Citrius

Propagation

• Although oranges can be grown from seed, budded or grafted (vegetative propagation), seedlings are preferred as planting materials.
• The budding on grafting union should be at least 30cm from the ground to avoid disease infection in the field.
• Propagation by seed takes a long time to produce fruits while vegetatively propagated seedlings take about 2 to 3 years.
• Vegetatively propagated materials can be obtained from government or private commercial nurseries.
• The land should be ploughed up to medium tilth and leveled if necessary.
• All perennial grasses such as couch grass should be cleared and burnt or sprayed beforehand using round-up or glyphogun.

Layout and Spacing

• It is important that the trees are aligned straight in the row and across rows.
• This necessitates proper layout of the field using pegs, string and tape measure.
• Dig holes 60x60x60cm with spacing of 3.3×3.3m.
• For each hole, the top soil should be separated from the red subsoil.
• It is advisable to plant at the beginning of the rains.
• Remove the polythene sleeves and place the seedlings in the center of the dug holes.
• Cover with soil up to the original level of the nursery sleeve but ensure that the graft joint/budded area is kept well above ground to avoid infection.
• A stake can be planted alongside the seedling to which the seedling is tied to keep it erect.
• Regular and adequate watering should be provided, all the way up to fruiting, depending on weather conditions.
• Then a cover a crop of beans or groundnuts should be planted during the first 3 years until the tree canopies have closed in.
• After the trees are fully grown, leave it as a mono-crop.
• Citrus is easily affected by root rot as other intercrops are being cultivated.
• Avoid planting the cover crop very close to the orange stalk.

Fertilizer

• DAP is normally applied to the soil before planting at a rate of 25g per hole.
• About 10-20kg of manure can also be added to the soil, mixed together and put back at planting.
• NPK fertilizer should be applied at the rate of half a kg per plant per year of growth, split into 2-3 applications per year i.e. apply about 250gm per rainy season.
• Increase the fertilizer by about 300gms NPK per year of growth up to year 10 when each tree gets 2.5 – 3 kg per year.
• Farmyard manure should be added at a rate of 2 Ddebes per tree per year.
• 75gm of Muriate of Potash applied per tree per year increases fruit sweetness.

Weed Control

• Weeds compete with young oranges.
• Weed before the weeds flower to prevent production of more seeds.
• Do not dig through as this will damage roots and cause root rot disease.
• Ring weed around the plants to get a weed free area for irrigation and application of manure and other fertilizers.
• Keep the fields weed free to avoid fruit and leaf spots.
• In case an herbicide is to be used, spray in the inter rows avoiding drift to the plants.
• In this case, there should be no intercrop.
• Where mulching materials, mulching is encouraged.

Training and/or Pruning

• Selectively timely pruning of orange tree branches results in higher yields of fruits.
• Pruning should ensure a round form which is umbrella shaped.
• Growing seedlings require air and sunshine.
• Abundant sunshine reduces insect pests and diseases and encourages good quality fruit growth.
• It is advisable to prune and manage the tree to about 3-4m in height.
• Trees should not be left to grow higher than 5-6m, this makes harvesting and pest and disease control difficult.

Harvesting

• Budded or grafted plants start producing fruits at about 2-3 years from planting.
• Full productivity is reached in about 10 years.
• Oranges stay on the tree from 6 to 9 months depending on the variety and climate conditions.
• Maturity is indicated by color change to slightly yellowish.
• Most trees bear twice a year.
• Harvest citrus fruits by clipping or pulling from the tree.
• Use of picking bags or baskets is recommended to collect the fruit and to prevent contact with the ground to reduce lowered quality.
• The average yield in Uganda is 10-12 tons/ha/year.
• With good management, one can get 40 tons/ha/year.
• One tree can produce 2 sacks (90-130kg)/tree per season.

Leaf miner

• These are very serious pests of oranges right from the nursery to the field.
• The adult moth deposits tiny eggs on the lower surface of the leaf.
• Upon hatching the larva enters the leaf where it remains until maturity.
• It then comes out of the leaf and forms a pupation cell by folding over a part of the leaf margin.
• The larvae sometimes mine in between the upper and lower surfaces,
• The serpentine mine is characteristic and conspicuous.
• As a result of the leaf mining, the lamina weakens and curls.

Control

The pest is resistant to most available insecticides. Bulldock alternated with Folimat can control leaf mines effectively.

Citrus psyllid

• It’s a common but minor pest of mature orange.
• It is more evident in the cooler areas of the tropics.
• The adult is an aphid-like insect about 2mm long with transparent wings almost twice the length of the body.

Damage

• The leaves are conspicuously pitted, the pits opening the lower leaf surface.
• In severe attacks, young blades are cupped or otherwise distorted and yellow in color.
• Leaves with many picks tend to curl upwards.
• Citrus psyllid causes serious problems by transmitting a bacterium causing greening disease.
• Leaves get interveinal yellowing, narrowing of leaves and leaves stand upright with plant dieback.
• The plants become less productive and fruits are underdeveloped.
• The disease is mainly spread by scion/bud materials.

Control

• Pruning off infected braches can slow disease development.
• General insecticides like sumithion, salut, decis, dimethoate and dursban can be used to control insects.

Aphids

These are shiny black brown insects and may be winged or wingless.

The main injuries caused by aphids on citrus are

• Severe curling and deformation of young leaves
• Stunted growth of leaves and twigs
• Some branches and twigs show dieback symptoms
• There is impairment of leaf functionality from the presence of sooty mould fungus which grows in copious quantities of honey dew excreted by the aphids

Control

• Spray should only be applied in periods of flush growth and before populations build up (before much curling of leaves).
• Spray using dimethoate, fenitrothion or pyrethroids.
• Some contact pesticides like dursban may be used during heavy infestation.

Orange dog

• Adult is a dark brown butterfly with numerous pale yellow markings.
• The caterpillar has 5 stages and all are harmful.
• The first 3 are dark brown with white markings and resemble bird droppings.
• The fourth and fifth stages are pale green caterpillars with black, brown and grey markings.
• If the caterpillars are disturbed, they secrete a pink Y shape organ from right behind the head.

Control

• Remove and kill the caterpillars found on young trees.
• Where infestation is high, spray using dimethoate.

Other pests include

• Citrus woody white fly
• Scales
• Thrips
• Mites
• Mealybugs
• Nematodes

Diseases

Oranges are attacked by many fungal diseases especially when grown under hot, humid conditions.

These include;

• Bacterial citrus canker
• Leaf and fruit spot
• Melatose
• Scab
• Stem and end rots
• Phytophthora
• Penicillium

Control

• Sprays with fungicides are recommended to control fungal diseases using such chemicals like copper oxychloride, kocide, benlate or rodomil.
• These chemicals may have to be used in combination depending on the diseases present.
• Viruses also attack orange plants where the most deadly is Ctv-citrus tristeza virus transmitted by aphids.
• The aphids are controlled using insecticides mentioned above.
• Whereas quick decline is caused by aphids, spreading decline is caused by nematodes.
• The nematodes can be controlled using furadan, nemacur or temik.
• For bacterial citrus fruit canker, spray with a copper based bactericide.
• Also defoliating of crops affected by bacteria canker and destroying the leaves reduces diseases incidences.