CITRUS AGRONOMY

BYDennis Owusu Boateng (Technical officer)BUNSO COCOA COLLEGECSSVD CONTROL UNIT (COCOBOD)

Introduction

• Botanical name for sweet orange iscitrus senensis• Citrus, common name for several related evergreen

trees and shrubs of the Rue family, and generally forthe fruits they produce, including the citron, grapefruit,lemon, lime, orange, shaddock, tangerine, andlemon, lime, orange, shaddock, tangerine, andbergamot (Apear shaped orange).

• The plants are characterized by wing like appendageson the leaf stalks, white or purplish flowers, and fruitwith a spongy and a juicy pulp divided in sections.

• The leaves, flowers, and rind of the fruit abound involatile oil and emit a sharp fragrance. Many citrusplants have thorny branches.

Distribution

♦ Citrus are subtropical, with growingtemperatures ideally at 24-27 ºCand intolerantof frost.

♦ Nativeto SoutheastAsia♦ Nativeto SoutheastAsia

♦ Site selection, always an importantconsideration, is particularly critical in regionssubject to cold winter temperatures.

♦ Major citrus production worldwide

Botany

♦That is the biological descriptionof aplant.

♦The citrus tree consists of

�Shoot,

�Leaves,

�Flowers,

�Fruits and

�Roots.

Flowers

♦ Reproductive organ of most seed-bearing plants.Flowers carry out the multiple roles of sexualreproduction, seed development, and fruitproduction.

♦ The flowers are solitary or in small corymbs,each flower 2–4 cmdiameter, with five (rarelyfour) white petals and numerous stamens; theyare often very strongly scented.

Leafs♦ A leaf is an extension of a plant's branch.

♦ A plant leaf helps in transpiration andguttation, both of which remove excess waterfrom the plant, and respiration, the process bywhicha plantobtainsoxygenandenergy.whicha plantobtainsoxygenandenergy.

♦ Leaves also may store food and water andprovide structural support.

♦ These plants are large shrubs, reaching 5–15 mtall, with spiny shoots and alternately arrangedevergreen leaves with an entire margin.

♦ Leaf Arrangement

Fruits

♦ The fruit is ahesperidium, a specialised berry,globose to elongated, 4–30 cmlong and 4–20cm diameter, with a leathery rind surroundingsegments filled with pulp vesicles.

♦ Citrus fruits are notable for their fragrance,partly due to flavonoids and limonoidscontained in the rind, and most are juice-laden.

♦ The juice contains a high quantity of citric acidgiving themtheir characteristic sharp flavour.

Varieties

• Citrus consists of many species, some of whichare not even edible. Some varieties of the edibleones have however been recommended to thepublic.

• These include:• These include:– Sweet Orange– Grapefruit– Tangerine– Tangelo– Lemon– Lime

Propagation

♦ Citrus is almost entirely propagated bybudding. Planting unbudded seedlings may notbe true-to-type, and often takes a long time tofruit.fruit.

♦ They are also susceptible to disease attack.

♦ Obtain buding by selecting a required bud anduniting this with a suitable rootstock.

♦ Most trees are propagated in the nursery by T-budding.

Picture showing T budding

♦ ROOTSTOCKS♦ Traits most important in rootstock selection

include:– compatibility with scion

– adaptation to soil and climatic conditions

– easeanduniformity in propagation– easeanduniformity in propagation

– influence on precocity, consistent cropping andyield, and fruit quality

– influence on winter hardiness

– suckering tendency

– sensitivity to disease, pests, and replant problems.

Selecting a site for Nursery♦ The site should be level.♦ It should be safe fromerosion, floods or heavy winds—that

is, you will need windbreaks.♦ It must be fenced to protect it against damage fromanimals.♦ It needs a permanent water supply.♦ It mustbeneara roadfor transportof inputsandplantsand♦ It mustbeneara roadfor transportof inputsandplantsand

ready access by clients.♦ The soil used must be free of soil borne diseases and pests,

such as nematodes.♦ Local construction materials, such as wood, bricks, poles

and banana stems, should be available.♦ Labour to manage the nursery must be available.♦ Well-rotted farmyard manure, sand or decomposed sawdust,

compost or fertile topsoil for soil mixture must be available.

Site selection and Preparation

• Sandy loamis best for the cultivation of Citrus.• The most important factor in the choice of site

is free fromhigh drainage of water.• Soils with an underlyinghardpanof about1m• Soils with an underlyinghardpanof about1m

or less to the top mock soils, or slain sites arenot suitable. Apart fromthese, citrus can begrown on a wide range of soil types.

• Citrus is not shade loving, therefore clear thesite of all tree stumps and plough beforesetting in the plants.

♦ Citrus can develop a large number of nutrientdeficiencies, including N, P, K, Mg, Ca, Mn,Zn, Cu, Fe, B and Mo.

♦ The level of N fertility has more influence onthe growth, yield, and quality of citrus thananyothersingleplantnutrient.anyothersingleplantnutrient.

♦ Adequate supplies of N are necessary tooptimize growth and development of newlyplanted citrus trees.

♦ Compost, animal manure and green manurecan be worked into the soil to a depth of 1 m,to serve as pre plant fertilizer.

Orchard Establishment

• Plant the orchard when the rainy season hasfully set in.

• Clear the land of any bush.

• Complete planting holes, well in advance,• Complete planting holes, well in advance,before purchasing the budding.

• Always ensure that the trees are planted nodeeper than they had grown in the nursery.

• Citrus has a planting distance of 3m x 3m

How to Plant

♦ Prepare the planting hole– Dig a hole only as large as necessary to

accommodate the root system.

– Treesshould be plantedwith their top major– Treesshould be plantedwith their top majorroots even with the soil line.

– Prune any damaged roots back beyond thedamaged area.

– If container-grown trees have a tap root curledin the bottomof a container, cut this root off atthe point where it begins to curl.

– Separate and trimthe roots of container trees thatmay be root-bound.

– Save the soil fromthe hole to use as backfill.

• Position the tree– Place the tree in the hole at the same depth it was

growing previously.

♦ Filling the hole– Remove any debris fromthe dug-up soil. Back-fill

with the same soil that was removed fromthe hole.Never back-fill with an amended soil mix of alighter texture. Such a practice will create drainageproblems and cause tree roots to suffocate duringperiods of excessive moisture.

♦ Water– After the tree is planted, water well. Check the

original soil line one last time.

– If the tree does settle, nowis the time to move itback to the correct position with the soil level .

♦ Stake if needed– Unlessthetreebendsover,it will not needsupport– Unlessthetreebendsover,it will not needsupport

from staking.

– If stakes are needed, place themon opposite sidesof the tree, perpendicular to the direction of theprevailing wind.

Before Planting After planting

Maintenance Operations1. Training and Pruning (Nursery)

– The tree must produce a canopy of sufficient sizebefore economic fruit production begins.

♦ What to do during training and pruning.– Removeshoots(i.e. suckers)originating from the– Removeshoots(i.e. suckers)originating from the

rootstock and lowon the scion (i.e. water sprouts)

– Remove branches that cross fromone side of thetree to the other.

♦ This will produce an abundance of vegetativegrowth that will, in turn, assist in producingnewvegetative growth.

2. Irrigation(Nursery)– Young trees seldom need watering in the fall. For

young trees, it is best to water twice per week, from March through June is to maintain optimum moisture in the upper soil layer where most of the roots are, especially during the crucial period of leaf expansion, bloom, fruit set and fruit leaf expansion, bloom, fruit set and fruit enlargement –(January/February to June, usually).

– Soil type will affect how well the soil holds the water.

♦ Good irrigation help– Proper growth and fruiting it is essential that trees

receive water in ‘on time’.

– To ensure adequate moisture the soil should be thoroughly wet before wilting occurs.

– To avoid overwatering, excess water must drain – To avoid overwatering, excess water must drain away.

– Alternate wetting and drying allows oxygen necessary for root growth to enter the soil.

3. Fertilizing (Nursing)– Mineral nutrients are classified as macronutrients

and micronutrients.

– The term "macronutrients" refers to thoseelements that plants require in large amounts (N,P, K, Ca, Mg, S).

– The term "micronutrients"(or “trace elements”)– The term "micronutrients"(or “trace elements”)applies to plant nutrients that are essential toplants but are needed only in small amounts (Fe,Zn, Mn, B, Cu, Mo, Ni, Cl).

– Visual deficiency symptoms of N, P, K, Ca, Mg,Fe, Zn, Mn, B, Cu, and Mo can usually berecognized by distinctive symptoms with lack ofnutrients.

♦ Types of fertilizer to use:

Generally, only two types of fertilizers are required: – A balanced fertilizer (8-8-8, 13-13-13), and

– A nitrogen fertilizer such as ammonium nitrate (33-0-0), or ammonium sulfate (21-0-0). Urea (46-0-0) is a good source of nitrogen. The nitrogen 0-0) is a good source of nitrogen. The nitrogen fertilizer stimulates vegetative growth later in the year. The numbers 8-8-8 or 13-13-13 represent the percentage of nitrogen-phosphorus-potassium the fertilizer has.

4. Weeds Removal (Nursing)– Hand pick weed and unwanted plants from the

nursery.

– These weeds compete with the citrus for nutrients which may end up killing the seedlings.

5. Pest Control (Nursing)5. Young Plants at nursery are affected by a lot of

stem borers, Leaf Chewers and leaf miners.

6. Recommended insecticide such as Green Light Spinosad can be sprayed

Orchard Management

The activities for citrus management include:

♦ Pruning

♦ Irrigation

♦♦ Weed Control

♦ Fertilizer Application

♦ Pests, Parasites and Diseases , and their control

♦ Pruning (Matured Stage)– For a matured tree, we do want is called

maintenance pruning. This is a situation were wedo selective pruning; If heavy pruning of largewood is required, pruning half of the trees in thefirst year, and the second half next year will reducetheimpactof croploss.theimpactof croploss.

♦ Annual pruning of diseased and pest attackedbranches is also done in the matured stage.

♦ To avoid damage to the fruit, mature fruit treesshould not be pruned immediately beforeharvest, or when mature fruit are on the tree inearly spring.

♦ Irrigation (Matured Stage)– Citrus trees will wilt and yield will be depressed

unless moisture is provided during the long dry season of November to February.

– Therefore, make sure that the trees are watered during this period.

– Ten liters of water (stream water, well water, tap – Ten liters of water (stream water, well water, tap water, etc.) delivered at the base of the trees twice a week is sufficient for good development and yield.

♦ Weeding (Matured Stage)– Absolute weed control under a hot, humid climate

may be very expensive, nevertheless there is needfor some level of weed control.

– Slash the orchard at least 3 times in the year witha hoe, the last being at the on-set of the dryseason.season.

– In addition, ring weed individual trees constantly.Ring-apply Diuron or Paracol to check weedgrowth.

♦ Fertilizer Application (Matured Stage)– 2–4 years of age:

• 500 grams of compound fertilizer N.P.K (15:15:15) per trees, twice in the year.

– 5–10 years of age:• 2 kg (15:15:15) + 600 grams per tree, twice in the year.

– 10 years and above: – 10 years and above: • 3 kg (15:15:15) + 800 grams per tree, twice in the year.

♦ These applications should be done in June and September to obtain maximum benefit.

Pests of citrus

♦ Citrus Rust Mites♦ Main Species

– Citrus bud mites

– Citrusredmites– Citrusredmites

♦ Symptoms of Damage– causing external blemishing and, in extreme

infestations, smaller fruits, pre-mature fallingand even shedding of leaves. disfigure thesurface of the fruit and the foliage mainly in thewinter and during droughts

♦ Biological Control– Mass rearing and release of parasitic fungi

(Hirsutella thompsonii and Triplosporiumfloridana) help to eradicate rust mites and theTexas citrus mite.

♦ Chemical Control– To controlCitrusBud Mites spraythetreewith– To controlCitrusBud Mites spraythetreewith

Bug Buster or Trounce.

Picture of Citrus Rust Mites

Citrus Scale Insects

♦ Main Species– Snowscale, Purple scale, Red scale and glover

scale.

♦ Symptomsof damage♦ Symptomsof damage– Affect woody portions of the tree, suck sap

from the branches, twigs, leaves and fruit,induce shedding of fruit and foliage, producesgreen spots on the fruit, infests young trees.

♦ Biological control– Maintaining populations of the Vedalia lady

beetle in nurseries and groves is a fairlyeffective means of controlling this scale,Parasitic wasps (Aphytis spp.) are able tocontrol Citrus snow scale, purple scale andFlorida red scale.

♦ ChemicalControl♦ ChemicalControl– To effectively control scale insects and limit

damage, Horticultural Oil should be sprayed onthe tree. The Horticultural oil serves tosuffocate the scale and eggs. In the spring if thecrawling nymphs are present, spray the treeswith Bug Buster to prevent the newnymphsfrom further infecting the tree.

Picture of Citrus Scale insect

Citrus Aphids (Plant lice)♦ Main Species

– Brown Citrus aphid,Toxoptera citricidus

– Citrus Whitefly

– Orangedogcaterpillar– Orangedogcaterpillar

♦ Symptoms of Damage– Aphids (plant lice) cause leaves to curl,

crinkled with puckered marks, yellowing andthe twisting of the leaves, which gives theappearance of deformed leaves. As the severityof the aphid infestation increases, leaf drop andtwig and branch die back can be seen.

♦ Chemical control– Use a specific aphicide or horticultural spray

oil. Always check the label before spraying, asnot all oils are registered for use in citrus. Oilscan also cause phytotoxic damage if not usedcorrectly.

♦ Biological control♦ Biological control– Predators, parasites, and fungal diseases attack

aphids and occur naturally in the orchard. Thehoneydewproduced by the aphids provides agood food source for many natural enemies.

Picture of Citrus Aphid

Fruit Flies

♦ Main Species– Queensland fruit fly

– Mediterranean fruit fly

– Papayafruit fly– Papayafruit fly

♦ Symptoms of damage– Infested fruit usually falls fromthe tree as a

result of the activity of the larvae in it. Thestyle of damage by fruit fly larvae tunnelling infruit varies with the type and maturity of thefruit, the number of the larvae in it, and the

– weather . Frequently citrus fruits, althoughstung, do not develop larvae, but the stung fruitsometimes fall.

♦ Control– Traps

• Traps are used to monitor male fruit fly populationsin orchards. The lures in the trapsattractonly thein orchards. The lures in the trapsattractonly themale fruit fly, which are then killed.

• The traps, commonly called Dak-pots, contain amixture of the male attractant or parapheremone andan insecticide.

• The traps are normally hung in trees. The traps areeffective and convenient but do not control it.

– Baits• Bait mixture is prepared using an attractant (protein

source) and an insecticide. Flies are attracted to theprotein which they require for egg maturation.

• As they feed they are killed by the insecticide. Baitspray components include the insecticides maldisonor chlorpyrifos and yeast autolysate or hydrolysateastheattractant.astheattractant.

– Chemical spray• Registrations also exist for the chemicals dimethoate

and fenthion for cover sprays for Qld fruit flycontrol in citrus.

Picture of Citrus Fruit Fly

Diseases of Citrus

♦ Citrus Canker♦ Causative organism-Bacterium♦ Symptoms

– formation of scabs(similar to halo lesions)in– formation of scabs(similar to halo lesions)inthe leaves, branches and fruits causing yellowhalo-like lesions or scabs on the fruit, leavesand twigs of citrus trees. Severe infections cancause leaf loss, blemished fruit, fruit drop anddie back.

♦ Control– This contagious disease is treated by applying

antibiotic formulation.

– Management options include replacingsusceptible citrus cultivars with resistantcultivars, applying preventive sprays of copper-based bactericides, and destroying infectedbased bactericides, and destroying infectedtrees and all surrounding trees within anappropriate radius.

Picture of Citrus Canker

♦ Citrus Sooty Mold♦ Causative organism-fungus♦ Symptoms

– Characterized by black coloration of theaffected citrus tree leaves. The black color isnothing but the spores of sooty mold.

– The mold forms on the leavesas a result of– The mold forms on the leavesas a result ofhoneydew secretions from insects such aswhiteflies, aphids and mealybugs.

♦ Control– Using formulations of neemoil, which is an

organic broad spectruminsecticide, fungicideand miticide such as orthene, malathion, ordiazinon

Picture of Citrus Sooty Mold

♦ Citrus Greasy Spot♦ Causative organism-fungus♦ Symptoms

– After infection takes place, the fungal sporesgerminate within the leaf tissues, causing thelower leaf portion to develop slightly raisedblisters.blisters.

– Telltale signs include yellowish-brownishblister spots on leaves, often on the undersideof the leaf. As the disease develops, the spotsdevelop into oily looking blisters.

♦ Control– Spraying copper fungicide two times in

summer help in controlling this fungal disease. Spraying petroleum oil at the rate of 5-10 gallons per acre is generally applied.

Picture of Citrus Greasy Spot

♦ Citrus Melanose♦ Causative Organism-fungus♦ Symptoms

– Darkly colored, raised, corky pustules appearafter leaf infection. The pustules may besurrounded by yellowed leaf tissue or yellowhalos. The yellow color may later turn green.halos. The yellow color may later turn green.Severely infected shoot apices may becomedistorted or die back.

– Fully expanded, mature leaves resist infection.On fruits infection appears as darkly coloredand usually raised pustules of various sizes

♦ Control– Cultural control by periodically pruning away

dead branches. This will reduce pathogensurvival, increase air circulation to dry out thecanopy, and allowfor more effective fungicidepenetration and coverage of the foliage.

– Spraysof copper fungicides to young fruits– Spraysof copper fungicides to young fruitsand leaves may be necessary for diseasemanagement. Where the disease tends to besevere, frequent fungicide applications may berequired

Picture of Citrus Melanose

♦ Citrus Root Rot Disease♦ Causative organism-Fungus♦ Symptoms

– Notable signs include developing brownpatches in bark, oozing of plant sap, leafturning yellow, premature leaf fall andbrowningof citrusfruits.browningof citrusfruits.

– Over time, as the disease advances the barkdries, cracks and dies. The infected area is thenleft as a dark sunken canker. The disease canalso cause browning and decaying on the fruitand yellowing and die-back on the foliage.

♦ Control– Cultural control such as trimming down all the

affected twigs and spray appropriate fungicidein correct dose. To control the brown rot it isimportant to remove all leaves and damagedfruit when it falls to the ground; prune of alllower branchesoff the tree so that the treelower branchesoff the tree so that the treebranches are more than 2 feet fromthe ground;

– Chemical control can be done by spraying thetree with a fungicide such as Agri-Fos andCaptan

Picture of Citrus Root Rot

Parasite

♦ Mistletoes– Mistletoes are plant parasites that live on other

plants to obtain food and water.

♦ Carrierorganism- Birds,squirrelsand♦ Carrierorganism- Birds,squirrelsandporcupines

♦ Symptoms– The symptoms are difficult to note at the early

stage because the leaves mimic that of citrus. itcan really be seen when the parasitic plant bearsyellow or red flowers at the adult stage.

♦ Control– Cultural control is so far the only method that is

effective; chemicals are not effective, as it isimpossible to apply themsafely and efficiently.This is done with a standard pruner

– The recommended time is when the Mistletoe isin flower asthis makesit easierto spottheminin flower asthis makesit easierto spottheminthe cocoa canopy.

Picture of Mistletoes

Harvest

♦ Citrus must be clipped, not pulled fromthetree, to prevent plugging the peel. It is bestto harvest citrus on a clear, sunny day withlow humidity. The fruit shouldbeharvestedlow humidity. The fruit shouldbeharvestedas soon as the dewhas evaporated. On acloudy day, the fruit should be harvested inthe afternoon. Fruit should not be harvestedat all on a rainy day.

Storage♦ Only fruit which have not been damaged in

harvest are used for storage. Citrus may bestored for periods of up to 1-2 months atlow temperatures (0-4.4 °C).

♦ Plasticcratesor boxesare usedfor storing♦ Plasticcratesor boxesare usedfor storingfruit. Boxes should be stacked inside thestorage roomin a way that maintains goodventilation. Fruit will store longer if keptcold. Sunlight should not be able topenetrate inside the storage room. Anyrotting fruit should be removed.

Uses♦ Food Value

– Their juice is used as an ingredient in a variety ofdishes; it can commonly used in salad dressings andsqueezed over cooked meat or vegetables.

– A variety of flavours can be derived from different– A variety of flavours can be derived from differentparts and

– Marmalade, a condiment derived fromcooked orangeand lemon to produce a jam-

– Lemon or lime is commonly used as a garnish forwater, soft drinks, or cocktails.

– The colourful outer skin of some citrus fruits, known aszest, is used as a flavouring in cooking;

♦ Medical Value– Citrus juice also has medical uses; lemon juice is used

to relieve the pain of bee stings.

– Oranges were historically used for their high content ofvitamin C, which prevents scurvy.

– After consumption, the peel is sometimes used as afacial cleanser.

– A peel of lemons or orange is commonly used as ameans to moisten medical cannabis when stored with it.

– Before the development of fermentation-basedprocesses, lemons were the primary commercial sourceof citric acid.

– Orange juice may help prevent calciumoxalate stoneformation

ME’DAASE