the irrigation should be given through basin system of irrigation. Drip irrigation system is gaining popularity.

A grown up citrus tree needs about 25–20 irrigations in a year, amounting about 1,325mm of water. Citrus plants have highest demand of water during fruit development. It is advisable to irrigate the orchard after the fruits have attained pea size. Moisture stress during tree flowering could result in excessive drop of flowers and fruitlets, and the resulting crop will be small. A serious drought followed by good rains could produce out-of-season flowering and fruit setting.

1.6.  Fertilization

Fertilizer requirement of the plants is influenced by various factors like age of the plant, root-stock used, soil and climate along with the crop load in bearing trees. No uniform fertilizer recommendation can be made for all citrus cultivars in different agro-climatic regions. The fertilizer schedule commonly adopted is given below.

Table. Citrus nutrient recommendation per tree/year (g)

Table. Citrus Fertilizer recommendation  per tree/year (g)

The fertilizers should be applied in a ring from below the canopy of the trees depending on age. For a mature tree, fertilizer is applied in a 30–40cm wide ring made at a radial distance of 100–200cm from the trunk as maximum feeder roots are located in the space below the tree canopy.

Though the requirement of major elements is by and large met by supplementing N, P, K fertilizers, farmers usually forget to apply micronutrients, the most essential part of citrus nutrition. Further, deficiency symptoms of Mn, Fe and Zn resemble very closely, making it difficult to judge which nutrient is really deficient.

It is often necessary to apply micronutrients. These elements are dissolved in water and applied as a spray onto the tree. Deficiencies of zinc, copper and manganese often occur and may be applied in 10 L water at the following concentrations:

• 15 g zinc oxide

• 20 g copper oxychloride

• 20 g manganese sulphate.

The micronutrient solutions should be sprayed when the leaves are actively growing. A boron deficiency can be rectified by spreading 20 g borax per large tree under the canopy.

1.7. Managing alternate bearing

Certain citrus types such as oranges or some mandarins have a tendency to have a year with heavy fruit production followed by a year with sparse production. This is called alternate bearing. You can reduce the potential of a tree to alternate bear by reducing the fruit load on a heavy fruit set year by thinning out some of the fruit.  Pruning the tree will also help to offset alternate bearing. Also, fertilize less in light years and more in heavy years so that the trees needs are met according to the demands of the fruit load. Lastly, do not allow the old fruit to stay on the tree longer than necessary. Despite using these strategies, some varieties will just alternate bear.

1.8. Management of fruit drop

Some fruit drop is natural. Excessive drop may be due to drought stress, sudden high temperatures, low humidity, or nitrogen deficiency.

Heavy pruning, thrips, mites, or spray injury can also cause fruit to drop. Keep trees in good health to minimize fruit drop.

Fruit drop is a self-regulating mechanism in citrus trees. Too much fruit set will cause small fruit size. Additionally, excessive fruit set can also be damaging to trees.

Management of pests and diseases: Orange

1.1. Alternaria Brown Spot (Alternaria alternata or A. citri)

Conidia are released by rain events or sudden changes in relative humidity. Optimum temperatures for diseases development are 23-27°C. Plants can get infection between 17-32°C. Infection can occur with as little as 4-6 h of leaf wetness but disease severity increases with leaf wetness.

Management:

• Disease-free nursery trees;
• Careful choice of planting site;
• Air drainage is important;
• Wider spacing;
• No vigorous rootstocks;
• No over-fertilization or over-watering;
• No overhead irrigation.
• Chemical control: Copper based fungicides. Maintain protective coating.

1.2. Melanose (Diaporthe citri)

The disease causes lesions on fruit and leaves. All citrus are susceptible but grapefruit and lemons are the most susceptible. Optimum temperature for the disease development was determined to be 24-28 °C.

Management:

•  Remove dead wood from canopy.
• Copper based fungicides.

• Copper to be applied every 3 weeks until fruit are fully developped.

1.3. Pseudocercospora Fruit and Leaf Spots
 (Pseudocercospora angolensis; Syn.: Phaeoramularia angolensis)

This is a quarantine disease affecting all Citrus but the most susceptible are grapefruit, oranges and mandarin; while the less susceptible is lemon. Yield loss due to this disease ranges between 50-100%.

Young leaves are highly susceptible to infection from lesions older tissues. Young fruit up to golf ball size are also highly susceptible.

The disease spread is so far restricted to humid tropics of Africa between 800-1500 m and is favoured by prolonged wet weather followed by dry periods with temperatures between 22-26°C. Leaves are the main source of inoculum. The disease is long distance spread by windborne conidia. Infected planting material may also contribute to long distance spread. Within the orchard, spread is by splash dispersed conidia.

Symptoms:

Fruit lesions are circular to irregularly shaped. Young fruit has nipple‐like lesions with yellow halo. And can become mummified. Mature fruit lesions are dark brown to black and generally flat or sunken with a yellow halo.

Leaf symptoms are circular to irregularly shaped lesions that can coalesce. Leaf lesions with brown or grayish center surrounded by a yellow halo. Young  flush can be killed and leaf drop can occur.

This is a quarantine disease affecting all Citrus but the most susceptible are grapefruit, oranges and mandarin; while the less susceptible is lemon. Uield loss due to this disease ranges between 50-100% .

Management:

• Inoculum control via collecting and destroying all fallen fruits and leaves in affected orchards;
• Plant windbreaks around the citrus orchards. Wind is the primary dispersal agent spores;
• Discouraging inter-planting in affected orchards with mature producing trees;
• Prevents creation of a microclimate of relatively cool temperatures and high RH;
• Judicious pruning of shoots to allow light penetration and aeration within the tree canopy;
• Fungicides: Alternate Benomyl and copper sprays every 2 weeks from a week following the onset of rains.

1.4. Citrus greening

Citrus greening disease is a major cause of crop and tree loss in many parts of Asia and Africa. Before it was identified as one disease, it became known by various names: yellow shoot (huanglungbin) in China; likubin (decline)in Taiwan;  dieback in India; leaf mottle in the Philippines;  vein phloem degeneration in Indonesia; and Yellow branch, blotchy-mottle, or greening in South Africa.  As it became clear that all these were similar diseases the name “greening” was widely adopted.

Nature of the causal agent:

The demonstrations that greening is a graft- and insect-transmissible disease led to the conclusion that a virus was responsible. In China some researchers believed tristeza virus to be the cause. In South Africa it was shown that tristeza and greening could readily be distinguished since the aphid Toxoptera citricidus transmitted tristeza but not greening, and psylla vice versa. Other researchers suggested that it should be classified as a true bacterium.

Citrus greening is caused by phloem-limited bacteria. The African form of the disease is heat sensitive, and the Asian one is not. The bacteria are transmitted by insect vectors and by grafting.

Symptoms:

• Citrus greening disease is characterized by leaf symptoms reminiscent of severe nutritional deficiencies, yellow shoots , twig dieback, tree decline, and reduced fruit size and quality. Symptoms resembling zinc deficiency occur on younger leaves, and older leaves develop a characteristic mottle.
• Fruit yield is severely reduced, and what little fruit is produced is greatly reduced in quality, poorly colored (hence the name greening), and have a bitter, sour flavour.
• Root system is poorly developed with relatively few fibrous roots. New root growth is suppressed and the roots often start decaying from the rootlets.

Losses due to greening are not easy to assess. Sometimes only sectors of a tree are affected and losses are small, but in other cases the entire tree is infected and crop loss is total.

Management:

To date, there is nowhere in the world where citrus greening disease occurs that it is under completely successful management. In every place where the disease occurs, life expectancy of citrus trees is vastly reduced and production losses are significant.

• The most successful management efforts combine production of clean stock with psyllid control and inoculum suppression once plantations are established.
• Psyllids must be controlled both within plantations and on any alternative host plants.
• Inoculum suppression involves removal or severe pruning of any affected plantation trees several times each year. Non-commercial citrus and any alternative hosts of the pathogens may also need to be removed.

1.5. Aphids: Black citrus aphid (Toxoptera aurantii), Cotton or melon aphid (Aphis gossypii), Spirea aphid: Aphis spiraecola

Aphids feed on buds and on the underside of leaves , causing leaves to curl toward the stem. Spirea aphid, black aphid and cotton aphid can all transmit citrus tristeza virus.  Insecticide applications for aphids are not recommended because it is difficult to prevent transmission of citrus tristeza virus by controlling aphids with insecticides unless an area wide treatment program is conducted.

Management:

• Natural enemies normally control aphid populations and an insecticide application is rarely warranted.
• Biological Control: A number of coccinellid and syrphid predators, parasites, and fungal diseases usually keep aphid populations below damaging levels.
• Treatment Decisions: On newly established trees and on new growth flushes on mature trees, it is not uncommon for aphids to cause curling of leaves and produce honeydew.
• Treatment is usually not warranted because citrus can tolerate extensive leaf curling without yield effects. Pesticide applications are reserved for special situations such as area wide treatment programs.

1.6. Citrus mealybugs (Planococcus citri)

The citrus mealybug is a sporadic, and extremely damaging and difficult to control pest of citrus. They prefer humid conditions. In citrus, mealybugs spread by crawling from tree to tree, wind, on bird’s feet, machinery, and labor crews.

On hatching, the nymphs are light yellow, but they soon excrete a waxy covering. There are 2-3 generations per year.

Damage:

• Mealy bugs suck plant sap reducing vigour and causing fruit to drop.
• They also contaminate bunches of citrus by their presence or by the sooty mould growing on honeydew.

Management:

• Pruning & hedging. Hedging trees to prevent touching between trees will help prevent within grove spread of infestations. Additionally, pruning will aid in opening up the canopy to maximize spray penetration and coverage.
• Equipment Sanitation. Thorough cleaning of equipment and harvest materials will help prevent the spread of mealybug from an infested grove to others.
• Ants must be controlled to allow natural enemies to do their job. Sowing vetch (Vicia sp) as an intercrop will attract ants away from the mealybugs.
• Natural conytrol: Mealybugs have a lot of natural enemies: parasites and predators. One of the best known is Cryptolaemus montrouzieri, the Mealybug Destroyer, which is a type of ladybird. Its larva is similar to a mealybug but is larger and has long waxy filaments. It can be imported and introduced.
• Chemical: Treatments are most effective against ‘crawlers’. No treatments are effective against mealybugs in closed fruit bunches. Imidacloprid is highly systemic and can be applied to the soil before irrigation at bloom.

Harvesting:Orange

Mature fruits are picked up in 2 – 3 cycles in a year. Being to a non-climacteric fruit, there is no improvement in colour, taste and flavour after harvesting. Therefore, fruits should be harvested when they are fully ripe and attain proper size, attractive colour and acceptable sugar: acid blend.

All fruits must be harvested in a season. Leaving fruits on the tree after maturing may contribute to a smaller crop and perhaps, more fruit drop for the next crop.

The economic life of orange plantation is 25-30 years. The yield  commences from 3^rd/4^th year with 15 to 20- fruits per tree and stabilizes around the 8^th year. Average production is about 175-250 fruits per tree after stabilization.

Post harvest Management : Orange

Oranges will last up to 2 weeks safely under refrigeration or out at room temperature. Do not stress over where you keep your oranges, the only key is to keep them in an open place. By covering oranges, you are eliminating air flow and enabling moisture to build up which is exactly what mold needs to grow.

Oranges are eaten fresh or juiced. Juice and/or zest can be kept longer but should be refrigerated. You can even freeze orange juice in a ice cube tray for easy smoothie work.