Citrus is a genus of flowering trees and shrubs in the family Rutaceae, grown for their fruits, which are eaten fresh, pressed for juice, or preserved in marmalades and pickles.
These plants are large shrubs or small to moderate-sized trees, reaching 5–15 m tall, with spiny shoots and alternately arranged evergreen leaves.
The flowers are solitary or in small corymbs, each about 2–4 cm diameter, with four to five white petals and numerous stamens. They are oftenly very strongly scented.
The fruits are notable for their fragrance, partly due to flavonoids and limonoids which in turn are terpenes contained in the rind, and most are juice-laden. The juice contains a high quantity of citric acid giving them their characteristic sharp flavour.
They are good sources of vitamin C and flavonoids. The content of vitamin C in the fruit however depends on the species, variety and mode of cultivation.
Citrus trees are unique compared to other fruit trees as they never go dormant and their fruits do not improve in quality or taste once it has been picked. In fact, the longer the fruits stay on the tree, the sweeter they become.
Citrus fruits are produced all over the world.
TYPES OF CITRUS CROPS
- Sour & sweet oranges
- Tangerines/ Mandarins
The growth, development and production of citrus plant depends on the physical characteristics of the soil such as drainage, water-holding capacity, structure, soil depth, and the degree to which water can infiltrate the soil, among others. These characteristics however differ in the various soil types.
Citrus can be grown in a wide range of soil types. However, for best results, they should be grown in well-drained soils, which are fertile, well-aerated and with a pH of between 6-6.5.
Citrus trees should be planted in a sunny and wind-protected area, and in frost-free regions because they cannot tolerate severe frosts.
They can tolerate high temperatures provided the trees are well supplied with soil moisture.
PLANTING & CULTURAL PRACTICES
The trees are grown from either grafting or budding. The commonly used are grafts.
Grafts are got from joining the top of the tree, (scion) with a different variety to the roots (rootstock) of the tree. This growing process begins with propagating new citrus trees by planting seeds for the rootstocks.
- Land preparation. This is made easier and effective by use of CLAMPDOWN 480SL 200ml/20l, a non-selective herbicide which kills all types of weeds.
- Prepare planting holes about 0.5 x 0.5 x 0.5M
- Fill the holes with topsoil mixed with manure and DAP. In order to improve on nutrients uptake by the young plants as well as stimulating growth, it is advisable to incorporate manure and DAP with HUMIPOWER at the rate of 1ton manure and 50kg fertilizer in 1kg Humipower each.
- Water the holes unless the soil is wet enough.
- Plant the grafts in the holes, to the same depth as they were in the nursery. The bud union should be about 300mm above the ground.
Spacing– standard-sized citrus trees should be spaced 12-25 feet apart while dwarf citrus trees should be set 6-10 feet apart. The exact distance however depends on the variety. For instance, the bigger the fruit, the farther the distance.
Irrigation-citrus trees require regular water supply. Since rainfall is often poorly distributed and in most cases deficient, it is necessary to supplement moisture by irrigation to ensure that moisture stress do not suppress growth and production.
Newly planted grafts should be watered daily until they establish.
Pruning– dead wood must be removed regularly. When the trees become too big and start growing into one another, pruning is also recommended.
Branches touching the ground hamper the removal of fruit lying underneath the tree, impede irrigation and promote ant infestation of the trees. They should also be removed.
Weeding– it is very important to keep the area under the canopy free from weeds. This is because the weeds compete for growth factors like nutrients and water and harbour pathogens.
CLAMPDOWN 480SL 200ml/20l is a non-selective herbicide which controls all types of weeds in the garden.
PESTS & DISEASE CONTROL
False coddling moth– the larvae burrow into the rind of the fruit and a discoloration appears at the point of entrance. While inside they feed on the pulp, causing premature ripening and fruit drop. Young larvae feed on the outer portion while older ones move further into the interior of the fruit. Larvae prefer the navel end of citrus but can burrow anywhere on the fruit leaving excrement around the openings.
Spray KINGCODE ELITE 50EC 10ml/20l or LEGACY 50EC 15ml/20l or SINOPHATE 750SP 20g/20l
Aphids– under favorable conditions the aphid population can grow very rapidly and cause serious damage to a citrus tree during the growing season.
They attack the tree by sucking the sap out of the leaves. The symptoms are very visible on the leaves in the form of multiple puckered marks, yellowing and the twisting of the leaves, which gives the appearance of deformed leaves. As the severity of the aphid infestation increases, leaf drop and twig and branch die back can be seen.
During an aphid infestation, the leaves appear to be dripping sap from the underside of the leaves. This is an excretion from the aphids and is called honeydew. It oftenly drips onto other leaves, other plants and on to the ground. The honeydew attracts ants, which feed on it. In most cases the ants are only symptoms of the honeydew and are not actually attacking or hurting the tree. It also encourages the development of sooty molds.
Spray KINGCODE ELITE 50EC 10ml/20l or LEXUS 247SC 8ml/20l or PRESENTO 200SP 5g/20l
Orange dog caterpillar– this is a large caterpillar about 1.5-2 inches long, brown in color.
The caterpillar attacks citrus trees by eating the leaves and they can very rapidly defoliate an entire tree in only a few days.
Spray KINGCODE ELITE 50EC 10ml/20l or BACIGUARD 16WDG 15g/20l or SINOPHATE 750SP 20g/20l
Citrus whiteflies– these are tiny white winged insect which are most commonly found feeding on the underside of the tree’s leaves. When the branches are shaken, they rapidly take flight and can be seen fluttering around the tree.
They feed by sucking the sap from the leaves, causing the leaves to curl and become malformed. Whiteflies excrete honeydew, because they are not able to metabolize all of the sugars contained in the leaf sap. The honeydew attracts insects like ants as well as facilitating for the growth of sooty mold.
Spray TAURUS 500SP 10g/20l or LEXUS 247SC 8ml/20l or PRESENTO 200SP 5g/20l
Fruit fly– adults deposit their eggs under the skin of mature and ripening fruit. The eggs hatch into maggots which feed on the flesh of the fruit causing it to rot. This may cause fruit fall.
Spray PENTAGON 50EC 10ml/20l or LEXUS 247SC 8ml/20l
Citrus leafminer– the larva feeds on young foliage within the leaves, creating distinctive silvery tunnels or mines and damage is usually worst when there is a new flushing growth. Heavy infestation may lead to defoliation.
Spray ALONZE 50EC 5ml/20l or SINOPHATE 750SP 20g/20l or AMAZING TOP 100WDG 5g/20l
Brown soft scale– this is a common problem on citrus trees. These are small, non-mobile insects that attach themselves to the wood, foliage and sometimes the fruit. When adult scale is attached to the tree, it oftenly appears as crusty or waxy bumps on the tree, and is mistaken for part of the tree’s own growth.
The scales suck sap from the tree causing the leaves to turn yellow and drop. Severe infestation can cause defoliation.
A sticky substance (honeydew) can be found near the scale or on the leaves, which attracts ants and facilitates for sooty mold development.
Spray LOYALTY 700WDG 5g/20l or EMERALD 200SL 10ml/20l or LEXUS 247SC 8ml/20l
Citrus thrips– they are tiny orange or pale yellow insects that attack citrus, mainly the young leaves and juvenile fruit and feed on the tree’s sap.
When a tree is infected with these pests, the most visible signs and symptoms of the infestation are shriveled leaf buds and leaves that are curled, distorted and often a silvery grey color. The fruits may be scabbed, streaked or develop a silvery color.
Spray ALONZE 50EC 5ml/20l or PROFILE 440EC 30ml/20l or DEFENDER 25EC 40ml/20l
Citrus bud mite– this mite is exceptionally small and hides in the flower and axillary buds. It causes malformed growth points, flowers and fruit and also peculiarly shaped leaves. The growth of young trees is seriously affected and yields can be reduced dramatically.
Spray ALONZE 50EC 5ml/20l or BAZOOKA 18EC 10ml/20l
Citrus canker– this is a highly contagious bacterial infection of citrus trees which causes yellow halo-like lesions or scabs on the fruit, leaves and twigs of citrus trees. Severe infections can lead to leaf loss, blemished fruit, fruit drop and die back.
The canker bacterium spreads easily and quickly on air currents, insects, and birds and on humans by means of clothing and infected implements.
Spray GREENCOP 500WP 50g/20l or TRINITY GOLD 425WP 50g/20l or COLONIZER 440wp 50g/20l
These are Copper-based fungicides which suppress and prevent bacterial infections.
Sooty mold– this is a fungus, which causes the blackening of the leaves and fruits of citrus trees. The mold forms as a result of honeydew secretions from insects such as whiteflies, aphids and mealybugs. Insect control is the most effective way to prevent the incidence of this disease.
Spraying JAMBO CLEAN 100ml/20l cleanses the sooty mold.
Greasy spot– it is a fungal disease of citruses, whose signs and symptoms of infection include yellowish-brownish blister spots on leaves, often on the underside of the leaf. As the disease develops, the spots develop into oily looking blisters. These greasy spots can cause significant leaf loss and can also infest citrus, particularly grapefruit, rind.
Spray ABSOLUTE 375SC 10ml/20l or RANSOM 600WP 15g/20l or EXEMPO CURVE 250SC 15ml/20l
Anthracnose– 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.
Spray RANSOM 600WP 15g/20l or DUCASSE 250EC20ml/20l or EXEMPO CURVE 250SC 15ml/20l
Bacterial blast– infection starts as black lesions in the leaf petiole and progresses into leaf axils. Leaf blades curl, dry, and drop prematurely, often leaving petioles remaining stuck on the twig. When twig lesion girdles the stem, twig and branch dieback can result.
Spray Copper-based fungicides; GREENCOP 500WP 50g/20l or COLONIZER 440WP 50g/20l or TRINITY GOLD 425WP 50g/20l
Root Rot/ Brown Rot/Collar rot– this is a tree disease caused by the soil-inhabiting fungus from the Phytophthora sp. Symptoms of infection are dark brownish patches of harden bark on the trunk of the tree. It is common for ooze to seep from the dark brown infected area. As the disease 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. This happens as it is splashed up on the tree by rain or irrigation spraying.
Drench soil with GEARLOCK TURBO 250WP 50g/20l or PYRAMID 700WP 100g/20l or CHANCETYL ELITE 800WDG 100g/20l
Citrus greening– this is caused by a bacterium spread by aphid-like psyllids. Symptoms due to infection include yellowing in just one section of a tree, stunted growth, leaf and fruit drop, twig dieback and fruits are lopsided, small and bitter-tasting.
Spray Copper-based fungicides; GREENCOP 500WP 50g/20l or COLONIZER 440WP 50g/20l or TRINITY GOLD 425WP 50g/20l
Powdery mildew– white ‘powdery’ spores develop mostly on the upper leaf surface, causing them to turn pale whitish to grey-green. 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.
Spray RANSOM 600WP 15g/20l or DOMAIN 250EC 10ml/20l or DUCASSE 250EC 20ml/20l
Citrus gummosis– the trees become infected when fungal spores on the ground splash onto the trunk. If the trunk remains wet for many hours, whether from rain droplets or irrigation, infection takes place. The fungus attacks and kills the bark but does not penetrate into the wood. Once the infection spreads and kills more than a third of the bark tissue around the trunk, the tree either dies or produces very poorly. Such trees are sparsely foliated with much twig dieback.
Trees produce an amber color gum as a defense against the invasion. The gum exudes from the point of infection and in a rainy climate, the globes of gum readily dissolve in the rain. Due to temperature fluctuations, the fungus may die out on its own and when this happens, the infected bark dries up and cracks. New bark eventually begins to grow around the wound.
The disease is best controlled through prevention, using systemic fungicides like GEARLOCK TURBO 250WP 25g/20l or CHANCETYL ELITE 800WDG 50g/20l or TRINITY GOLD 425WP 50g/20l or COLONIZER 440WP 50g/20l
NUTRITION & NUTRITIONAL DEFICIENCIES
In order to remain healthy and produce optimally, the plants require sufficient nutrients, both macro and micronutrients.
Nutrients that are needed in relatively large amounts are called the macronutrients.
Basal and foliar fertilizers should therefore be applied in order to ensure effective nutrient supply to the plants.
Basal fertilizers are absorbed by the plants through the roots and include DAP, CAN, NPK, UREA, among others. They should be mixed with HUMIPOWER at the rate of 50:1, which helps in improving nutrient uptake by the plants as well stimulating growth.
Foliar fertilizers are absorbed by the plants through the foliage and they supply both macro and micro nutrient elements. They include OPTIMIZER, DIMIPHITE, ZINC GOLD, LAVENDER, GOLDCHANCE RANGE, LEGENDARY, PORTEGE GOLD, VITABOR GOLD, among others.
Application of these fertilizers prevents nutritional deficiencies.
A nutrient deficiency may express itself on the entire tree level causing twig die-back, long thin branches, yellowing, and reduced or abnormal growth.
Nutrient deficiencies can alter fruit characteristics such as shape, hardness, peel thickness, and peel texture and may manifest on leaves resulting in chlorosis, enlarged or shrunken leaves, raised veins, unusual leaf patterns and changes in leaf coloration.
Deficiency is expressed by light green to yellow foliage over the entire tree in the absence of any distinctive leaf patterns.
With mild deficiency, foliage is light green progressing to yellow as conditions intensify. New growth usually emerges pale green in color, but darkens as foliage expands and hardens.
With yellow vein chlorosis, the midribs and lateral veins turn yellow while the rest of the leaf remains a normal green color. This chlorosis is frequently attributed to girdling of individual branches or the tree trunk.
Nitrogen deficiency is also associated with senescing foliage which can develop a yellow-bronze appearance prior to leaf abscission and limits tree growth and fruit production.
Correction; use GOLDCHANCE SUPER GROWTH or LAVENDER
Deficiency symptoms begin at the mature/older leaves which partly turn yellow and in severe cases small brownish to bronze freckles develop, spreading over the leaf blade.
Fruits are rather coarse with thick rinds and have lower juice content which is higher in acid. Although rarely observed, foliage may exhibit a bronze appearance.
Correction; use GOLDCHANCE SUPER START or LAVENDER or LEGENDARY or DIMIPHITE or GREENPHITE
The leaf margins of older leaves turn pale yellow or sometimes bronze. As deficiency progresses, chlorosis spreads over the entire leaves.
Fruit are smaller, have smoother, thinner rinds and may be subject to splitting and/or drop.
Correction; use GOLDCHANCE SUPER FLOWERS & FRUITS or DIMIPHITE or GREENPHITE or LEGENDARY
The initial stages of deficiency appear as small blotches of yellow between green veins on the leaf, and as severity increases, leaves may become increasingly yellow except for the green veinal areas. Leaves also become small with narrow pointed tips on terminal growth.
Correction; use ZINC GOLD
Mild copper deficiency is usually associated with large, dark green leaves on long soft angular shoots. Young shoots may develop into branches which appear curved or “S-shaped,”. Twigs can develop blister-like pockets of clear gum at nodes, and as they mature, reddish brown eruptions may occur in the outer portion of the wood.
Severely affected twigs commonly die back from the tip with new growth appearing as multiple buds.
Necrotic-corky areas on the fruit surface may sometimes occur in severely deficient trees.
Correction; use BIO DISTINCTION or COLISEUM
In mild cases of deficiency, leaf veins are slightly darker green than interveinal areas with symptoms appearing first on new foliage. In severe cases, interveinal areas become increasingly yellow with entire area eventually becoming ivory in color with emerging foliage, which is smaller.
Trees may become partially defoliated with eventual twig and canopy dieback.
Correction; use PORTEGE GOLD FE 6% or EURO GOLD PLUS or MICRO GOLD 11% DTPA
Deficiency causes death of the growing points, the tree loses its apical dominance and develops several shoots.
Fruit symptoms develop darkish-colored spots in the white albedo of fruit and sometimes in the central core. The fruit may be somewhat misshapen with a lumpy surface.
Boron can impact fruit quality and should therefore not be allowed to occur.
Correction; use VITABOR GOLD
- Whenever doing foliar sprays, it is advisable to mix the product (insecticide, fungicide, foliar fertilizer or herbicide) with INTEGRA 3ml/20l. This is a sticker, spreader, wetter and penetrant, which improves the efficacy of the respective product.
- Alternation of various chemicals (especially fungicides and insecticides) throughout a crop’s season help in preventing resistance build-up by the pest, which could happen if only a single chemical was used.
- Timely application of products (fertilizers, insecticides, fungicides & herbicides) is very crucial.
Maturity, Harvesting & Post-Harvest Handling
A mature fruit is one that has completed its growth phase.
Depending on the ecological conditions, citrus fruits may take 6-8 months.
Ripening is the changes that occur within the fruit after it is mature to the beginning of decay. These changes usually involve starches converting to sugars, a decrease in acids and a softening and change in the fruit’s colour.
Harvesting of the fruits is done by cutting them off with pruning shears or by pulling the fruits stalk from the tree.
Once the fruits are separated from the tree, they do not increase in sweetness or continue to ripen. Therefore, they should not be picked too early.
Colour cannot be used as an indicator of ripeness because sometimes the rinds turn orange long before the fruits are ready to eat, e.g. in oranges. The best indicator of ripeness is taste.
Harvested fruits can be stored for several weeks at cool temperatures.