TANGERINES GROWING MANUAL AND PESTS AND DISEASES AFFECTING TANGERINE IN KENYA

Tangerine is a citrus fruit that is very sweet and delicious with an  orange skin which can be easily pulled away from the flesh. The fruits are the most popular variety of the citrus fruits. They do well both in outdoor and indoor settings. Most of the tangerine fruits are seeded. These fruits have the shortest lifespan among all citrus fruits. A tree can produce fruit on its own without the need for cross pollination. However,   planting more than one tangerine cultivar in an area can increase the yield of tangerines on all the trees. Among the most popular cultivars include Clementine, Dancy, and Sunburst.

IDEAL ECOLOGICAL CONDITIONS FOR TANGERINE CULTIVATION

Rainfall

Annual rainfall of at least 1000mm is ideal which should be well distributed throughout the year.

Temperatures

Ideal temperatures range from 20 to 34 degrees Celsius. There is a risk of flowers dropping prematurely in areas that experience very high temperatures. Some varieties are cold-tolerant while some are heat-tolerant.

Soil

They do well in wide range of soil types. The soil should be fertile, deep, light, loamy with a  pH range 5.0- 7.0

SUN

The yield is great if the trees get full sun. The more hours of sun each day, the heavier your flowering and fruiting. However, some trees do well in partial shade.

Altitude

Tangerines grow in altitudes of up to 2100 m above sea level.

PLANTING AND MAINTENANCE OF TANGERINES

Propagation

Propagation is done by both seeds and via grafting. Grafting is much preferred than seeds. Tangerines grown from seeds give lower yields than those grown via grafting. Tangerines grown via grafting take few years to mature and are more resistant to diseases than the latter. Grafting is done by joining the top of the tree (scion) with a different variety to the roots (rootstock) of the tree.

Land preparation and Planting

Proper site selection is the key to successful tangerine growing. Therefore ensure you choose a site that meets the conditions necessary for growing of these fruits, giving special considerations to soil conditions and sunlight.  Clear the land and remove weeds. Prepare planting holes size 60cm×60cm deep. A tree spacing of around 6m by 6m is preferable for proper aeration and sunlight penetration. An acre can occupy at least 200 seedlings. Ensure you have a water backup plan. During planting, separate top soil from subsoil and then mix with about 20kg of well –rotted farm manure in each hole. Fill the hole with manure and the top soil mixture and plant the graft to the same depth as they were originally in the nursery then cover the hole with the remainder of the top soil mixed with compost. Ensure you water the holes unless the soil is wet enough. The bud union should be about 300mm above the ground. Apply grass mulch around the plant to conserve water.

Watering

The tree is capable of withstanding long periods of drought, nevertheless irrigation is important especially in the initial stages of growth and during and after flowering to ensure sufficient water for fruit set and growth. Watering should be done at least 2 times a day in the initial stages of planting and be consistent when watering since fluctuating amounts of moisture will cause the tangerines to split Remember that over-watering can kill the tree by drowning the roots or promoting rot. Poor watering leads to small non- succulent fruits. Drip irrigation system is ideal for watering the trees. Another option is to dig a ditch around the tree, at the drip line, and fill it with water 7-10 days, depending on the soil and climate conditions.

Fertilizer application

Well-rotted farmyard manure or composed can be used to improve soil organic matter. Feeding tangerine trees is important if you want to have a healthy tree and get a good crop of fruit each year. Oxfarm Organic Ltd recommends that you apply a fertilizer designed especially for citrus trees, as the trees are heavy users of zinc, nitrogen and iron. Follow label directions to determine the correct amount for your tree, and divide the yearly dose into thirds, applying the first feeding in the spring, just before the tree blooms; the next dose two months later; and the final feeding a month after that. Don’t feed the tree in late summer, typically after July, as you may end up stimulating new growth that will be too tender to survive the winter.

Mulching

Organic mulch around the trees is recommended to conserve moisture around the plant. Mulching also greatly contributes in weed control.

Pruning

Although these trees do not need regular pruning, pruning is essential to maintain a well- structured tree. The height of branching should be allowed at 1m high. Remove dead and broken branches from excessive weight of fruit. Maintain a single stem and choose 3 or 4 main branches to form the framework of the tree. Ensure that the pruning shears is clean and sharp.

Thinning

Remove some fruits if the tree is overloaded. Remove all the fruits from trees that are two years old or less, allowing the trees time to become well-established before producing fruit.

Maturity, harvesting and yield

Grafted tangerine seedlings take approximately 2-3 years to start fruiting after transplanting. Those grown from seed require up to 5 years before producing flowers and fruit. However, the number of days from flowering is not a reliable index of harvest maturity. Additionally, the fruit size is not always a confirmation for maturity. The peel color is a good test for maturity. Tangerines are mature and ready for harvest when most of the peel turns yellow in color.

The fruits are harvested by hand using clippers to detach the fruit .Never pull off the fruit from the as part of the skin tissue might remain attached to the stem, creating a small opening in the peel surface. This is commonly known as ‘plugging’ and it results in an open wound in the skin through which disease causing micro-organisms penetrates.

A mature single tree produces up to 500 fruits per season by year 5. The current price of each fruit is Ksh 20. This means you can get Sh 10000 per tree in each harvest season. In Kenya there are two harvest seasons i.e June- July and December –January. Yield can be up to 300kgs per tree.

Cleaning, grading, and packing of the fruits should be done soon after harvesting. The ideal storage temperature for tangerines is 4 degrees Celsius and at this temperature the fruit will have a storage life of 4 to 6 weeks.

PESTS AND DISEASES OF TANGERINES

PESTS

  • Whiteflies

These are tiny white-winged insects found mostly on the underside of the leaves. When the branches are shaken, they rapidly take flight and can be seen fluttering around the tree. They suck sap from the leaves causing the leaves to curl and become malformed.  They excrete honeydew thus promote growth of sooty mold. These insects are kept under control by their natural enemies such as the parasitic wasps. Use of pesticides to control them should be avoided since it may kill these natural predators.

  • Fruit fly

The adults deposit their eggs under the skin of the fruit. The eggs then hatch into maggots which feed on the flesh of the ripening fruit causing it to rot. This may cause fruit fall. Fruit flies are controlled by orchard sanitation and application of baits.

  • Aphids

Aphids damage the trees especially during the young ones during the growing season. They suck sap from the leaves which results to yellowing of the leaves and puckered marks on the leaves. In severe infestations, they cause defoliation and branch die backs can be seen. These insects extract honeydew which attracts ants and leads to development of sooty molds. Aphids are frequently controlled by natural enemies such as ladybird beetles, lacewings, hoverflies and parasitic wasps. Insecticides should only be applied only when there is heavy infestation

  • False coddling moth

These cause premature ripening and fruit drop. The initial symptom on the fruit is a yellowish round spot with a tiny dark center where the insect entered the fruit. In a later stage brown patches appear on the skin, usually with a hole in the center. Maintain proper orchard sanitation. Infested fruits should be removed immediately disposed of.

  • Scales

These are white or brown insects that excrete honeydew causing growth of sooty mould that destroy the leaves and fruits. The fruits are loose market value. Biological control measures should be adopted such as using natural enemies such as the parasitic wasps and other predators. In cases of heavy infestation, necessary pesticides should be used.

  • Thrips

These are tiny orange insects that affect the young leaves and fruits by sacking sap from these parts. They cause curling of leaves which are distorted and discoursed fruits

 

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DISEASES

·         Greasy Spot

Caused by the fungus Mycosphaerella citri, greasy spot spores germinate on the undersides of leaves. This infection causes yellow spots on leaves. These greasy spots also appear on upper leaf surfaces as infection progresses. As the disease advances, the spots develop into oily looking blisters. These greasy spots can cause leaf defoliation. To control greasy spot, apply copper fungicide plus oil when symptoms first appear, and repeat applications in 7 to 10 day intervals as needed, thoroughly covering the undersides of the leaves.

  • Citrus canker

 This is a bacterial infection which causes yellow lesions on the fruits, leaves and twigs of the trees. Severe infections can lead to leaf defoliation, blemished fruit, fruit drop and die backs. This infection is spread by insects and birds and on humans by means of clothing and infected implements. Observe farm hygiene in all operations. To suppress these infections, copper based fungicides are used.

  • Root Rot

The disease is characterized by dark brownish patches of harden bark on the trunk of the tree. As the infection advances, the bark dries cracks and dies and the infected area is then left as a dark sunken canker. The disease can also cause browning and decaying on the fruit and yellowing and die-back on the foliage.

  • Alternaria Brown Spot

This infection causes brown spots surrounded by yellow borders on the leaves. Sunken dark spots surrounded by a yellow halo may also appear on the fruit. The spots on infected fruit that remains on the tree become corky. This disease can cause serious leaf and fruit defoliation. Copper- based fungicides can be used to control this disease.

  • Brown Rot

This is a serious post-harvest disease of tangerines during extended periods of rainy weather. Spores of the fungus are produced in the soil and splashed onto low-hanging fruit in the tree canopy. Additional spores may be produced on these infected fruit, and disseminated by water to other fruit in the tree. Spores germinate in free water on fruit surfaces and the fungus can penetrate the intact rind in a matter of a few hours. Symptoms first appear as a light brown discoloration of the fruit peel. The affected area is firm and leathery. White fungal growth appears on the fruit surface under humid conditions. Infected fruit have a characteristic pungent, rancid odor, which distinguishes this disease from other rots. Control of brown rot is obtained using a combination of field sanitation, disinfection of the harvest containers, wash water sanitation, and holding the fruit at 4 degrees Celsius.

  • Anthracnose

Anthracnose is caused by the fungus Collectotrichum gloeosporioides and usually appears on fruit previously injured or held for more than several weeks in storage. Symptoms appear as brown to black spots on the peel.  Under humid storage conditions, the fungal spores associated with the peel lesions are pink or salmon-colored, while under drier conditions they appear brown or black. Control of anthracnose is obtained by using timely pre-harvest fungicide applications to lower the inoculum level, avoiding injury to the fruit during harvest and handling, application of a postharvest fungicide application and holding the fruit at 4 degrees Celsius. This infection causes twig dieback, premature leaf drop, and dark staining on fruit can occur. Dying leaves and twigs become covered with dark fungal spores by which the pathogen spreads. It is characterized by brown to black sunken lesions on the infected part.

  • Powdery mildew

These white powdery spores develop mostly on the upper leaf surface, causing them to turn pale whitish to grey-green. The infection is mostly found in poorly drained areas. The ends of mildewed leaves can twist and curl upwards. Severe infection causes defoliation, withering of young shoots and diebacks. Fruits also develop whitish spores and may fall prematurely.

  •   Citrus Scab

Citrus scab causes corky growth to develop on the fruit and on leaves and shoots. Fruit lesions begin as pink to light brown pustules, and later resemble cracked warts, turning yellow-brown and then dark grey. The growths can become so numerous that the fruit is distorted. Control citrus scab with an application of copper –based fungicides.

  • Phomopsis Stem-end Rot

Caused by the fungus Phomopsis citri, this is a serious postharvest disease of tangerines grown in humid coastal production areas. Decay begins at the stem end of the fruit and spreads evenly down the peel. Eventually the rot will penetrate the rind and enter the juice sacs. The infected tissue shrinks and shows a clear line of separation between diseased and healthy rind tissue. The disease does not spread from decayed to healthy fruit in packed cartons. Control of stem-end rot is through pre-harvest fungicide sprays and storage of the fruit at 4 degrees Celsius.

If you are interested in establishing a tangerine Orchard we have made it very easy for you with only 20,000, you will only have to produce the land, we produce the seedlings and do the planting at your comfort. For those who are doing less than an acre we have certified seedlings at sh 150 each. At Oxfarm Organic Ltd, we have certified fruit seedlings in our nursery. In addition, we provide consultancy services on planting, management and marketing of the produce. For more information, visit our office in Nairobi (Hermes house opposite KTDA, Tom mboya) or Eldoret (opposite veecam house). Contact 0712075915/0783710808 www.oxfarmorganic.co.ke

 

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