A Rutaceae plant: - “Citrus”

Dronak Kumar Sahu (Ph.D. Scholar, Agricultural Economics) & Yogesh jain (B.Sc. Horticulture), Indira Gandhi Agricultural University, Raipur

Citrus is a genus of flowering trees and shrubs in the rue family, Rutaceae. Plants in the genus produce citrus fruits, including important crops such as oranges, lemons, grapefruits, pomelos, and limes.

1. Introduction

Citrus is native to a large area, which extends from Himalayan foot hills of northeast India to northcentral China, the Philippines in east and Burma, Thailand, Indonesia and New Caledonia in Southeast. In India, in terms of area under cultivation, citrus is the third largest fruit crop after Banana and Mango. The average yield of citrus fruits in India is alarmingly low (8.8 t/ha) compared to other developed countries like Indonesia, Turkey, Brazil and USA (22-35 t/ha). Among mandarins, Nagpur mandarin (Central India), Kinnow mandarin (North–West India), Coorg mandarin (South India) and Khasi mandarin (North-East India) are the commercial cultivars of India. Whereas, Mosambi (Maharashtra), Sathgudi (Andhra Pradesh) and Malta and Jaffa (Punjab) are the sweet orange cultivars traditionally grown.

2. Scope for Citrus Cultivation and its National Importance

Citrus cultivation in India is plagued with various problems due to limiting growing conditions, limiting water resources and high incidence of pests and diseases warranting great care from planting till the plants come to bearing in order to sustain a productive life of a minimum of 15-20 years. There is growing interest/awareness among the citrus growers for adoption of latest technologies for commercial cultivation of citrus. The National Research Centre (NRC) for Citrus (ICAR), Nagpur has come out with the package of practices for citrus cultivation in different regions of the country. In the present bankable project on citrus, recommendations of the NRC for Citrus and the views of the citrus growers and their experience has been taken into consideration.

3. Technical Requirements of Citrus Cultivation

1. Climate

Citrus fruits in India are cultivated under varied agro-ecological conditions right from arid and semiarid areas of southwest region to humid tropical climate of northeast India. Citrus trees are evergreen, grown in truly subtropical climates of the world although in tropical regions of the world they tend to produce cyclic growth flushes and hence regulating cropping in tropical areas for forcing them into concentrated bloom needs judicious management of water deficit stress according to soil type and growing season. Citrus fruits grow best between a temperature range of 130C to 370C. Temperatures below – 4 0C are harmful for the young plants. Soil temperature around 250C seems to be optimum for root growth. High humidity favours spread of many diseases. Frost is highly injurious. Hot wind during summer results in desiccation and drop of flowers and developing fruits. Barring these limitations citrus is grown in all subtropical and tropical areas of the world. The subtropical climate is best suited for citrus growth and development. Khasi and Darjeeling mandarins are grown in high altitudes upto 2000 m as it is adapted to a cooler climate.

2. Soil

Citrus plants are grown in a wide range of soils ranging from sandy loam or alluvial soils of north India to clay loam or deep clay loam or lateritic/acidic soils in the Deccan plateau and north-eastern hills. Citrus orchards flourish well in light soils with good drainage properties. Deep soils with pH range of 5.5 to 7.5 are considered ideal. However, they can also be grown in a pH range of 4.0 to 9.0. High calcium carbonate concentration in feeder root zone may adversely affect the growth. 3.3 Planting Material Availability of quality planting material is of utmost importance in citrus cultivation. Citrus plants are very sensitive to various biotic and abiotic stresses. Therefore selection of an ideal rootstock is a continuing challenge for the citrus industry of India. Currently used rootstocks viz. rough lemon and Rangpur lime have gone through a lot of variation over the last five decades. Therefore ideal selections developed from the conventional rootstocks by National Research Centre for Citrus (NRCC), Nagpur and at other places under State Agriculture Universities may be obtained for propagating quality planting material. For budwood selection, disease free mother plants developed from the elite progeny of known pedigree through shoot tip grafting method available at NRCC, Nagpur may only be used.

Primary nursery beds are prepared on light fertile soils or in the HDPE trays under shade net structures. Selection of nucellar seedlings is done by eliminating weak seedlings, off types and non uniform seedlings in 2-3 stages in the nursery beds. Secondary nursery seedlings may be raised in polythene bags also as they become ready for plantation in the main field after attaining the height of about 30-40 cm after one year.

4. Land preparation

Land needs to be thoroughly ploughed and levelled. In hilly areas, planting is done on terraces against the slopes and on such lands, high density planting is possible as more aerial space is available than in flat lands. Since citrus trees are highly sensitive to water logging and water stagnation during rainy season providing drainage channels of 3-4 feet depth along the slopes around the orchard is essential.

5. Plant density

a. Mandarin (Citrus reticulata Blanco)

Normal spacing – 6 m x 6 m ; Plant population – 277 / ha

b. Sweet orange (Citrus sinensis Osbeck)

Normal spacing - 5 m x 5 m, 5.5 x 5.5 m; Plant population – 400/330 per ha

c. Limes/lemons (Citrus aurantifolia Swingle & Citrus limon)

Normal spacing – 6 x 6 m / 5 x 5 m, Plant population – 277/400 per ha In light soils, spacing will be 4.5 x 4.5 m or 5 x 5 m.

6. Planting

The best season of planting is June to August. Pits of the size of 1m x 1m x 1m may be dug for planting seedlings. 15-20 kg of FYM and 500 g of super phosphate is applied per pit while planting. With good irrigation system, planting can be done in other months also.

7. Irrigation

Citrus requires critical stage watering in the initial year. It further reduces fruit drop and increases the fruit size. Diseases like root rot and collar rot occur in flooded conditions. Light irrigation with high frequency is beneficial. Irrigation water containing more than 1000 ppm salts is injurious. Quantity of water and frequency of irrigation depends on the soil texture and growth stage. Micro irrigation systems not only saves water and nutrients but also ensure good retention of fruits during crucial stages of crop growth in March – April even in situations where water is not a limitation.

8. Manures & fertilizers

Manuring is done in three equal doses three times in a year in February, June and September. The recommended manurial and fertilizers doses are given in Table 4 & 5 respectively.

9. Interculture

Ploughing, spading of basins, weed control, etc., are important inter-culture operations for soil aeration and health. Chemical control of weeds with pre-emergence weedicides like diuron (3 Kg/ha), simazine (4 Kg/ha), glyphosate 4 l/ha, paraquat (2 l/ha), etc. may also be adopted.

10. Intercrops

Leguminous crops like soybean, gram, groundnut, cow peas, french bean, peas etc., may be grown in citrus orchards. Intercropping is advisable during the initial three-four years after planting.

11. Training and Pruning

In order to allow the growth of a strong trunk, initially shoots upto 40-50 cm from the ground level should be removed. The centre of the plant should remain open. Branches should be well distributed to all sides. Cross twigs and water suckers are to be removed early. The bearing trees require little or no pruning. All diseased, injured and drooping branches and dead wood are to be removed periodically.

12. Pests and Diseases Management.

12.1 Pests

Important insect-pests of citrus are citrus black fly and whitefly, citrus psylla, Citrus thrips, leaf miner, scale insects, bark eating caterpillar/trunk borer, fruit fly, fruit sucking moth, mites, etc. Other pests attacking citrus particularly mandarin orange, specially in humid climate are mealy bug, nematode, etc. Control measures of major pests are indicated below:

Leaf miner: Foliar sprays either with quinalphos 1.25 ml or fenvalerate 0.5 ml or monocrotophos 1.0 ml/litre of water at weekly intervals on new flush as soon as infestation is noticed.
Citrus black fly and white fly: One spray against adults and two at 50% egg hatching stage (I half of April & Dec. and II fortnight of July) at 15 days interval either with acephate 1.25 g or quinalphos 1.5 ml or imidacloprid 0.5 ml/ litre of water.
Citrus psylla: Foliar spray either with quinalphos 1.0 ml or acephate 1.0 g or monocrotophos 0.5 ml/litre of water at bud burst stage or as and when infestation is noticed during Feb, - Mar., Jun., - Jul. & Oct, - Nov.
Citrus thrips: Foliar spray either with dimethoate 1.5 ml or monocrotophos 1 ml/litre of water at bud burst stage and berry size fruits. Scale insects: Spraying of parathion (0.03%) emulsion, dimethoate 150 ml and 250 ml kerosene oil in 100 litre of water or malathion @ 0.1 % or carbaryl @ 0.05% plus oil 1 %. Trunk borer: Swabbing of tunnel either with dichlorvos (0.1%) or carbaryl (1%) or monocrotophos (0.02%) kills the grub effectively.
Bark eating caterpillar: Plugging of larval tunnels with cotton wad soaked either in dichlorvos (0.1%) or carbaryl (1%) or monocrotophos (0.01%) effectively checks the pest.

12.2 Diseases

The important diseases of citrus are Phytophthora gummosis, citrus tristeza virus, citrus greening (HLB-Huang Long Bing), citrus canker, powdery mildew, anthracnose, etc. Control measures of these diseases are stated briefly below:

Phytophthora Gummosis: Scraping of the affected area and application of Bordeaux paste or copper oxifluoride paste or ridomil + carbendazim. Citrus greening (HLB--Huang Long Bing): Removal of infected branches/unproductive trees and their replacement by disease-free plants. Application of ledermycin 600 ppm with ZnSO4 and FeSO4.Meticulous control of citrus psylla vector.

Citrus tristeza virus: Control of aphids and use of cross protected grafts and shoot tip grafted plants or disease free grafts are recommended.

Citrus canker: Cutting of infected twigs followed by spraying of 1 % Bordeaux mixture or copper fungicide. Foliar spray application of 100 ppm streptomycin sulphate is also effective. Powdery mildew: Pruning of dead twigs followed by foliar spray of wettable sulphur @ 2 g/litre, copper oxychloride @ 3 g/litre of water in April and October.

Anthracnose: Pruning of dead twigs followed by two foliar sprays of carbendazim @ 1 g/litre or copper oxychloride - 3 g/litre at fortnightly interval.

13. Harvesting

There are two main crops in mandarins and sweet oranges. One is called as Ambiabahar (mango flowering) the flowering of which occurs in the month of January (at the time of flowering of mango hence the name Ambia) the fruits of which are available in the months of October-December The other crop is Mrigbahar(Monsoon bloom) the flowering of which occurs in the month of June-July and the fruits are harvested during February-April. Mandarins and sweet oranges normally take 240- 280 days to arrive at maturity. Mature fruits at colour break stage are picked up in 2 - 3 intervals of 10-15 days. Limes and lemons take 150-160 days for maturity. There may be 2 or 3 crops in a year in limes and lemons.

14. Yield

Mandarin: Commences from the 5th year with about 50 fruits per tree and stabilises in the 8th year. Average production is about 700-800 fruits per tree after stabilisation.

Sweet Orange: Commences from 5th year with 40-50 fruits per tree& stabilises around the 8th year. Average production is about 500-600 fruits per tree after stabilisation.

Lime/Lemon: Commences from the 3rd year with 50-60 fruits per tree & stabilises in the 8th year. Average production is about 1000-1500 fruits per tree after stabilisation.