The importance of navel oranges

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Citrus origin and its production

Citrus (Citrus sinensis L.) is a very ancient crop known to have been in existence over 4000 years ago (Mukhopadhyay, 2004). Whiteside et al. (1998) revealed that all citrus fruits originated and are native to south eastern Asia. According to Mitra (1997), oranges are grown in tropical, subtropical and temperate regions that have a suitable climate and such regions are within the latitude of 41°N and 34°S. Rieger (2006), indicated that in 2004 sweet orange production was at 63,039,736 MT or 139 billion pounds. Brazil is now the largest producer of citrus world-wide and its industry is orientated towards production of oranges for processing.
The United States of America, China and Spain, are other largest citrus producing countries followed by Mexico, Italy, Japan, Egypt, Argentina, Turkey, Israel and Morocco (PPECB, 2009). Although South Africa is one of the smaller producers by world standards, it sets the example on the production, development and export of citrus fruit and products amongst the southern hemisphere countries which include the continents of Australia and South America ( 2010). Citrus production in South Africa has been indepthly discussed in the preceding chapter.

Taxonomy of citrus (Citrus spp.)

The genus Citrus belongs to the Rutaceae or Rue family, subfamily Aurantoideae (Rieger, 2006). This author also mentioned that the Rue family has 150 genera and 1600 species worldwide. Ray and Walheim (1980) and Rice et al. (1992) described citrus as a deciduous to evergreen tree or shrub with sharp spines; leaves are unifoliate, alternate, coriaceous or curtaceous and punctuate with aromatic pellucid glands; flowers are solitary, in cymes or racemes, small or large, bisexual or staminate and sweet scented. These authors further asserted that flowers are cross pollinated and fruits are segmented hesperidia containing seeds near the ventral side and stalked, fusiform; pulp vesicles contain sweet or sour juice. The rind consists of an outer coloured portion called flavedo and an inner white spongy portion called albedo. The flavedo contains many oil glands and it turns yellow or orange or red at full maturity (Ortuño et al. 2005). There may be no seed or there may be many seeds attached to the outer wall of each segment. The seeds contain one or more white or green embryos that are produced asexually by mitotic division of the nucellus.

Citrus sinensis

Citrus sinensis is a binomial name for sweet oranges (Oliveira et al. 2005). Sweet oranges are categorised into four groups namely; common oranges, blood oranges, navel oranges and acid less oranges (Jackson, 1999). Valencia, torocco, navel and succari are examples of common, blood, navel and acid less oranges respectively (Nunes, 2008). Yadav (2007) ranked sweet oranges as second important crop in citrus. Out of the four groups of sweet oranges, navel is the most commonly planted type of orange in the Eastern Cape midlands (Statistics South Africa, 2002).

 Navel oranges

Navel oranges develop from a secondary ovary embedded within the usual ovary and as the second ovary enlarges, it also causes the navel orange to enlarge (Ray and Walheim, 1980). Navels are generally seedless and make excellent quality fresh fruits with a crisp, rich flavour and ease of peeling and separation. They are among the finest table fruits, and certainly the standard of excellence among sweet oranges.

The importance of navel oranges

The sweet orange (Citrus sinensis) is one of the world‟s most important fruit crop which is consumed mostly as fresh produce or juice (Liu and Deng, 2007). From ancient time, its nutritional significance was well known particularly as the principal source of vitamin C and folic acid (Oben et al. 2009). Fresh oranges are rich in vitamin C which plays a vital role in prevention of scurvy and other human related illnesses. Mitra (1997) also confirmed the nutritive significance of oranges by stating that orange flavonoids namely; naringin, rhoifolin, lomcerin, hesperidin, neohesperidin, citronin and tangeretin are located in the rind and juice segments of an orange.
Mukhopadhyay (2004) indicated that the flavonoids have the ability to prevent invasion of normal tissues by cancer cells and added that orange hesperidin, naringin, tangeretin and nobiletin have anti-inflamatory and anti allergic properties and these flavonoids also improve circulatory system. This author declared that oranges‟ therapeutic and nutritive values along with its taste and flavour have placed it in the regular dietary list of the people living in advanced countries.

Citrus pests

Rice et al. (1990), stipulated that, a number of insects attack citrus but the severity of damage varies with location and predator population. Peña, et al. (2002) listed about 875 insects and mites, albeit less than 10 % are of major concern. These authors listed the most serious pests for citrus as scales (soft brown, green and wax scales), mealybugs, fruit flies (Mediterranean and Natal fruit flies), thrips, mites (citrus red mites), aphids (black and brown aphids), citrus leafminer, false codling moth and citrus psyllid.
Helicoverpa armigera is among lepidopterous pests which are classified as fruit borers (Moore et al. (2004). This pest is among the many pests that are problematic in the Eastern Cape midlands and if not controlled can cause huge decline in orange yields.

The Helicoverpa armigera

Helicoverpa armigera is present in most of mainland Europe, Asia, Africa and Australasia (Venette et al. 2003). This notorious and well known pest is extremely polyphagous and is a major pest in Southern Hemisphere (Prinsloo, 1984). Moore et al. (2004) declared H. armigera as the pest which ranks as the most important lepidopteran pest in South Africa. European Plant Protection Organisation (EPPO) (1981) classified this pest as belonging to animal kingdom in class insecta in the order of lepidoptera and has common names such as Hübner, Heliothis, Old World (African) bollworm and New World or American bollworm. In South Africa, H. armigera is known as the American bollworm (Pena et al. 2002). Its life cycle consists of four stages namely eggs, larvae, pupa and adult. Caterpillars pass through four developmental instars and ultimately reach 30 to 40 mm in length and have stripes and short black hairs along the length of the body (, 2010).
Under South African weather conditions, H. armigera oviposition period is 10 to 23 days, with an average of 730 eggs per female (Cabi, 1996). Hairy surfaces are preferred for oviposition which is closely linked with the period of bud burst and flower production in most host plants. Eggs hatch in three days at 22.5ºC and nine days at 17.0ºC and the larval period lasts 18 days at 22.5ºC and 51 days at 17.5ºC. The Data Sheets of the EPPO (1981) on Quarantine Pests asserted that the rate of development of the larva is also affected by food availability and fully grown larvae leave the plant to pupate in the soil at a depth of 3 to 15 cm. In Southern Africa, the minimum pupal period in summer is 12 days, increasing as the temperature fall to about 57 days. Emerging female moths must feed before their ovarioles are mature. The average life span for females and males in South Africa is 9 and 14 days respectively.

 Helicoverpa armigera damage and its economic impact on crop production

The infestations of this pest occur regularly throughout the growing season. The insect pest outbreaks occur during the active growth of host plants, mainly from spring through to summer into autumn. Gerber (2007) confirmed that the peak infestations of H. armigera in South Africa takes place during the months of September to November with a second peak in February and March depending on weather conditions. This pest is ubiquitous throughout South Africa, affecting a range of crops. Its larvae may cause damage to citrus blossoms, fruitlets, and young growing tips even on fruit buds. Aslam et al. (2004) indicated that H. armigera destructive activities on fruiting parts of the crop result in 20% to 60% decrease in market value of the crop. Citrus trees are one of the most vulnerable hosts that are attacked by H. armigera. The direct damage to flowers and fruiting structures by larvae cause great losses in most crops. Damage appears as tiny holes in flower buds or petals, leaves and fruit. According to Kaiser and Sheard (2001), the best known damage is on growing tips of the young trees where bollworms make holes into the tips and tunnel through the tightly folded young leaves, where they may be found. Venette et al. (2003) supported this statement and further stipulated that damage caused by the larvae can result in secondary problems such as rotting and ultimately complete plant loss. These authors go on to say that huge loss of agricultural crops can result if infestations get out of hand in crop production.
EPPO (1981) stipulated that an outbreak of H. armigera occurred on young Pinus radiata in New Zealand in 1969 to 1970 when the larvae consumed more than 50% foliage of about 60% trees. Braun (1997) also agreed that this pest can cause 20 to 50% yield loss in cotton. In 2007, Mosinkie declared that H. armigera is estimated to cause yield losses of 15 to 30% on citrus. Sharma (2001) was in accord with this notion and confirmed that this pest caused an estimated loss of over US$2 billion annually in the semi arid tropics despite US$500 million worth of pesticides applied for controlling this pest. Koul et al. (2004) also reported that in China, Bacillus thuringiensis cotton was approved for commercial release in 1997 due to a sharp reduction in cotton production caused by losses and control associated with cotton bollworm, H. armigera. To mitigate the risk of yield losses due to H. armigera activities, South African farmers especially farmers in the Kat river valley of the Eastern Cape midlands spray chlorpyrifos pesticide onto orange trees to suppress its population.

Helicoverpa armigera resistance to pesticides

Horne and Page (2008) testified that H. armigera in the Australian agriculture was found to be resistant to many pesticides. These authors assigned the resistance to regular use of broad spectrum pesticides. Sharma (2001), as cited by Koul et al. (2004), reported that resistance to pyrethroid insecticide caused H. armigera to become one of the economically damaging pests in Indian agriculture. Moore et al. (2004) also revealed that, poor results were obtained from parathion application at Paksaam farm which is situated in the Gamtoos river valley in the Eastern Cape Province where citrus oranges were sprayed with parathion to control H. armigera population. The poor results obtained from such experiment were assigned on the lateness of parathion application.

Facts about chlorpyrifos

EPA (2002) described chlorpyrifos as an organophosphate insecticide, acaricide, and miticide used to control foliage and soil borne insect pests on a variety of food and feed crops. Cremlyn (1991) agreed that chlorpyrifos is a very valuable contact insecticide with a wide spectrum of activity such as by contact, ingestion and vapour action. It is an organo-phosphorous insecticide and its chemical name is 0, 0-diethyl 0-(3, 5, 6-trichloro2pyridyl) phosphorothioate (Watterson, 1998). The chemical formula for chlorpyrifos is C9H11Cl3NO3PS and its synonym name is chlorpyrifos-ethyl (Plate 2.1). It has an oral rat LD50 which ranges from 95 to 270 mg/kg (Kidd and James, 1991). Chlorpyrifos is registered for the control of cutworms, cockroaches, grubs, flea beetles, flies, termites, fire ants, mosquitoes and lice. It is used as an insecticide on grain, cotton, fruit, nut and vegetable crops as well as on lawns and ornamental plants.

Table of contents
Declaration of originality
Table of contents
List of figures
List of tables
List of plates
List of appendices
1.1 Citrus production in South Africa
1.2 Citrus varieties and export in South Africa
1.3 Pesticide usage in citrus production
1.4 Pesticide management in South Africa
1.5 Identified gaps in Act 36 of 1947
1.6 Role played by South African organisations to promote safe use of pesticides
1.7 Study hypothesis
1.8 Study objectives
1.9 Study area
1.10 Study motivation and rationale
1.11 Problem statement
1.12 Structure of the study
2.1 Citrus origin and its production
2.2 Taxonomy of citrus (Citrus spp.)
2.3 Citrus sinensis
2.4 Navel oranges
2.5 The importance of navel oranges
2.6  Citrus pests
2.7 The Helicoverpa armigera
2.8 Helicoverpa armigera damage and its economic impact on crop production
2.9 Helicoverpa armigera resistance to pesticides
2.10 Facts about chlorpyrifos
2.11 Chlorpyrifos residue on citrus fruit
2.12 Chlorpyrifos usage in the Eastern Cape midlands
2.13 Pesticide operators and pesticide usage
2.14 Promotion of judicious use of pesticides in the Western and Eastern Cape Province
CHAPTER 3 PART A – GENERAL MATERIALS AND METHODS ; Experiments on the impact of chlorpyrifos on the larvae of H. armigera on oranges
3.1 Introduction
3.2 Orchard selection
3.3 Sampling and tagging of orange trees
3.4 Scouting for H. armigera larvae
3.5 H. armigera damage to leaves and orange fruitlets
3.6 Spray equipments
3.7 Mixing of chlorpyrifos
3.8 Pesticide spillage during pesticide mixing
3.9 Method of orchard spraying
3.10 Inspection of mature oranges for H. armigera damage
PART B – GENERAL MATERIALS AND METHODS Questionnaire survey on the health status of farm workers
3.11. Introduction
3.12  Request to access private information
3.13  Consent forms
3.14 Sample size
3.15 Questionnaires
3.16 Testing of questionnaires
3.17  Completion of questionnaires by respondents
3.18 Interviews with health professionals
3.19 Farm workers‟ health records
3.20 Coding of questionnaires for statistical analysis
4. Introduction
4.1 Effect of chlorpyrifos on H. armigera population
4.2 Effect of H. armigera population on oranges
4.3 Questionnaire data analysis
4.4 Face to face interviews with health professionals
4.5 Observation  of pesticide personnels‟ actions during a chlorpyrifos spray operation
4.6 Farm workers‟ health records
5. Introduction
5.1 Chlorpyrifos effectiveness
5.2 Orange yields
5.3 Health of pesticide operators
5.4 Conclusions


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