Efficacy of Organic and Synthetic Insecticides on the Control of Cotton Pests: the Bollworm Complex, Helicoverpa Armigera, Dipar

Efficacy of organic and synthetic insecticides on the control of cotton pests: The bollworm complex, Helicoverpa armigera, Diparopsis castanea, Earias insulana (Noctuidae) and the leafhopper, Jacobiella fascialis (Cicadellidae), for small-scale farmers

By Lawrence Nkosikhona Malinga

A thesis submitted in fulfilment of the requirements for the degree of Master of Science (Entomology)

Faculty of Science and Agriculture Department of Zoology and Entomology University of Fort Hare Alice 5700

Supervisor: Prof. Samuel Waladde

Co-supervisors: Dr Emmanuel Do Linh San Mr Eugen Eulitz

August 2012

DECLARATION

This is to declare that this thesis entitled “Efficacy of organic and synthetic insecticides on the control of cotton pests: The bollworm complex, Helicoverpa armigera, Diparopsis castanea, Earias insulana (Noctuidae) and the leafhopper, Jacobiella fascialis (Cicadellidae), for small-scale farmers” is my own work and has not been previously submitted to any institute.

I know that plagiarism means taking and using the ideas, writings, works or inventions of another as if they were ones own. I know that plagiarism not only includes verbatim copying, but also extensive use of another person’s ideas without proper acknowledgment (which sometimes includes the use of quotation marks). I know that plagiarism covers this sort of use of material found in textual sources (e.g. books, journal articles and scientific reports) and from the Internet.

I acknowledge and understand that plagiarism is wrong.

I understand that my research must be accurately referenced. I have followed the academic rules and conventions concerning referencing, citation and the use of quotations.

I have not allowed, nor will I in the future allow, anyone to copy my work with the intention of passing it off as their own work.

Signature of author: ...... Date: ......

Signature of supervisor: ...... Date: ......

ACKNOWLEDGEMENTS

My sincere gratitude goes to my supervisor Prof. Samuel Waladde for his tireless efforts, valuable criticism and support during the writing of this work. I also would like to thank my first co-supervisor, Mr. Eugen Eulitz, for his teaching and guidance during the practical work. My thanks also go to my second co-supervisor, Dr. Emmanuel Do Linh San, for being there for me in such a short notice.

I want to thank Dr. Graham Thompson, Dr. Gerrit Prinsloo and Ms. Jennie van Biljon for their constant support. I also would like to thank the staff at ARC Biometry Unit for their assistance with the analysis of the data, as well as Prof. Johnnie Van Den Berg for his precious advice regarding the use of economic threshold levels.

I would like to express my deepest gratitude to my dearest wife Thobile Lorraine, my handsome son Unathi Stanley (Minime) and my lovely daughter Nomathemba Laurencia for their undying love, support and patience throughout the years.

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ABSTRACT

A research was conducted on cotton to test different plant extracts with potential insecticidal properties against bollworms (Noctuidae) and leafhoppers (Cicadellidae) for the use by small-scale, cotton farmers. The study was carried out during the 2006/07 and 2007/08 seasons at ARC Institute for Industrial Crops, Rustenburg (25°39.0 S, 27°14.4 E) in the North West Province of South Africa. Four organic insecticides, tobacco (Nicotiana tabacium), khaki weed (Tagetes minuta), thorn apple (Datura stramonium) and garlic (Allium sativum) were compared with two chemical treatments, Mospilan® (acetamiprid) and Decis® (deltamethrin), and an untreated control. The cultivar, DeltaOPAL, was planted and the trial conducted using standard practices. Overall, Decis® and tobacco treatments exhibited significantly less bollworm larvae than the other treatments. Tobacco was the most promising biological pesticide against American bollworm (Helicoverpa armigera) and spiny bollworm (Earias insulana) larvae. All the treatments were significantly effective against the red bollworm (Diparopsis castanea) larvae, but Decis® and Mospilan® provided the best control. Although khaki weed, garlic and thorn apple were promising biological pesticides against the bollworm complex, tobacco was the most effective organic treatment. Mospilan® seemed to be more effective on the control of leafhoppers (Jacobiella fascialis), followed by Decis® and tobacco. Among the plant extracts, tobacco and garlic gave higher seed cotton yields compared to the khaki weed and thorn apple during both study seasons. In 2006/07, none of the treatments reached the corresponding economic threshold levels (ETLs). In contrast, in 2007/08, only rarely were the treatments (mostly Decis® and Mospilan®) below the corresponding ETLs. These differences were attributed to the higher rainfall recorded during the 2007/08 season, which reduced the effectiveness of the treatments by partly washing away the pesticidal applications. In addition, a high weed infestation also created competition for nutrients in the soil, thus resulting in lower (0.50-1.25 ton/ha in 2007/08 vs 2.50-5.00 ton/ha in 2006/07), but acceptable cotton seed yields. In conclusion, it is suggested that some plant extracts (particularly from tobacco and garlic) can be used as a cheaper and more environment-friendly alternative to chemical insecticides for the control of bollworms and leafhoppers, although it has been demonstrated that their efficacy do not reach the one of chemical treatments. Further research in the near future is recommended.

TABLE OF CONTENTS

DECLARATION ...... i

ACKNOWLEDGEMENTS ...... ii

ABSTRACT ...... iii

TABLE OF CONTENTS ...... iv

LIST OF FIGURES ...... vii

LIST OF TABLES ...... viii

CHAPTER 1: INTRODUCTION ...... 1

CHAPTER 2: LITERATURE REVIEW ...... 3

Introduction ...... 3

2.1 American bollworm ...... 4

2.1.1 Crop damage and economic importance ...... 5

2.2 Red bollworm ...... 6

2.2.1 Crop damage and economic importance ...... 6

2.3 Spiny bollworm ...... 6

2.3.1 Crop damage and economic importance ...... 9

2.4 Management of the bollworm complex ...... 10

2.4.1 Chemical control ...... 11

2.4.1.1 Synthetic chemical insecticides ...... 11

2.4.1.2 Botanical pesticides ...... 11

2.4.2 Biological control ...... 12

2.4.2.1 Parasitoids ...... 12

2.4.2.2 Predators ...... 14

Predatory bug ...... 14

Spiders ...... 15

Lacewings ...... 15

2.4.2.3 Pathogens and biopesticides ...... 16

2.4.2.4 Bt cotton ...... 16

2.4.3 Cultural control ...... 18

2.4.3.1 Pheromones and traps ...... 18

2.4.3.2 Agronomic techniques ...... 19

2.4.3.3 Crop rotation ...... 19

2.4.3.4 Scouting ...... 20

2.4.3.5 Intercropping ...... 20

2.5 Leafhoppers (Jassids) ...... 21

2.5.1 Life cycle ...... 22

2.5.2 Crop damage and economic importance ...... 22

2.5.3 Control and management of leafhoppers ...... 23

2.5.3.1 Chemical control ...... 23

2.5.3.2 Biological control ...... 25

2.5.3.3 Cultural control ...... 26

2.6 Locally available plants with pesticidal potential ...... 26

2.6.1 Tobacco ...... 26

2.6.1.1 Biological activity of tobacco against insect pests ...... 26

2.6.2 Thorn apple ...... 28

2.6.2.1 Biological activity of thorn apple against insect pests .... 28

2.6.3 Khaki weed ...... 29

2.6.3.1 Biological activity of khaki weed against insect pests .... 29

2.6.4 Garlic ...... 30

2.6.4.1 Biological activity of garlic against insect pests ...... 31

CHAPTER 3: MATERIALS AND METHODS ...... 33

3.1 Field experiment ...... 33

3.2 Trial layout ...... 33

3.3 Land preparation, planting and weed control ...... 34

3.4 Treatments ...... 35

3.4.1 Preparation of plant extracts and synthetic insecticides ...... 36

3.4.1.1 Tobacco ...... 36

3.4.1.2 Khaki weed ...... 36

3.4.1.3 Thorn apple ...... 36

3.4.1.4 Garlic ...... 36

3.4.1.5 Mospilan® ...... 37

3.4.1.6 Decis® ...... 37

3.5 Spray application ...... 37

3.6 Insect scouting and damage rating ...... 38

3.7 Cotton seed yields at harvest ...... 38

3.8 Statistical procedures ...... 39

CHAPTER 4: RESULTS AND DISCUSSION ...... 42

4.1 American bollworms ...... 42

4.2 Red bollworms ...... 46

4.3 Spiny bollworms ...... 48

4.4 Bollworm complex ...... 51

4.5 Analysis of variance ...... 58

4.6 Leafhopper damage ...... 60

4.7 Seed cotton yield ...... 66

CHAPTER 5: CONCLUSION AND RECOMMENDATIONS ...... 69

5.1 Conclusion ...... 69

5.2 Recommendations ...... 73

REFERENCES ...... 74

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LIST OF FIGURES

Fig. 3.1 Trial layout at Rustenburg for the 2006/07 season ...... 33 Fig. 3.2 Trial layout at Rustenburg for the 2007/08 season ...... 34 Fig. 3.3 Planting using a four-row planter at Rustenburg ...... 35 Fig. 3.4 Different levels of leafhopper damage on cotton ...... 40 Fig. 3.5 Scouting form for recording larvae of the bollworm complex ...... 41 Fig. 3.6 Rating form for leafhopper damage ...... 41 Fig. 4.1 Damage and excrement on the cotton boll that was caused by a spiny bollworm larva ...... 50 Fig. 4.2 Seasonal dynamics of different bollworm larvae at different time intervals after application of different insecticides during 2006/07 season ...... 57 Fig. 4.3 Seasonal dynamics of different bollworm larvae at different time intervals after application of different insecticides during 2007/08 season ...... 57 Fig. 4.4 Fitted linear regression on the median damage rating over time that indicates a change rate per week during 2006/07 season ...... 61 Fig. 4.5 The total frequencies R x C contingency table occurrences for Treatment x Rating indicating interaction patterns between treatments and rating classes during the 2006/07 season ...... 61 Fig. 4.6 Leafhopper damage on cotton treated with Decis® and the untreated control at 15 weeks after planting ...... 62 Fig. 4.7 Fitted linear regression on the median damage rating over time that indicates a change rate per week during 2007/08 season ...... 64 Fig. 4.8 The total frequencies R x C contingency table occurrences for Treatment x Rating indicating interaction patterns between treatments and rating classes during the 2007/08 season ...... 64 Fig. 4.9 Leafhopper damage on cotton treated with Mospilan® compared to the untreated control ...... 65 Fig. 4.10 Leafhopper damage on a cotton leaf from the untreated control plot ...... 65

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LIST OF TABLES

Table 4.1 The mean overall number of American bollworm larvae after treatment with different extracts and insecticides on cotton at Rustenburg during the 2006/07 and 2007/08 seasons ...... 45 Table 4.2 The mean overall number of red bollworm larvae after treatment with different plant extracts and insecticides on cotton at Rustenburg during the 2006/07 and 2007/08 seasons ...... 47 Table 4.3 The mean overall number of spiny bollworm larvae after treatment with different extracts and insecticides on cotton at Rustenburg during the 2006/07 and 2007/08 seasons ...... 49 Table 4.4 The mean overall number of the total bollworm larvae after treatment with different extracts and insecticides on cotton at Rustenburg during the 2006/07 and 2007/08 seasons ...... 53 Table 4.5 Mean overall population of bollworm larvae per 12 plants at different time intervals after application of different extracts and insecticides during the 2006/07 season ...... 53 Table 4.6 Mean overall population of bollworm larvae per 12 plants at different time intervals after application of different extracts and insecticides during the 2007/08 season ...... 54 Table 4.7 Analysis of variance for the total bollworm counts out of 12 plants at Rustenburg during the 2006/07 season ...... 59 Table 4.8 Analysis of variance for the total bollworm counts out of 12 plants at Rustenburg during 2007/08 season ...... 59 Table 4.9 Seed cotton yield in plots treated with different extracts and insecticides at Rustenburg during the 2006/07 and 2007/08 seasons ...... 67

CHAPTER 1: INTRODUCTION

The grain industry is one of the largest in South Africa, producing between 25% and 33% of the country's total gross agricultural production. Cotton constitutes about 74% of natural fibre and 42% of all fibre processed in South Africa (SAinfo, 2008). However, the cotton crop is severely damaged by several pests, which reduce cotton production, especially in the rural sector among the small-scale farmers. Insect pests with different feeding strategies attack cotton early in the cotton-growing season. Cotton seedlings are attacked by leaf-feeders and sucking pests such as leafhoppers. Later on in the growing season, flower feeders and boll feeders such as cotton bollworms become dominant. Numerous cotton pests have developed resistance to commonly used pesticides, and are now difficult to control (Singh and Dhaliwal, 1993). In order to keep pests under control while maintaining good yield levels, farmers are applying large quantities of synthetic fertilizers and pesticides. However, synthetic pesticides have certain negative effects, such as destroying pest natural enemies. Certain synthetic pesticides have insecticidal properties similar to those found among organic insecticides, but they differ from natural compounds in that they do not break down easily and they accumulate in food webs, causing environmental contamination and unforeseen consequences in ecosystems. In spite of these problems, worldwide, pesticides usage is still increasing (Bruinsma, 2003; FAO, 2005). In most developing countries pesticide and other inputs are relatively expensive and increase the overall production costs, which small-scale cotton farmers can hardly afford (Scialabba and Hattam, 2002). In order to minimize intensive pesticide applications, integrated management of cotton pests remains the best option likely to contribute to sustainable cotton production worldwide (Phiri, 2003). Farmers are looking for better-integrated pest management strategies, including environment-friendly pesticides.

More than 160 species of insects have been reported to attack cotton at various stages of its growth as defoliators, tissue borers and sap-suckers, causing yield losses up to 60% (Manjunath, 2004).

Among them, bollworms and leafhoppers are the most destructive, requiring major efforts to save the crop from them. Chemical insecticides are used extensively on cotton for control of insect pests, especially bollworms (Manjunath, 2004). Botanical insecticides have long been known as attractive alternatives to synthetic chemical insecticides for pest management, because botanicals reputedly pose little threat to the environment or to human health. Man has been using natural products of animals, plants and microbial sources for thousands of years, either in the pure forms or crude extracts (Parekh and Chanda, 2007). When pesticides are to be used they must be cost-effective and used in a manner that minimizes the development of pest resistance to pesticides and harm to pest natural enemies. In view of the above-mentioned problems, there is a need to provide resource-poor farmers with cost-effective pest-control measures using resources that are readily available. The objectives of this project were as follows: i. Find ways of using locally available resources to lower costs for pest control, while at the same time improving yields and profit margin for the small-scale cotton farmers in rural areas. ii. Use locally available plants such as tobacco (Nicotiana tabacum), khaki weed (Tagetes minuta), thorn apple (Datura stramonium), garlic (Allium sativum), to prepare extracts and test for their biopesticide potential. iii. Apply the extracts on cotton plants and assess their pesticidal effects on the following cotton pests: leafhopper (Jacobiella fascialis), American bollworm (Helicoverpa armigera), red bollworm (Diparopsis castanea) and spiny bollworm (Earias insulana).

The work reported here was based in the field and tests were conducted during the 2006/07 and 2007/08 seasons at the ARC-Institute for Industrial Crops in Rustenburg. At the above study site, the pesticidal effects of plant extracts were compared with the effects of two synthetic chemical insecticides, namely Mospilan® 20 SP Acetamiprid (acetamidine) and Decis® Deltamethrin (pyrethroid).

CHAPTER 2: LITERATURE REVIEW

Introduction

The bollworm complex (American, red and spiny bollworms) (Pearson and Darling, 1958) and leafhoppers (jassids) are some of the major cotton pests around the world. Other pests that are associated with cotton include Aphis gossypii (Glover, 1877), Bemisia tabaci (Gennadius, 1889), Thrips tabaci (Lindeman, 1889) and Tetranychus cinnabarinus (Boisduval, 1867) among others. Plants such as tobacco (Nicotiana tabacum), thorn apple (Datura stramonium), khaki weed (Tagetes minuta) and garlic (Allium sativum) have been identified as plants with a potential for use in pest control (Prakash and Rao, 1997). For example Prabhu et al. (1990) and Patil et al. (2007) reported nicotine sulphate isolated from waste tobacco leaves to show toxicity to American bollworm. However, information on the efficacy of these plant extracts on the control of bollworms and leafhoppers in South Africa is inadequate or non-existent.

This chapter reviews the life cycles and economic importance of these pest species. Pest control and management strategies using chemical, biological and cultural control practices, as well as use of transgenic cotton are also discussed. Finally the biopesticidal potential of plant extracts from tobacco, thorn apple, khaki weed and garlic are also reviewed. These plants have been investigated in the current study because they are locally available and it is expected that they have pesticidal properties that can be put to use in the management of cotton pests by small-scale farmers.

2.1 American bollworm

Helicoverpa armigera (Hübner, 1805) (Lepidoptera: Noctuidae) is commonly known as the American, African or cotton bollworm. It is one of the most polyphagous, highly mobile and cosmopolitan pests attacking more than 100 different commercial crops including cotton, maize, wheat, sorghum, sunflower and tomato. This moth is distributed throughout Africa, the Mediterranean, Asia, Australia and Oceania (Ferris, 2002).

The female starts ovipositing four days after emerging and may lay 1,000 or more eggs over a period of 10 days. The eggs are about 0.5 mm in diameter, spherical and white to pale yellow with a series of ridges or striations when first deposited. Eggs are usually laid singly in young buds, stalks or fruits and they darken to brown or brownish-grey prior to hatching after a 2-4 day incubation period (Bijlmakers, 1989). Newly emerged larvae usually feed on empty eggshells before feeding on the plant (Barber, 1941). Pitre and Hillhouse (1981) reported that small larvae prefer young, nutrient-rich, terminal buds and flowers. Older larvae feed on large buds or young cotton bolls and, if these are not available, older bolls are attacked. On cotton plants the larvae often feed with their heads inside the boll and the rest of their bodies exposed. A single larva can move about on the plant a great deal and can attack 2-3 fruits per night causing serious damage to the cotton crop. On the bean crop, larvae burrow into large pods and eat the developing seeds.

Early larval instars are black and later instars are dark and light brown or green. The body is marked with bilateral alternating dark and white. A mature larva has some hairs on its body but the colour of the caterpillar is so variable that identification may be difficult. The head is brown and the larva is 3-4 cm long when fully grown. When disturbed, the larva raises its head and folds it under its body. If disturbed further, it coils and falls on to the ground. The larva develops through six instars over a period of 14-30 days (King and Coleman, 1989), but this period can last longer depending on temperature (Barteková and Praslička, 2006) and food availability. The fully developed larva moves to the ground, where it pupates.

The bollworm pupa is brown in colour and approximately 2 to 5 cm in length (Sharp, 2010). The pupal stage usually lasts 10-14 days, but it may remain dormant (undergo diapause) for six months during the cold season. When the temperature rises and rain begins, the brown adult moth emerges. The adult is a brown, nocturnal moth with a wing span of about 4 cm (Ghaly and Alkoaik, 2010). Forewing colour varies from dark to yellow brown, occasionally greenish, with the dark spots that often form a V-shaped mark or a line. The hind wing has a dark band with a central light spot, which is useful for distinguishing H. armigera from the closely related budworm, H. punctigera (Ferris, 2002). Although H. armigera is capable of long-distance flight, moths typically do not disperse far from emergence sites (Ferris, 2002). This species has several generations per year and each generation lasts about 32-40 days.

2.1.1 Crop damage and economic importance Larsen (2005) reported that H. armigera is present in all the cotton-production regions of South Africa. It can reach population levels which cause serious crop damage. The larvae tend to move from boll to boll and the damage they cause may be disproportionate to their numbers (Arora et al., 2009). This pest can attack several genera of commercially important plants, which include cotton, maize and sorghum as primary host plants. Secondary host plants include tomatoes, tobacco, legumes, vegetables and sunflower. In India, Ganguli (2003) estimated loss due to H. armigera to be around $500 million annually, while Krishnappa et al. (2005) reported that by 2005 the pest caused crop damage worth about $1 billion per annum. Since the end of the 1980s, cotton production has decreased in China owing to a decline in both yield and coverage area. The decline in yield of 15 to 30% has mainly been caused by bollworm infestation. Zhang and Zhang (1998) reported that in 1992 and 1993, outbreaks of cotton bollworm infestation in China caused direct economic losses of about $630 million. This pest discouraged farmers from growing cotton. As a result, the national production area decreased by 10-15%, and there was a tendency for cotton production moving from relatively favourable areas towards marginal regions where pest infestations were not very intensive.

2.2 Red bollworm

The red bollworm, Diparopsis castanea (Hampton, 1902), is a lepidopteran also belonging to the family Noctuidae. Eggs of this moth are very small, slightly elongated, and laid under the calyx of green bolls. The first instar larvae are tiny, white caterpillars with dark brown heads. Later instars develop to 1.2 cm and bear large transverse red stripes on their backs. The moth spends most of its larval life inside the cotton boll and so it is difficult to control with insecticides (Campion, 1967). A fully developed larva grows to 2-3 cm long and assumes a red coloration before pupating. The larva undergoes pupation and the adult emerges in approximately 17 days. The moth is small, greyish-brown, inconspicuous and has a 3 cm wingspan with olive green markings. The wing tips are conspicuously fringed and when they are folded, the moths have an elongated slender appearance (Godfrey et al., 2008).

2.2.1 Crop damage and economic importance Red bollworms damage cotton squares (flowers) and bolls, the damage to bolls being the most serious. Diparopsis castanea larvae are seed feeders. They burrow into the bolls, cut through the lint in order to reach the seeds. As the larva burrows within a boll, the lint is damaged and stained, resulting in severe quality loss. Under dry conditions, yield and quality losses are directly related to the percentage of bolls infested and the number of larvae per boll. Under high humidity conditions, it takes one or two larvae to destroy an entire boll, because damaged bolls are vulnerable to infection by boll rot fungi

(Godfrey et al., 2008).

2.3 Spiny bollworm Earias insulana (Boisduval, 1833), commonly known as spiny bollworm in the cotton industry, is also a lepidopteran belonging to the family Noctuidae. Spiny bollworm and pink bollworm, Pectinophora gossypiella (Saunders, 1843), have been observed to cause considerable economic loss.

Whereas pink bollworm is still considered to be among the most important worldwide cotton pests, the spiny bollworm is found particularly in Asian and African countries (Kiray, 1964; Stam and Al-Mosa, 1990). The larvae of both pests overwinter in mature cotton bolls and trash left in the soil after harvest (Bariola et al., 1987; Ünlü, 2001). Therefore, these bolls are a very important source of primary infestation.

The eggs are light blue-green, roughly spherical and slightly under 0.5 mm in diameter. Ridges alternately project upwards to form a crown and the egg loosely resembles a poppy head or pomegranate (Pearson and Darling, 1958). Eggs are laid singly and on most parts of the plant, although the leaf lamina is little used (Pearson and Darling, 1958). On cotton the favoured oviposition sites are the young shoots, peduncles and bracteoles or flower buds and apex of the bolls (Bacheler and Mott, 2009). The egg stage incubates for 5-10 days (Assem et al., 1974) and the larva that emerges develops to 13-18 mm long and 2.5-3 mm wide (Gardner, 1947). After hatching, the larvae may move some distance before settling down to feed (Pearson and Darling, 1958). There are normally five larval instars that are usually moulting within the tunnel as it develops. The entire larval stage may last 8-25 days (Assem et al., 1974).

The larva is stout and spindle shaped, tapering after the fifth abdominal segment. The larval body chaetotaxy of E. insulana differentiates it from other species of noctuids such as Earias spp. (Singh, 1987; Singh et al., 2003). Body colour is variable but is generally suffused with darker brown or black spots. It may also be greyish-brown, through grey to green, with a distinctly paler or white median line. When the larva is ready to pupate on the cotton plant, it spins a cocoon often between the boll wall and the bracteoles or the cocoon may be attached to a twig or withered leaf, or among surface debris on the soil. On okra, pupation may occasionally take place within the pod (Assem et al., 1974).

The pupa is about 13 mm long and yellow to chocolate-brown or purplish- brown in colour, with a smooth or slightly ridged surface. It is bluntly rounded at each end with three small projections on the terminal segments. It is enclosed in a cocoon shaped like an inverted boat, spun from a tough, felt- like, dirty white or pale brown silk. Cocoons may be attached to the food plant, to plant debris on the ground, or to crevices up to 30 cm deep in the soil (Pearson and Darling, 1958). In India, Deshpande and Nadkarny (1936) observed that pupation invariably occurs in the soil, with the pupa attached to clods of earth in cracks and crevices 10-30 cm below the ground surface. The pupal stage usually lasts 9-15 days (Assem et al., 1974), but may extend to 2 months in areas where the temperature drops and the pupa becomes dormant without actually undergoing proper diapause (Pearson and Darling, 1958).

The adult is a small moth with green or yellowish-green wings, pale hind wings, and a wingspan of 12-20 mm. It is covered with a soft, fairly dense coating of scales. The abdomen and hind wings are a plain silvery or creamy white colour. Pearson and Darling (1958) and Couilloud (1983) noted that the colour variation of the adult is seasonal and triggered by environmental factors.

The length of the life cycle of E. insulana depends on the temperature and thus varies with the seasons. There is no true diapause, though development is retarded in cold weather. This species tolerates a wide variety of climatic conditions, though it does not adapt well to damp conditions. The imagos show seasonal colour polymorphism, which appears to be determined by climate acting on the pupal stage. A typical form occurs with optimum temperature and humidity; colour variations occur when the conditions vary from optimum (Couilloud, 1983). The most favourable conditions for rapid multiplication are warm, but not excessively hot, weather, cloudiness, frequent light rain and relative humidity of 65-85% (Katiyar, 1982).

Kehat and Gordon (1977) studied the mating behaviour of E. insulana in the laboratory. Females mate on the second night after emergence when they assume a characteristic calling posture, which exposes the glandular tissue, releasing a pheromone attractive to the males (Tamhankar, 1995). They may mate more than once a night, and several times after oviposition begins. However, a single spermatophore is sufficient for their entire egg production. Males mate only once a night, but several times during their lifespan (Kehat and Gordon, 1977). Fecundity appears to be greater in adults that mate early in life (Rashad et al., 1992). The pre-oviposition period generally lasts 3-7 days, but may go up to 9 days in unmated females. Each female can lay 5- 150 eggs depending on the conditions. Females can live for 4-13 days, while males live for 2-20 days (Assem et al., 1974). Tamhankar (1995) noted that the availability of a suitable food source enhanced mating and oviposition behaviour.

2.3.1 Crop damage and economic importance Spiny bollworms affect the cotton plant during the vegetative, flowering and fruiting stages. The affected parts are the leaves, stems, growing points and fruit. The symptoms of attack are similar for all Earias spp. Cotton infestation generally starts with shoot boring in the young crop. Earias insulana enters the terminal bud of the vegetative shoot and channels downwards from the growing point, or directly penetrates the internodes. Only soft, growing tissue is attacked. Extensive tunnelling results in wilting of the top leaves and the collapse of the apex of the main stem. The whole apex turns blackish-brown and dies. If only the apical bud is attacked, the damage may not be noticed until the main stem divides when the axilllary buds take over growth (Kashyap and Verma, 1987; Reed, 1994). As the buds and flowers appear they wither and are shed; they usually have a conspicuous hole where the larva has entered. The shedding of minute buds is often blamed on mirids but may be caused by very young Earias (Pearson and Darling, 1958). The bolls are also attacked, but only when they are unripe.

Older larvae feed on flower buds (squares) and green bolls of various ages. The bracteoles of damaged flower buds open out, causing the condition known as “flared squares”. The caterpillar’s entrance hole in a bud or boll is neat and circular and may be blocked with excrement produced by the feeding larva, which usually bore deeply. The tunnel often enters the bolls from below, at a slight angle to the peduncle (Pearson and Darling, 1958). Small bolls, up to 1-week old, turn brown, rot and drop. Larger bolls that are 2- 4 weeks old may not drop but open prematurely and may be so badly damaged that they cannot be harvested. Bolls are vulnerable up to 6 weeks of age (Butani, 1976). As a result a severe attack of E. insulana causes extensive shedding of flower buds and reduced yield. Secondary invasion by fungi and bacteria may conceal the infestation by the spiny bollworm. Earias spp. can transmit Xanthomonas malvacearum, causing bacterial blight of cotton (Borker et al., 1980). The spiny bollworm has also been reported to transmit the black fungus infection (caused by Rhizopus nigricans) in cotton crops (Nasr and Azab, 1969).

2.4 Management of the bollworm complex

A wide range of tactics are used in the pest management of the bollworm complex. The choice depends on the applicable tactics in the area. Usually, when high population levels of the bollworm occur, the objectives of management are to keep infestations below damaging levels in any given season without creating secondary outbreaks of other pests, and to reduce the overwintering population that will threaten crop in the following season. The main control tools are sensible use of insecticides, timely crop termination and harvesting, rapid crop destruction and properly timed irrigations. Because of the danger of secondary outbreaks it is wise to limit insecticide treatments to those periods when susceptible bolls are present and when sampling shows that the percentage of infested bolls is above the treatment threshold (Godfrey et al., 2008).

2.4.1 Chemical control

2.4.1.1 Synthetic chemical insecticides Cotton bollworms can be controlled using selective and non-selective chemical insecticides. Selective insecticides are preferable because natural enemies are not badly affected. The use of non-selective insecticides just prior to the bollworm flight should be avoided in both conventional and Bt cottons (see 2.4.2.4) because their use destroys predacious arthropods and this can result in more crop damage even with more intensive spraying for bollworm control (Turnipseed and Sullivan, 1999). The intensive and injudicious pesticide sprayings enhance the detoxification capabilities of pest populations (Rajendran, 2000). It is therefore preferable to apply a pest management strategy which uses a judicious blend of chemical and biological tactics. In India, synthetic pyrethroid insecticides were employed to fight against ever-increasing number of insect pests in cotton systems from time to time (Rajendran, 2000). However, the early use of synthetic pyrethroid like cypermethrin and decamethrin was found to increase secondary pests such as aphids and whiteflies.

Application of pyrethroid insecticides, unless very much warranted should be strictly avoided, for fear of pest resistance development to this group of chemical insecticides which also have the propensity of destroying several types of natural enemies. Insecticides are needed only if the population exceeds the treatment threshold, especially when the crop has a significant number of flower buds or green bolls which require maximum protection to develop into mature bolls (UC IPM, 1996).

2.4.1.2 Botanical pesticides There has been tremendous progress in the development of various commercial formulations of botanical insecticides such as that obtained from neem oil, Azadiracta indica. Various botanical insecticides prepared from neem oil are readily available in the market. These insecticides are preferred over the more potent insecticides because they are eco-friendly, and they do

12 not have negative effect on the occurrence of natural enemy species in the crop environment (Rajendran, 2000).

Syringa, Melia azedarach, extracts have been found to have potential for the control of H. armigera (Van den Berg and Charleston, 2003). However, lepidopterans such as H. armigera are generally less sensitive to the feeding- deterrent effects of botanical pesticides (Ma et al., 2000).

2.4.2 Biological control In biological control, pest suppression is achieved by facilitating the build up of large numbers of pest natural enemies (parasitoids, predators and pathogens) in the cotton crop. The principle behind biological pest control is that a given pest has enemies – predators, parasites or pathogens. By introducing or encouraging such enemies, the population of pest organisms can decline. When natural enemies are abundant in the cotton field, pest levels can be tolerated for long periods without pesticide use, which means there is saving on pest control costs.

2.4.2.1 Parasitoids Some of the most important naturally occurring parasitoids on cotton bollworms include Trichogramma chilonis (Ishii, 1941), Chelonus curvimaculatus (Cameron, 1906), Rogas aligarhensis (Quardi), Eucarcelia illota (Curran, 1927), and Campoletis chloridae (Uchida, 1957). Trichogramma chilonis is a polyphagous egg parasite that has been successfully used in Pakistan against lepidopterous insect pests (Zubair et al., 2007). Since it attacks the egg stage, damage done by larvae is avoided. According to the Indian National Bureau of Agriculturally Important Insects (2008), the major pests against which Trichogramma chilonis has been used or recorded include cotton bollworms Earias vittella, E. insulana, and Helicoverpa armigera. According to Broodryk (1969) and Rechav (1978), Chelonus species, egg-larval parasitoids of lepidopterans, characteristically have high fecundity rates. This is an important asset for a biocontrol agent.

An ichneumonid parasitoid, Campoletis chloridae is reported to attack H. armigera larvae (Chandel et al., 2005). Gupta et al. (2008) conducted laboratory and field studies to gain new understanding of the biology and biocontrol potential of C. chloridae on H. armigera. The authors released 1-2 day old C. chloridae at the rate of 15,000 adults/ha in chickpea. They recorded increase in parasitism after 7 and 14 days of parasitoid release; there was an overall reduction in the H. armigera population. Furthermore, their results showed a reduction in pod damage and chickpea yield improved. According to Dhillon and Sharma (2007), under natural conditions, H. armigera is the most preferred host of C. chloridae on a number of crops, such as cotton.

The occurrence of chrysopids on cotton in relation to H. armigera was studied in Tanzania by Kabissa et al. (1996) between 1988 and 1991. Among the chrysopid species observed on cotton, only Mallada desjardinsi and Chrysoperla sp. occurred on cotton when H. armigera was present. Peak abundance of eggs and larvae of H. armigera occurred between the 8th and 13th weeks. Parasitism in populations of field collected larval, pupal and imaginal chrysopids was noted. Activity of adult H. armigera and chrysopids monitored by light traps showed two peaks of abundance coinciding with short and long rains. Parasitoid behaviour and efficacy in biological control programs is strongly influenced by semiochemicals (Tumlinson, 1988). The goals of using semiochemicals in pest management are (1) to monitor pest populations to determine if control is warranted and (2) to alter the behavior of the pest or its enemies to the detriment of the pest (Byers, 2005). Among entomophagous insects, Trichogramma spp. have received considerable attention, due mainly to their potential as biological control agents against lepidopteran crop pests (Boo and Yang, 1999). Trichogramma pretiosum, for example, is a candidate for inundative release against Heliothis spp. (King et al., 1986; King and Coleman, 1989). Trichogramma species use various semiochemicals including plant synomones and host kairomones in their search for host eggs (Noldus, 1989a, b). Volatile chemicals emanating from female moths mediate increased rates of parasitism (Lewis et al., 1982).

Laboratory olfactometer experiments confirmed behavioral response of T. pretiosum to the odour of calling H. zea moths (Noldus, 1988).

Boo and Yang (1999) conducted a study on chemically mediated interactions between an egg parasitoid, Trichogramma chilonis, and its host insect, Helicoverpa assulta. They reported that T. chilonis was attracted to the sex pheromone of H. assulta. Furthermore, they revealed that H. assulta eggs were more parasitized by T. chilonis when the eggs were treated with male moth scale extract of H. assulta. Parasitism was also affected by the age of the parasitoid, time of day, and moth scale extract concentration. Naturally occurring native predators such as hymenopterous and tachinid parasitoids like Eriborus argenteopilosus, Microchelonus spp., Palexorista laxa, Carcelio illota and Goniopthalmus halli are also common on H. armigera.

2.4.2.2 Predators Release of arthropod predators holds promise for suppressing herbivorous insect populations in commercial crops, but dispersal from release sites remains a practical issue that can limit their impact (Neves et al., 2008). Ursula et al. (1996) reported that cotton plants attacked by herbivorous insects release volatile semiochemicals that attract natural enemies of the herbivores to the damaged plants.

Predatory bug Eocanthecona furcellata Wolff (Hemiptera: Pentatomidae) could be regarded as a potential larval predator for the whole cotton-growing season. The predatory stinkbug is found especially in cotton, chickpea and vegetable fields and has been found preying on larvae of leaf worm, spotted bollworm and American bollworm in Myanmar (Gillham, 1980; Nu and Win, 2000; Khin, 2001). Nyunt and Vidal (2007) conducted experiments on potential biological control of bollworms larvae using E. furcellata in Southeast Asia and reported that adults of the bug preferred to prey on H. armigera larvae reared on cotton plants. Based on their results they recommend that E. furcellata can be released in cotton fields as a biocontrol agent of H. armigera.

Spiders Spiders are predators of cotton sucking pests including the bollworms egg, nymph and adult. Spiders are prominent natural enemies that attack cotton pests (Van den Berg and Dippenaar-Schoeman, 1991). Spiders cannot control major pest outbreaks by themselves but they can play a key role in keeping pest species at low densities early in the season and between peaks of pest species activity. Therefore spiders can play an important role in keeping pests at low levels and preventing outbreaks (Dippenaar-Schoeman et al., 1999). Predation is not limited to adult insects but includes the egg and larval or nymphal stages as well (Whitcomb, 1974; Nyffeler et al., 1990). Dippenaar-Schoeman et al. (1999) further mentioned that the major effect of spiders could only be achieved through the combined activities of a variety of species in a given habitat. Spider communities associated with cotton have been widely studied in North America (Whitcomb and Bell, 1964; Leigh and Hunter, 1969; Young and Lockley, 1985; Nyffeler et al., 1987), Australia (Bishop and Blood, 1977, 1981; Bishop 1979, 1980, 1981), Asia (Wu et al., 1981; Zhao, 1984; Zhao et al., 1989), Zimbabwe (Brettell and Burgess, 1973), and South Africa (Coates, 1974; Van den Berg, 1989; Van den Berg et al., 1990; Van den Berg and Dippenaar-Schoeman, 1991). Dippenaar-Schoeman et al. (1999) recorded 127 species of spiders from five cotton-growing areas in South Africa between 1979 and 1997.

Lacewings Green lacewing, Chrysoperla carnea, larvae (Family Chrysopidae) are active predators that attack several species of aphids, spider mites (especially red mites), thrips, whiteflies, eggs of leafhoppers and moths. A single lacewing larva can consume more than 40 bollworm eggs in one day (Boyd et al., 2004). Mass releases of C. carnea in a Texas cotton field trial reduced bollworm infestation by 96% (Rosenheim and Wilhoit, 1993). Release of C. carnea as a biological control agent, without use of any insecticide was however not successful for control of the spiny boll worm in cotton (Mirmoayedi and Maniee, 2009). In the experiment of integrated pest control, the latter authors found that the use of C. lucasina together with spray of Diazinon was more successful to control spiny bollworms in cotton.

2.4.2.3 Pathogens and biopesticides Nuclear Polyhedrosis Virus (NPV) is the pathogen that causes a natural disease that affects H. armigera larvae. Commercial formulations of Helicoverpa NPV’s are currently available for the control of H. armigera larvae. NPV can kill young larvae within four days of ingestion, older larvae within five to seven days, depending on dose and temperature. NPV is best used against pest populations that are at or near economic threshold. If Helicoverpa population levels are much higher than threshold, the percentage control from NPV may not be enough to reduce the population below threshold. Tang and Hou (1998) reported that the entomopathogenic fungus, Nomuraea rileyi, caused 90.5-100% mortality in fourth-instar larvae of Helicoverpa armigera, when applied at 107 conidia/ml to corn silks. Ingle et al. (2003) stated that under laboratory conditions, N. rileyi at 2×106 spores/ml was highly virulent, resulting in approximately 100.0% mortality of H. armigera.

2.4.2.4 Bt cotton Bacillus thuringiensis is a common rod-shaped bacterium occurring in the soil. It has a wide distribution in the world and is capable of producing ‘cry’ proteins. Because of its capability, it produces one (Cry1Ac) or several (Cry1Ac+Cry2Ab, Cry1Ac+Vip, Cry1Ac+Cry1F) toxins. These proteins are cleaved in the mid-gut of many lepidopteran insects to produce protein subunits that bind to receptors in the insects’ stomach and cause membrane disruption (Chaudhry and Guitchounts, 2003). The ‘cry’ proteins are toxic to certain types of insects, such as the bollworm moth, that attack cotton, and the action is specific to those insects. Bollgard, insect-resistant genetically modified (GM) cotton, suppresses the bollworm, but it is a little more expensive to buy than conventional cotton. Bt gene produces an endotoxin that provides resistance to attack from the bollworm complex (Green et al., 2003). The first transgenic cotton with a Bt gene expressing the protein at economically viable levels was developed in 1989 and USA conducted multi- location field-testing of the Bt cotton in 1990. The use of Bt cotton helps to prevent damage by the cotton bollworm.

Bt cultivars control only caterpillars, not other pest insects, such as thrips, cotton aphids, plant bugs, and stink bugs. Impressive benefits in insecticide use reduction, bollworm control and farmer profitability were reported for Bt in USA, China, Australia and South Africa (Russell, 2003). By 2002, according to James (2003), Bt cotton varieties have been commercialised in nine countries worldwide, including South Africa, where it was introduced in 1998. To reduce the risk that an insect would become resistant to Bt cotton, non-Bt cotton must be planted near Bt cotton to provide “refuges” for susceptible pests. South Africa has quantified the number and importance of natural plant refugia for bollworm. This is an important step towards developing effective resistance- delaying refugia for small-farmer situations (Russell, 2003). Because resistant insects are rare, the only mates they are likely to encounter would be susceptible insects from the refuges. The hybrid offspring of such a mating generally would be susceptible to the toxin. In most pests, offspring are resistant to Bt toxins only if both parents are resistant.

The documented bollworm resistance to Bt cotton was firstly discovered between 2003 and 2006 in Mississippi and Arkansas (Tabashnik et al., 2008). The data documenting bollworm resistance were first collected seven years after Bt cotton was introduced in 1996 (Jensen, 2008). Green et al. (2003) monitored numbers of bollworm larvae at Makhathini flats in Kwazulu-Natal and noted that high numbers of bollworm larvae were present in plant species that served as refuges. They recorded that out of the nine plant species that were scouted, Abutilon austro-africanum and A. sonneratianum appeared to be the preferred alternative host plants of spiny bollworm. Cattaneo et al. (2006) reported that the use of Bt cotton reduces insecticide use and has higher yield than non transgenic cotton for any given number of insecticide applications. Bacheler (2009) reported that in 2008 bollworms caused less damage to bolls on Bollgard and Bollgard II cotton compared to conventional cotton. He stated that, that was the lowest boll damage ever recorded for each of these technologies since their introduction.

Bacheler (2009) further reported that a review and synthesis of the data collected to date and of farmer experiences in North Carolina with Bollgard cotton from 1996 through 2008 suggests that Bollgard cotton, if treated when needed, will usually provide better bollworm control than that provided by insecticides in conventional cotton under most grower circumstances.

2.4.3 Cultural control Cultural methods of controlling the bollworm populations involve light and pheromone traps, cultivation of fields before planting, correct planting dates, removal of the plant stalks, intercropping and crop rotation. Cultural controls, with the exception of the use of Bt cotton and mating disruption, are suitable for use on organically grown cotton.

2.4.3.1 Pheromones and traps Sex pheromones, plant origin insecticides and trap cropping are new approaches to insect control that can be included in the existing pest management practices (Ghewande and Nandagopal, 1997). Sex pheromones have been used in the field for H. armigera and Spodoptera litura (Anonymous, 1986; Pawar et al., 1988). Methods for the use of sex pheromones for control of H. armigera and S. litura were explored in groundnut through the All India Coordinated Project-Groundnut (AICORP-G) (Anonymous, 1986). A mean of 3.9 males of H. armigera were trapped at a height of 1 m and the number trapped decreased with increasing height of the trap (Pawar et al., 1988). Pawar and Srivastava (1988) reported that traps with mixed sex pheromones of S. litura and H. armigera, showed no reduction in the catch of S. litura, but a drastic reduction in the H. armigera catch. In order to monitor bollworm populations in a given area, pheromone and light traps have been used to determine the presence of pest at Makhathini flats (Green, 2004). Light and pheromone trap catches indicated that there could be an influx of moths from the fallow fields or natural bush areas that are close to the cotton fields.

2.4.3.2 Agronomic techniques Ploughing fields exposes harbouring pests in the soil, especially pupae of the bollworm pest complex, to natural mortality factors such as desiccation, birds and ants which feed on the pupae. One of the most important factors determining the planting time for cotton is the soil temperature. Cotton should be planted when a temperature of 16°C or above has be maintained in the soil, hence mid-October to mid-November can be regarded as the best time for planting in South Africa. Lower temperature can result in poor germination, accompanied by low yields and poor fibre quality. In dry land cotton areas like Mpumalanga and Kwazulu-Natal, cotton can already be planted in early October (ARC, 1996).

Growing early maturing varieties enable the cotton bolls to mature before the heavy population of bollworms builds up (Sabesh, 2006-07). Plant spacing also play an important role in cotton production. Rossi and Braojos (2003) conducted a study in Spain on cotton response to three plant population densities and reported that higher plant densities produce a lower number of fruiting and vegetative branches per plant. They further mentioned that the total nodes and the number of bolls per plant also decreased as the density increased. In 1973, Bridge et al. reported that the highest yields from plant populations can be achieved from 70,000 to 121,000 plants per hectare. Babiker (2003) obtained the highest seed cotton yield at 125,000 plants per hectare and thereafter the yield started to decrease. Therefore it is imperative to consider plant spacing when planting cotton.

2.4.3.3 Crop rotation Crop monocultures are often damaged more severely by pests than the same crop located in an area with crop diversity. However, there are cases where such diversity can aggravate pest problems. It is in these situations where trap crops can be important. Crop rotation can be implemented as a cultural control measure as it removes the suitable crop that is the source of food for the bollworm populations.

In India, Singh et al. (2003) conducted a study on rotation of cotton followed by wheat, chickpea, barley, mustard, peas and fallow in winter. They reported that seed cotton yield after rotation was significantly higher in cotton-fallow, cotton-pea and cotton-chickpea than cotton-mustard, cotton-barley and cotton-wheat.

2.4.3.4 Scouting Scouting and field monitoring form the cornerstone of IPM. Field scouting should make the farmer informed of the relative abundance of pests and their natural enemies. Regular, systematic scouting for bollworm eggs and bollworm larvae is essential, particularly when the major moth flights are under way. Plant compensation for boll damage at this time of year is minimal, and caterpillar feeding, especially on bolls, can dramatically reduce yields. According to Bacheler and Mott (2009), when scouting a cotton field for bollworm eggs and small larvae, all major areas in the field must be covered and random inspection of selected terminals, squares, and bolls throughout the field must be conducted. They mentioned that in conventional cotton, bollworm eggs are the primary focus of the scout until the initial insecticide application, although the scout should be alert for and record small larvae. They further advised that when the egg threshold has been met or exceeded and treatment made, the primary scouting focus shifts toward finding small bollworms feeding on squares and bolls, including those in yellow and pink flowers. Weekly scouting leading up to the major bollworm moth flight is usually adequate. As a general rule, Bacheler and Mott (2009) recommended a 4- to 6-day scouting schedule for the remainder of the moth flight, although this schedule may vary according to the moth pressure, the susceptibility of the crop, the insecticide rate used, and the damage risk the farmer is willing to take.

2.4.3.5 Intercropping In many countries, cotton is traditionally intercropped with other plants in order to increase yields and to control pests (Schader et al., 2005). Intercropping also generates an extra income for a farmer who can harvest the crops and sell. Schader et al. (2005) tested the effects of intercropping cotton and basil,

Ocimum basilicum, on pest infestation in Egypt. Basil, which is known for its repellent effect on various insect pests, was mixed with cotton. These authors discovered that compared with the non-intercropped plots, cotton-basil intercropping significantly reduced total pest infestation and led to a 50% reduced abundance of the pink bollworm. The intercropping also increased the abundance of spiders and crickets. Ghewande and Nandagopal (1997) reported that intercrops such as pearlmillet and soybean suppress thrips, jassids and leaf miners; castor suppresses jassids. They further mentioned that these plants act as traps or barriers for reducing pest incidence. According to Schulz and Janssens (2000), cotton-pigeon pea intercropping system allows the legume to benefit from the cotton pest management, whereas cotton could take advantage of synergetic effects from pigeon pea. According to Wenhua (2001), cotton-rape combination is a good example of intercropping for the reduction of insect damage in cotton.

From the studies that have been conducted worldwide, it has been established that there is great potential for integration of pest control measures on cotton. According to Ghewande and Nandagopal (1997), cost effective and highly efficient IPM package should include components such as resistant varieties, mass trapping of lepidopteran pests, use of biocontrol agents, moulting inhibitors, intercrops, natural products, soil solarization, allelopathy and judicious use of pesticides. Environmental conditions, cultivation practices, cost and social factors must also be considered for these components to be highly successful.

2.5 Leafhoppers (Jassids)

Leafhoppers are classified within one of the largest families of plant-feeding insects. They are hemipterans that belong to the family Cicadellidae. Leafhoppers feed by sucking the sap of vascular plants and are found in almost all the regions where such plants occur, from tropical rainforests to Arctic tundra. Several leafhopper species are important agricultural pests (Zahniser and Dietrich, 2008). Cotton leafhoppers, Jacobiella fascialis (Jacobi, 1912) are commonly known as jassids throughout the cotton industry. They

22 are small, leaf-feeding insects ranging in colour from green, through yellow- green to brown.

Many leafhoppers look alike and only their colours vary. They can be green, grey, tan, brown, and banded, which often leads to misidentification of the different species. According to Pyke and Brown (1996), at least two species are found in cotton in Australia, namely, the vegetable leafhopper, Austroasca viridigrisea and the cotton leafhopper, Amrasca terraereginae. The A. terraereginae species is the one that is similar to Jacobiella fascialis that occurs in South Africa. High and well-distributed rainfall and low temperatures encourage jassid reproduction (Wightman and Rao, 1993).

2.5.1 Life cycle The eggs are laid into the parenchymatous tissue of the underside of the leaflets. They are elongate or curved, whitish to greenish, and about 0.8 mm long. The eggs hatch in about 10 days. The nymphs resemble the adults but are very small and pale yellow-green. They undergo five nymphal instars before they reach adulthood in 3-4 weeks. Their cast skins usually remain on the lower surface of the leaf. The nymphs and adults are greenish yellow and wedge shaped but the nymphs do not have wings. The adults are small, elongate, wedge-shaped insects, about 3 mm long, with inconspicuous white spots on the head and pronotum. They hop fast, fly quickly, and can run in all directions when disturbed, hence the name “leafhopper” (Bissdorf, 2005). The nymphs and adults readily run backwards, sideways, or forwards at rapid paces. Their nymphal and adult stages last for 7-21 days and 35-50 days, respectively.

2.5.2 Crop damage and economic importance Heavy cotton leafhopper infestations impair the growth of cotton and cause a 40 to 100% reduction in the number of bolls and consequently the cotton yield (ARC, 1996). Severe infestation may cause plants to shed squares and small bolls although this rarely happens. Larger bolls may turn soft and spongy and fail to mature (Godfrey et al., 2008). Both the nymphs and the adult leafhoppers feed on the plant sap from tissues between the leaves. They suck

23 sap from young leaves mostly from the lower surfaces (Wightman and Rao, 1993). They suck out the liquid content, leaving behind the dead and empty cells, which have the appearance at first of whitening of the veins. The leaves then turn a pale red rust colour, drop downwards and dry up when the infestation is severe. Severe infestation results in a dry appearance of the crop known as “hopperburn”. This is caused by the toxic effects of the insects' saliva that vectors cotton viruses. The leaf tips become necrotic in a typical “V” shape (Wightman and Rao, 1993). Hopperburn reduces yield during the early stages of the crop. However, attack may not significantly reduce the yield towards the end of the season. Usually jassids are first noticed low in the canopy (Cotton Tales, 2007). Prolonged feeding or heavy infestations can result in damage to the middle and upper canopy to the extent where the upper leaf surfaces appear to be bleached almost white (Cotton Tales, 2007). Severe damage such as this may have an adverse effect on yield and, if insecticides are applied for jassids control, populations of beneficial insects may also be adversely affected.

2.5.3 Control and management of leafhoppers

2.5.3.1 Chemical control In fields where there has been low or selective insecticide use the jassid populations slowly build up through the season. Control of jassids should balance the risk of yield loss against the effects of insecticides on beneficial insect populations. Jassids are very susceptible to a range of insecticides, but preference should be given to more selective options. Broad-spectrum products, such as the organophosphates omethoate and dimethoate, are very effective, even at reduced rates – which may help to conserve beneficial insect populations. However, consideration must also be given to other pest species that are present. The use of low rates of these products against jassids causes resistance in aphids. If jassid infestations are higher near the edges of the field, treatment of just these areas is feasible (Cotton Tales, 2007). Godfrey et al. (2008) advise that before applying an insecticide, one must check for swollen, lumpy main veins on a sample of injured leaves to make sure that the field symptoms have actually been caused by leafhoppers.

Pyke and Brown (1996) observed that leafhoppers may build up to high numbers in fields that received few broad-spectrum insecticides, sometimes causing damage to the extent where the leaves appear white. They stated that it was important to weigh up leafhopper control against the risk of reducing beneficial insect populations.

Patil et al. (2007) conducted studies to evaluate the bio-efficacy of chlothianidin 50% WDG (Dantop), a new insecticide spray formulation at different dosages along with standard checks (imidacloprid and Acetamiprid) to combat cotton sucking pests under irrigated cotton in India. The results indicated that two sprays of Clothianidin 50% WDG rendered very good protection of crop against the early season sucking pests. After the first spray, the jassid population went down considerably registering 0.97 larva per leaf in plots sprayed with Clothianidin 50% WDG. Significantly high seed cotton yield was harvested from the Clothianidin 50% WDG treated plots. Rajendran (2000) reported that systemic insecticides such as methyl demeton @ 2.0 l/ha, dimethoate @ 2.0 l/ha and phosphamidon @ 1.0 l/ha could alleviate the problems due to jassids. The Institute for Industrial Crops recommended that a cost-effective, environmentally sound control program becomes possible when a seed treatment like Cruiser® is used to control jassids followed by one or two applications of Mospilan® as soon as leaf damage is noticed (Cotton SA Katoen, 2001).

® AVAUNT is a suspension concentrate stomach and contact insecticide that is also registered for the control of various insect pests in cotton including the jassids. Most beneficial insects and predatory mites are unaffected by ® ® applications of AVAUNT . This benefit is maximized when AVAUNT applications are commenced early in the growth season of the crop. Spinosad is also reported to perform well against jassids (Horowatz and Ishaaya, 2004).

2.5.3.2 Biological control Natural enemies usually keep leafhoppers from building up large populations in cotton. However, if large numbers migrate to cotton from other hosts, treatment may be needed if extensive symptoms appear. Any contact or systemic insecticide spray is adequate. A range of parasites attack jassid eggs and nymphs. Predators of adults probably include ladybirds, lacewing larvae, and spiders (especially lynx spiders). Rajendran (2000) reported that fungi like Metarhizium anisopleae have considerable promise against jassids.

Naturally occurring native predators such as coccinellids (Singh and Brar, 2004), chrysopids and syrphids, besides many parasitic wasps offer significant control of early season sucking pests such as jassids, aphids and thrips. An experiment was conducted by Krishi (2001) to study the efficacy of standardized formulation of botanicals on different crops against different pests in Ahmednagar District in India. Five percent neem oil along with the detergent solution was sprayed against the sucking pests on cotton in early stages of crop growth. This gave a very effective control of aphids, jassids and whiteflies. The combination of Trichoderma, neem oil, Chrysoperla, NPV, botanical extracts and vermicompost significantly reduced the reddening of cotton leaves and sucking pests’ infestation.

Between 2001 and 2002, Gandhi et al. (2006) conducted two field experiments to test the efficacy of neem oil (20 ml/kg) as a seed dressing and the effect was compared with systemic chemical insecticides imidacloprid (7 g/kg) and carbosulfan (7 g/kg) and Pseudomonas fluorescens (10 g/kg). The study revealed that the neem oil recorded minimum population of leafhopper and aphids and provided better yield compared to control. Although the systemic chemical insecticide imidacloprid gave better fruit yield, neem oil also recorded about twofold increase in fruit yield. Gandhi et al. concluded that neem oil could be used as a potential seed dressing for managing sucking pests.

2.5.3.3 Cultural control Hairy-leaved cotton has been found to resist leafhopper attack, but this trait is not used in Australian cotton cultivars because it makes the plant more susceptible to Heliothis and mites and also reduces quality.

Knight (1952) reported that it has been proved by research elsewhere that hairs of sufficient length and density, on the undersides of cotton leaves, confer immunity to jassid. Intercropping cotton with cowpea, groundnut, greengram, soybean and clusterbean in Andhra Pradesh was reported by Sabesh (2006-07) to be a good strategy to increase the effectiveness of natural enemies like coccinellids, syrphids, chrysopids, spiders, trichogrammids and Apanteles. Sabesh also reported that growing fodder jowar or maize as barrier crops around cotton and castor and marigold as trap crop was also found more advantageous to manage pests of cotton. Sabesh further mentioned that it is vital that cotton stubbles should be removed after last picking, without opting for ratoon crop or prolonging in the crop growth with irrigations and fertilizer applications. This is essential to break the cycles of problem pests in the system as a whole.

2.6 Locally available plants with pesticidal potential

2.6.1 Tobacco Nicotiana tabacum, or cultivated tobacco, is a perennial herbaceous plant. It has large, broad leaves that are pointed at the tip. The leaves are rich in nicotine and are used in cigarette making. The tobacco plant is a thick- stemmed annual bearing large leaves with short petioles or leaf stems. Leaf blades are often more than 50 cm long and half as wide. They rise in a spiral along the stem. Stems grow to heights between 1 and 2 metres and terminate in a cluster of flowers if not topped (Magness et al., 1971). Growth in the field from setting to harvest covers 3 to 5 months.

2.6.1.1 Biological activity of tobacco against insect pests Tobacco is one of those natural remedies that can be more poisonous than some chemicals and it can therefore damage the plant if used in higher

27 concentrations than recommended. Nicotine kills insects in general, including leafhoppers and it also kills viruses. Tobacco may be processed to obtain nicotine insecticides or used as mulching material (Sparks, 2002). Nicotine functions as an anti-herbivore chemical, being a potent neurotoxin with particular specificity to insects. Nicotine is therefore widely used as an insecticide, as it can easily penetrate the skin.

Sabesh (2006-07) reported that a study that was conducted in Andhra Pradesh on aphid management on cotton discovered that tobacco powder dusted on cotton helped in managing the aphid population. Tobacco leaf extract in water was used to protect crops from aphids and other soft bodied insects (Charles, 1929). Giles (1964) reported tobacco leaf powder to protect stored wheat from insect attack when admixed with the grains. Tobacco dried leaves were also used to protect stored paddy rice against Angoumois grain moth, Sitotroga cerealella when admixed with the grains (Satpathy, 1983). Its whole plant, leaf, branch and root aqueous extracts were reported to show insecticidal and repellent activities against jassids, the cowpea aphid, the green peach aphid and citrus leaf miner (Krishnamurthy, 1982, cited in Prakash and Rao, 1997).

Reddy and Rao (1990) isolated nicotine sulphate from tobacco and found it to protect the cotton crop from Aphis gossypii. Similarly, Prabhu et al. (1990) and Patil et al. (1990) reported nicotine sulphate isolated from waste tobacco leaves to show toxicity to Heliothis armigera, Spodoptera litura, Myzus persicae and Bemisia tabaci. Prakash and Rao (1997) mentioned that nicotine acts as a fumigant due to its volatility and also penetrates directly through insect integument. Nicotine preparations were reported to be toxic to lepidopterous pests of the turk crops (Swingle and Cooper, 1935). Cremlyn (1978) reported that nicotine also acted as non-persistent contact insecticide against the aphids, jassids, leaf miners, codling moth and thrips on a wide range of crops. However, its use rapidly declined due to its high mammalian toxicity (De Ong, 1971) and lack of effectiveness in cold weather (Prakash and Rao, 1997). According to Prakash and Rao (1997), other alkaloid components, which possessed insecticidal activity, were nornicotine,

28 neonicotine, nicotyrine and metanicotine. They further reported that nicotine, nornicotine and neonicotine were the potent insecticides but nicotyrine and metanicotine were comparatively less toxic to Aphis rumicis. Tobacco root and shoot aqueous extracts showed nematicidal activity to Rotylenchulus reniformis (Haseeb et al., 1988).

2.6.2 Thorn apple Thorn apple (Datura stramonium) belonging to family Solanaceae is a bushy, smooth annual weed that grows up to a metre high and has a distinct smell when crushed. The branching stem is spreading and cylindrical. Leaves are generally light dull green, ovate-triangular and acute with a margin incised into several lobes; they are borne on sturdy petioles (Chiej, 1984). Flowers are trumpet-like and can be white or purplish in colour. The average length of the flower is about 8 cm. Fruit is borne in capsules as large as walnuts, covered with short, soft thorns, hence the name "thorn apple" and its seeds are black (Lindley, 1985).

2.6.2.1 Biological activity of thorn apple against insect pests The whole plant is considered to be a narcotic. It contains tropane alkaloids that are sometimes used as a hallucinogen. The active ingredients are atropine, hyoscyamine and scopolamine, which are classified as deliriants. Because of the extremely high risk of overdosing, many deaths and hospitalisations are reported from recreational use, though this is not always the case. Water extracts from the thorn apple plant, branch, leaf, seed and flower were reported to possess insecticidal, anti-feedant and nematicidal properties against the pests of agricultural importance (Prakash and Rao, 1997). Its dried leaves admixed with stored grains were found to protect them from the infestation of insect pests (Giles, 1964). Its leaf extract in acetone was reported to show toxicity to fifth instar nymphs of Dysdercus cingulatus and third instar larvae of Spodoptera litura and Pericallia ricini (Rajendran and Gopalan, 1979). Its whole plant extract was shown to be toxic to the fruit borer, Earias vitella when tested on potted okra plants (Anonymous, 1986). Similarly, Kareem (1984) found its whole plant extract possessing insecticidal property against D. cingulatus. Balasubrahmanian et al. (1982) mentioned

29 that its leaf extract also possess insecticidal property against S. litura. In addition, its seed and leaf aqueous extracts were reported to kill the root-knot nematodes, Meloidogyne incognita and M. javanica (Mukherjee, 1983, cited in Prakash and Rao, 1997). Water and methanolic extracts of thorn apple leaf, bulb and stem incurred 75-100% mortality to the second stage larvae of Tylenchulus semipenetrans and Anguina tritici (Prakash and Rao, 1997). Oil extracted from thorn apple seeds also incurred 65-90% mortality to the larvae of the test nematodes (Kumari et al., 1986). The alkaloids, atropine, nicotine and scopolamine, isolated from its leaf, stem and bulb extracts shown toxicity to Tylenchulus semipenetrans and Anguina tritici (Uhlenbrock and Bijloo, 1959; Winoto, 1969; Kumari et al., 1986).

2.6.3 Khaki weed Khaki weed (Tagetes minuta), also known as Mexican marigold, is a herbaceous weed with a very strong smell. It produces small yellow flowers. Khaki weed can also be used as a soil improver (IZWA, 2010). The foliage has a musky/pungent scent, though some later varieties have been bred to be scentless. Tagetes minuta is an erect annual herb reaching 1 to 2 m (Soule, 1993). The leaves are slightly glossy green and are pinnately dissected into 4 to 6 pairs of pinnae. Leaf margins are finely serrate. The under surfaces of the leaves bear a number of small, punctate, multicellular glands, orange-like in colour, which exude a licorice-like aroma when ruptured. There are typically 3 to 5 yellow-orange ray florets, and 10 to 15 yellow-orange disk florets per capitulum. The heads are small, 10 to 15 mm long, and 10 to 20 mm in diameter, ray florets included. The heads are borne in a clustered panicle of 20 to 80 capitula (Meshkatalsadat et al., 2010). The dark brown achenes are 10 to 12 mm long, with a pappus of 1 to 4 tiny scales and 0 to 2 retrorsely serrulate awns, which are 1 to 3 mm long (McMahon, 2011).

2.6.3.1 Biological activity of khaki weed against insect pests There is evidence that the secondary compounds in Tagetes are effective deterrents of numerous organisms, including fungi (Chan et al., 1975), fungi pathogenic on humans (Camm et al., 1975), bacteria (Grover and Rao, 1978), roundworms in general (Loewe, 1974), trematodes (Graham et al., 1980),

30 nematodes (Grainge and Ahmed, 1988), and numerous insect pests through several different mechanisms (Saxena and Srivastava, 1973; Maradufu et al., 1978; Saxena and Koul, 1982; Jacobson, 1990). Many closely related plant secondary compounds have demonstrated medicinal value in humans (Korolkovas and Burckhalter, 1976; Kennewell, 1990). In vivo human studies of the secondary compounds of T. minuta have not been reported, although other Tagetes species have proven to be medically safe and efficacious (Caceres et al., 1987).

2.6.4 Garlic Garlic (Allium sativum) belongs to the onion family Alliaceae (Lee et al., 2009). It is a strong-smelling bulbous herb that serves as a repellent and prevents harmful insects from infesting the crops. It is an upright plant that grows up to about 60 cm tall. The long, sword-shaped leaves grow from the bulb beneath the surface of the soil (Vasista, 2010). It repels insects in general and some nematodes and fungi. Garlic further disorientates the insects that are already on the plant. This disorientation causes them to leave their hiding places and move around. Bronkhorst (2005) mentions that although the smell of the garlic will disappear about three hours after the crops have been sprayed, the repellent action will continue for a much longer time. Garlic contains a wealth of sulphur compounds; most important for the taste is allicin (diallyl disulphide oxide), which is produced enzymatically from alliin (S-2-propenyl-L-cysteine sulphoxide) if cells are damaged. Its biological function is to repel herbivorous animals (Katze, 2009). Garlic is believed to stem from Central Asia, although no wild form is known. Garlic, like other plants, has an exquisite defence system composed of as many different components as the human immune system. In order to protect itself from insects and fungi, garlic enzymatically produces allicin when it is injured. Thus, allicin is mother nature's insecticide. Allicin, an odorous and transient compound (Lin, 1990), was discovered by Cavallito et al. (1944) who first noted its potent antimicrobial activity. Allicin received a patent for its antifungal activity in test tubes. However, no clinical trials have been performed with allicin and it was never developed into a drug or commercial product due to its instability, inability to be absorbed, and offensive odour. Allicin itself is

31 considered to be of limited value inside the body and is presently regarded by the scientific community as just a transient compound, which rapidly decomposes to other compounds (Amagase et al., 2001).

2.6.4.1 Biological activity of garlic against insect pests Garlic has been traditionally considered an antiseptic, anthelmintic, anti- spasmodic, carminative, cholagogue, diaphoretic, digestive, diuretic, expectorant, febrifuge, and insect repellent (Simon et al., 1984). Garlic is sometimes grown as a pest-repelling plant by gardeners. Some companies have taken its pest-repelling properties a step further by isolating active compounds and marketing them in a spray-on formula. Garlic is often grown among flowers or root vegetables as a companion plant to protect other plants from being attacked by pests. In some small garden plots, rows of garlic are planted along the perimeter to act as a deterrent barrier. Garlic extracts have also been used as deterrents. In Europe, these extracts are freeze-dried and marketed as garlic pellets. The pellets are dissolved in water and then sprayed onto plants to protect them from being attached by greenfly or caterpillars. A disadvantage of these extracts is that the active sulphurous compounds have a pungent smell and this smell can mask the perfume of roses and other aromatic plants. Bissdorf (2005) reported that a combination of ginger, garlic and chilli plant extracts could be used as a control measure for cotton bollworm. Plant parts to be used must be disease free and stored away from direct sunlight and moisture.

Garlic clove extract was reported to be to be toxic to the pulse beetle, Callosobruchus chinensis (Quadri, 1973; Quadri and Rao, 1980). Garlic oil showed insecticidal activity against the khapra beetle, Trogoderma granarium (Bhatnagar-Thomas and Pal, 1974). In addition, garlic powder and extract protected wheat grains from infestation of the lesser grain borer, Rhyzopertha dominica when admixed with its powder and extract and did not adversely affect the viability of the grains (Zag and Bhardwaj, 1976). Chatterjee et al. (1980) reported garlic oil and its fractions to show toxicity to rice weevil, Sitophilus uryzae. When tested under laboratory conditions, Prakash et al. (1980) found garlic extract as an effective paddy grain protectant against

Angoumois grain moth, Sitotroga cerealella, and the lesser grain borer, R. dominica. Under natural conditions of insect infestation in farm warehouses, garlic extract also effectively minimized the losses in stored paddy caused by S. cerealella, R. dominica and S. uryzae (Prakash et al., 1982).

Bulb extract of garlic in acetone was found to show repellent and insecticidal activities against the cotton bug, Dysdercus cingulatus (Sundramurthy, 1979; Rajendran and Gopalan, 1979), cotton leaf armyworm, Spodoptera litura, and castor pest, Pericallia ricini (Rajendran and Gopalan, 1979). Garlic oil 2% protected the okra fruits from infestation of Earias vittela when sprayed on the crop (Sardana and Kumari, 1989).

Prasad et al. (1990) reported methanolic fractions of its bulb extract to be highly toxic to the tobacco caterpillar, Spodoptera litura, when tested individually against its third instar larvae by leaf disc method and also enhanced the activity of nuclear polyhedrosis virus when tested in combination. Chatterjee et al. (1980) isolated an active compound (1-3, diphenyl thiourea) as an insecticide against S. uryzae. The active component from garlic extract was isolated and identified as allitin, a mixture of diallyl di- and trisulphides (Amonkar and Banerji, 1971), which was found to inhibit cholinesterase activity in insects (Bhatnagar-Thomas and Pal, 1974) when admixed with the grains (Prakash et al., 1984). But its unpleasant odour and low persistence restricted its use as a general insecticide (Chadha, 1986).

CHAPTER 3: MATERIALS AND METHODS

3.1 Field experiment

Two trials were planted at the ARC-Institute for Industrial Crops at Kroondal, Rustenburg (25°39.0 S, 27°14.4 E, North-West Province, South Africa). As Rustenburg is one of the original cotton-growing areas in South Africa, the location was ideal for the study. The trial was planted on 16 and 17 October 2006 for the 2006/07 season. A follow-up trial was planted on 30 October 2007 for the 2007/08 season. The cotton cultivar, DeltaOPAL, was used.

3.2 Trial layout

During the 2006/07 season, 35 plots consisting of seven different treatments replicated five times were planted. Each plot consisted of ten rows each that were 10 m long. One-metre spacing was used between rows and a fifteen centimetres spacing between plants. Two metre spacing was used to separate the plots, while a three metres path was set between replications. The total trial size was 62 m x 76 m = 4 712 m2 (Figure 3.1). A randomised block design was used.

Rep Thorn Khaki Garlic Decis® Mospilan® Control Tobacco 1 apple weed Path (3 m) Rep Mospilan® Decis® Tobacco Control Khaki Thorn Garlic 2 weed apple 62m Path (3 m) Rep Thorn Decis® Garlic Tobacco Mospilan® Control Khaki 3 apple weed Path (3 m) Rep Control Thorn Khaki Tobacco Garlic Decis® Mospilan® 4 apple weed Path (3 m) Rep Decis® Mospilan® Thorn Khaki Tobacco Garlic Control 5 apple weed 76 m

Figure 3.1 Trial layout at Rustenburg for the 2006/07 season.

During the 2007/08 season, 28plots consisting of seven different treatments and replicated four times were planted. Each plot consisted of ten rows, each 10 m long. One-metre spacing was used between rows and a 15-cm spacing between plants. Two metre spacing was used to separate the plots, while a two metres path was set between replications. The total trial size was 46 m x 76 m = 3 496 m2 (Figure 3.2).

Rep Mospilan® Decis® Tobacco Control Khaki Thorn Garlic 1 weed apple Path (2 m) Rep Thorn Decis® Garlic Tobacco Mospilan® Control Khaki 2 apple weed 46m Path (2 m) Rep Control Thorn Khaki Tobacco® Garlic Decis® Mospilan 3 apple weed Path (2 m) Rep Decis® Mospilan® Thorn Khaki Tobacco Garlic Control 4 apple weed 76 m

Figure 3.2 Trial layout at Rustenburg for the 2007/08 season.

3.3 Land preparation, planting and weed control

Black cotton soil (approximately 55% clay) was cultivated by tractor to obtain a fine tilth, for planting. The trials were planted using a four-row planter (Figure 3.3) under irrigated conditions and 400 kg of 2:3:2 NPK fertilizer was applied at planting. Limestone ammonium nitrate (LAN) fertilizer was applied as a top dressing at a rate of 150 kg per ha at 3, 6 and 9 weeks after planting. A pre-emergence herbicide, Cotogard®, was applied at a rate of four litres per hectare at planting to control the weeds. After emergence, weeds were controlled by hand hoeing.

Figure 3.3 Planting using a four-row planter at Rustenburg.

3.4 Treatments

Four organic treatments, namely tobacco, khaki weed, thorn apple and garlic were applied. The organic treatments were compared with two synthetic chemical insecticide treatments, namely, Mospilan® and Decis®, and an untreated control. Each organic treatment was soaked in water overnight at room temperature. The treatments were prepared fortnightly 24 hours before the application was administered during the 2006/07 season. During the 2007/08 season, the treatments were prepared weekly 24 hours before spraying. During both field seasons, the same volume of each extract was prepared and the extracts were kept overnight in a laboratory at room temperature. The treatments were replicated five times during the 2006/07 season and four times during the 2007/08 season.

3.4.1 Preparation of plant extracts and synthetic chemical insecticides

3.4.1.1 Tobacco Four hundred grams of dry flue-cured tobacco (Nicotiana tabacum) leaves were crushed and soaked overnight in one litre of water. Afterwards, the extract was diluted in ten litres of water and applied fortnightly during the 2006/07 season. During the 2007/08 season the extract was diluted in ten litres of water and applied weekly.

3.4.1.2 Khaki weed Natural occurring khaki weed (Tagetes minuta) was used for the experiment. Four hundred grams of freshly-picked khaki weed leaves were soaked overnight in one litre of water. Afterwards, the extract was diluted in ten litres of water and applied fortnightly during the 2006/07 season. During the 2007/08 season the extract was diluted in ten litres of water and applied weekly.

3.4.1.3 Thorn apple Four hundred grams of fresh thorn apple (Datura stramonium) stems and leaves was soaked overnight in one litre of water. Natural occurring thorn apple was used for the experiment. Afterwards the extract was diluted in ten litres of water and applied fortnightly during the 2006/07 season. During the 2007/08 season the extract was diluted in ten litres of water and applied weekly.

3.4.1.4 Garlic During the 2006/07 season four hundred grams of freshly crushed garlic (Allium sativum) were soaked overnight in one litre of water. Afterwards the extract was diluted in ten litres of water and applied fortnightly. During the 2007/08 season the extract was diluted in ten litres of water and applied weekly.

3.4.1.5 Mospilan® Seventy-five grams of soluble Mospilan® powder (200 grams per kilogram acetamiprid) was applied at the equivalent of 200 litres of water per hectare. Mospilan, which is a registered insecticide on cotton leafhopper in South Africa, was applied in the field fortnightly during the 2006/07 season and weekly during the 2007/08 season. Mospilan® is a systemic, contact and stomach insecticide for the control of pests in citrus, cotton, tomatoes, canola, wheat, barley, oats, apples, pears and grapes (Plaaskem).

3.4.1.6 Decis® Two hundred and fifty millilitres of Decis® (a pyrethroid) (25 grams per litre Deltamethrin) was applied at the equivalent of two hundred litres of water per hectare. The mixture, which is a registered insecticide on cotton bollworms leafhopper in South Africa, was applied in the field fortnightly during the 2006/07 season. During the 2007/08 season the insecticide was applied weekly. Decis® is unique in having only one isomer of deltamethrin and this is the optimum isomer for insecticidal activity. For this reason deltamethrin can be used at lower rates than other pyrethroids and one can be assured that the entire active ingredient that is sprayed will be insecticidal. This is coupled with a long duration of activity, rapid knockdown and short pre-harvest intervals. Not only is Decis® effective against a wide range of insect pests (including bollworms and stainers), but it is also selective to many important beneficial insects such as lacewings (Bayer).

3.5 Spray application

The spray application was administered from twelve weeks after planting. Five applications were administered during the 2007/06 season and eight weekly spray applications were administered during the 2007/08 season. All treatments were applied as water-based sprays using a manual knapsack sprayer. Spray applications were administered in the morning when most pests were still sitting on the leaves and their natural enemies were not yet very active. Furthermore this practice was done to avoid application of the extracts during the heat of the day because the plant is then under extreme

38 stress, and the extracts must remain on the plant as long as possible, not evaporate rapidly (Guerena and Sullivan, 2003).

3.6 Insect scouting and damage rating

During the 2006/07 season 12 plants per plot were scouted fortnightly for American, red and spiny bollworm larvae twelve weeks after planting. During the 2007/08 season, from 12 weeks after planting onwards, twelve plants per plot were scouted weekly for the larvae of the bollworm complex (American, red and spiny bollworms). The experimental plots were scouted by walking diagonally through each plot in a zigzag pattern, while randomly choosing twelve plants from each plot. The number of pests found was recorded on the scouting form (Figure 3.5). From 12 weeks after planting, the damage caused to the leaves by leafhoppers per plant (Bambawale et al., 2004), taken from ten plants per plot, was determined fortnightly and weekly during the 2006/07 and 2007/08 seasons respectively.

Figure 3.4 illustrates the different physical leaf appearances that were used to rate the leafhopper damage on cotton. The leafhopper damage was indexed (Figure 3.6) as follows:

1 = 0-20% damage 2 = 21-40% (Leaf margins discoloured yellowish-green and curled) 3 = 41-60% (Leaf margins discoloured red and curled) 4 = 61-80% (More than the leaf margins discoloured red and curled) 5 = More than 80% of the leaf discoloured red and curled

3.7 Cotton seed yields at harvest

The cotton seed yields were determined at the end of the season. The two middle rows were harvested per plot from which the seed cotton yield per hectare was determined.

3.8 Statistical procedures

The total counts of each bollworm species and complex for the 12 plants were calculated and subjected to analysis of variance using the repeated measurements over time as a subplot factor. The Shapiro-Wilk test was performed on the standardised residuals to test for non-normality (Shapiro and Wilk, 1965) and to identify possible outliers. The Student’s t-test was calculated at the 5% level to compare treatment means. The data analysis was performed using SAS statistical software (SAS, 1999). The leafhopper appearances for each experimental plot were evaluated on a five point ordinal scale. The total frequencies R x C contingency table occurrences for Time x rating and Treatment x rating were subjected to a Chi-square analysis to compare pattern differences or associations. Furthermore the accumulation percentages over classes were used to calculate the median classes. A linear regression was fitted over time using the median class and responses. Data analysis for the seed cotton yield was performed using SAS statistical software (SAS, 1999). The data were subjected to Fisher's protected least significant difference (LSD) test to compare treatment means.

1 2

3 4

Figure 3.4 Different levels of leafhopper damage on cotton.

BOLLWORM COUNT Locality: Date: Treatment/Plot no: Insect Plant 1 Plant 2 Plant 3 Plant 4 Plant 5 Plant 6 American Red Spiny Complex Plant 7 Plant 8 Plant 9 Plant 10 Plant 11 Plant 12 American Red Spiny Complex

Figure 3.5 Scouting form for recording larvae of the bollworm complex.

TRIAL: Biological Insect trial: Rustenburg Locality: Date: Treatment/Plot no: Week Treatments 1 2 3 4 5 TOTAL Tobacco Khaki weed Thorn apple Garlic Mospilan Decis® Control 1 = 0-20%, 2 = 21-40%, 3 = 41-60%, 4 = 61-80%, 5 = More than 80%

Figure 3.6 Rating form for leafhopper damage.

CHAPTER 4: RESULTS AND DISCUSSION

4.1 AMERICAN BOLLWORMS

The results in Table 4.1 indicate that during the 2006/07 season, Decis® and tobacco treatments had a significant effect on the American bollworm larvae compared to the untreated control. The results are in line with a study conducted by Wan and Wan (1984) that Deltamethrin (Decis®) gave complete control of American bollworm. Examinations of Zahid and Hamed (2003) showed that 52% mortality of the 3rd instar larvae of the American bollworm was recorded 72 hours after a Decis® 10EC application. They further reported that the maximum mean mortality (percentage) was recorded with Lorsban 40EC (97.3%), followed by Larvin 80DF (52.0%), Decis® 10EC (24.0%), Fury- F 18.1EC (22.7%) and Fastac 5EC (20.0%), while no mortality was observed in the control treatment 24, 48 and 72 hours post application. Prabhu et al. (1990) and Patil et al. (1990) reported that nicotine sulphate extracted from waste tobacco leaves show control of American bollworm. The efficacy of tobacco leaves on the American bollworm larvae was also observed during this season. The number of American bollworm larvae in the plots that were treated with khaki weed, thorn apple, garlic and Mospilan®, did not differ significantly from the untreated control. The findings of this study disagree with the results of Horváth et al. (2004) that stated that Mospilan® 20 Sp provided adequate results in the field when sprayed to control Helicoverpa armigera. The efficacy of Decis® is supported by Martin et al. (2002), who showed that the control of H. armigera is usually achieved with insecticides, especially pyrethroids. However, some authors (Martin et al., 2002; Goldberger et al., 2005) reported that pests such as the American bollworm have developed resistance to most of the currently recommended insecticides, including pyrethroids. Iqbal et al. (1997) revealed that the lowest percent infestation (6.6%) of H. armigera was recorded by Larvin 80DF, followed by Decis®10EC (7.3%) compared to the control (26.2%) after only one application. Some studies that were conducted previously lead to diverse and conflicting results about pyrethroids. In West Africa, deltamethrin susceptibility in H. armigera was surveyed annually from 1984 (Martin et al.,

2002). Pyrethroid resistance was detected in 1996 (Alaux, 1997; Vassal et al., 1997). At the same time, pyrethroid resistance was also detected in South Africa (Ochou et al., 1998).

During the 2007/08 season, the maximum population reduction was once again observed in the plots treated with Decis®, which differed statistically from the population reduction of American bollworm larvae in plots treated with thorn apple, garlic, khaki weed, tobacco, Mospilan® and the control (Table 4.1). The uncontrolled plots exhibited the highest significant number of American bollworm larvae but did not differ significantly from the plots that were treated with thorn apple and garlic. Contrary to the findings by Bissdorf (2005) that garlic plant extract could be used as a control measure for cotton bollworm, the extract did not differ significantly from the untreated control. Showler et al. (2010) reported that garlic extract and oil have been used as insecticides against various insects on numerous crops, but there are contradictions in the findings with regards to insecticidal or repellent properties. Plots that were treated with khaki weed, tobacco and Mospilan® had a significantly lower number of larvae compared to the untreated control. No significant differences were observed among the treatments that were treated with thorn apple, garlic, khaki weed, tobacco and Mospilan®. In Nigeria botanical insecticides have been extracted from various plants including tobacco and garlic (Oruonye and Okrikata, 2010). Their biological properties have been tested and found to include significant insecticidal and repellent effects against insect pests.

A significantly higher number of American bollworm larvae were observed at 15 weeks after planting during the 2006/07 season (Table 4.5 & Figure 4.2). This is the peak of bollworm larvae occurrence during the vulnerable flowering stage of cotton (Van Hamburg and Guest, 1997). A reduction in population of American bollworm larvae occurred from 19 to 22 weeks after planting, when the average numbers of larvae did not differ significantly from one week to another. At 22 weeks no American bollworm larvae were recorded. At this stage the cotton bolls are bursting and there are fewer immature bolls for the larvae to feed on. While considering the economic injury levels of the different

44 bollworms (American bollworm and bollworm complex – 5 larvae per 24 plants; red and spiny bollworm – 2 larvae per 24 plants (ARC, 1996)), the economic threshold level of 5 bollworm larvae per 24 plants was not exceeded throughout the sampling period. A maximum decrease in the mean numbers of American bollworm larvae during the 2007/08 season was recorded at 20 weeks after planting which was significantly different and lower than that in other weeks (Table 4.6 & Figure 4.3). The significantly higher population at 13 weeks after planting corresponds with the findings by Roome (1975). This author reported that oviposition of the H. armigera population on sorghum and cotton was correlated with flower production, but the level of oviposition depended on the coincidence between flower production and the state of fertility of the bollworm population. Similar results have been found in Tanzania by Kabissa et al. (1996) who reported that the peak abundance of eggs and larvae of H. armigera occurred between the 8th and 13th weeks. Female oviposition on cotton was also found to be initiated by first flowering (bud formation) (Anonymous, 1975). Although a significant decrease in population numbers was observed from week 13 to week 14, the population was still significantly higher than at 15 to 22 weeks after planting. From 15 to 19 weeks, the levels of infestation by American bollworm larvae did not differ significantly from each other. The economic threshold level of 5 bollworm larvae per 24 plants was exceeded in all the weeks except at 20 and 21 weeks after planting.

Table 4.1 The mean overall number of American bollworm larvae after treatment with different extracts and insecticides on cotton at Rustenburg during the 2006/07 and 2007/08 seasons. Treatments Larvae per 12 plants a Larvae per 12 plants a 2006/07 2007/08 Tobacco 0.52 b 4.35 b Khaki weed 0.82 ab 4.70 b Thorn apple 0.70 ab 5.00 ab Garlic 0.76 ab 4.78 ab Mospilan® 0.72 ab 4.28 b Decis® 0.60 b 3.00 c Control 1.00 a 5.73 a

LSD (p = 0.05) 0.3504 1.0135 4.654 EMS (df = 24) 0.7205 a Values followed by the same letter do not differ significantly at the 5% test level according to Student's t-LSD test.

4.2 RED BOLLWORMS

The results in Table 4.2 demonstrate that the maximum mean efficacy during the 2006/07 season was recorded in plots that were treated with Decis® followed by tobacco, Mospilan®, khaki weed, garlic and thorn apple. The control plots had on average significantly higher numbers of red bollworm larvae. Although all the treatments were at par in their reduction of red bollworm larvae, the effect of the Decis® treatment was significantly different and more effective than the thorn apple and garlic treatments. The data presented in Table 4.2 indicate that the plots treated with Decis® had the lowest number of red bollworm larvae during the 2007/08 season. The plots that were treated with tobacco, thorn apple, khaki weed, garlic and Mospilan® were at par for reducing the red bollworm larvae, as there is no significant difference among their effectiveness. Several authors (Sundramurthy, 1979; Rajendran and Gopalan, 1979; Simon et al., 1984; Manjunath, 2004; Bronkhorst, 2005; Phillips, 2005) have reported that garlic’s mode of action is that of a systematic repellent, but this effect was not observed in this trial. Here too, the control plots exhibited significantly higher numbers of red bollworm larvae compared to all the other treatments.

During the 2006/07 season, the mean numbers of red bollworm larvae were significantly higher at 19 weeks after planting, compared to the other weeks (Table 4.5 and Figure 4.2). The high numbers of red bollworm larvae were observed when the cotton bolls were formed (at 19 weeks) rather than at square and flower formation. This concurs with the findings by Campion (1967) who reported that the red bollworm larva spends most of its larval cycle inside the cotton boll. During the 07/08 season, significantly higher numbers of red bollworm larvae were observed at 14 and 15 weeks after planting (Table 4.6 & Figure 4.3). At 17 weeks after planting, the lowest population number was observed, which was significantly lower than at 13 to 16 weeks after planting.

However, the number of larvae at 17 weeks after planting did not differ significantly from the numbers of larvae that were found at 18 to 22 weeks after planting. During the 2006/07 season, none of the treatments reached the economic threshold level of 2 larvae per 24 plants. In contrast, during the 2007/08 season, only the Decis® and Mospilan® treatments were below the economic threshold level.

Table 4.2 The mean overall number of red bollworm larvae after treatment with different plant extracts and insecticides on cotton at Rustenburg during the 2006/07 and 2007/08 seasons.

Treatments Larvae per 12 plants a Larvae per 12 plants a 2006/07 2007/08 Tobacco 0.44 bc 1.40 b Khaki weed 0.50 bc 1.25 b Thorn apple 0.58 b 1.38 b Garlic 0.54 b 1.23 b Mospilan® 0.46 bc 0.98 b Decis® 0.24 c 0.40 c Control 0.90 a 1.85 a

LSD (p = 0.05) 0.2933 0.4262

EMS (df = 24) 0.5048 0.8230 a Values followed by the same letter do not differ significantly at the 5% test level according to Student's t-LSD test.

4.3 SPINY BOLLWORMS

Table 4.3 shows that during the 2006/07 season, the average numbers of spiny bollworm larvae after treatment were comparatively lower than the control in all the treatments except for the plots that were treated with Mospilan. The plots treated with tobacco and Decis® exhibited the lowest numbers of spiny bollworm larvae than the other treatments. However the plots that were treated with Decis® did not differ significantly from the plots that were treated with garlic, thorn apple and khaki weed. The efficacy of Decis® corresponds with the study by Mambiri and Amadalo (1988) who observed that the insecticides that performed well in the reduction of the infestation of cotton by H. armigera and E. insulana were Decis®, Karate, and Baythroid. It has previously been reported that the whole plant extract of thorn apple (Anonymous, 1986) and 2% of garlic oil (Sardana and Kumari, 1989) protected okra from Earias vittela infestation. Figure 4.1 shows the feeding hole in the cotton boll. The holes can be with or without larvae, however they are usually blocked by excrement (Vennila et al., 2007). The highest population reduction of spiny bollworm larvae during the 2007/08 season was observed in the plots treated with Decis® (Table 4.3). However, the population reduction did not differ significantly from the plots that were treated with Mospilan® and khaki weed. The number of spiny bollworm larvae in the plots that were treated with thorn apple did not differ significantly from the untreated control. No significant differences were observed amongst the plots that were treated with garlic, tobacco, khaki weed and Mospilan®. Garlic has been previously reported to be active as a repellent, antifeedant, bactericide, fungicide and nematicide (Graigne et al., 1985; Mason and Linz, 1997) and in this trial garlic significantly reduced the number of the spiny bollworms compared to the control.

During the 2006/07 season, the number of spiny bollworm larvae was significantly lower at 13 and 22 weeks after planting compared to all the other weeks. The highest significant number of spiny bollworm larvae was recorded at 18 weeks after planting (Table 4.5 & Figure 4.2). This is in line with the findings of Klein et al. (1982) who reported that E. insulana is a serious pest of

49 cotton in late summer, when most of the plants have already started producing bolls. Weeks 14, 15, 16, 17, 19, 20, 21 (ranging from 0.46 to 0.63 larvae per 12 plants), did not differ significantly from each other but differed significantly from the low number of spiny bollworm larvae at 13 and 22 weeks and the high number at 18 weeks. The results in Table 4.6 indicate that higher numbers of spiny bollworm larvae during the 2007/08 season were observed at 19 weeks after planting and only differed significantly from the numbers at 13 weeks after planting. Vennila et al. (2007) reported that Earias population build up is large during the effective boll development phase of the crop causing damage to all fruiting forms. They further mentioned that seasonal fluctuations of larval populations depend upon the crop phenology in a given year. A reduction in population of spiny bollworm larvae was recorded at 13 weeks after planting but again the numbers were too low to be of any significance.

Table 4.3 The mean overall number of spiny bollworm larvae after treatment with different extracts and insecticides on cotton at Rustenburg during the 2006/07 and 2007/08 seasons. Treatments Larvae per 12 plants a Larvae per 12 plants a 2006/07 2007/08 Tobacco 0.20 d 0.75 b Khaki weed 0.48 bc 0.63 bc Thorn apple 0.48 bc 1.35 a Garlic 0.52 bc 0.90 b Mospilan® 0.64 ab 0.63 bc Decis® 0.38 cd 0.30 c Control 0.78 a 1.35 a

LSD (p = 0.05) 0.2425 0.4018

EMS (df = 24) 0.345 0.7314 a Values followed by the same letter do not differ significantly at the 5% test level according to Student's t-LSD test.

Figure 4.1 Damage and excrement on the cotton boll that was caused by a spiny bollworm larva.

4.4 BOLLWORM COMPLEX

Table 4.4 summarises the results that were obtained from the average of the total number of bollworm larvae, namely American, red and spiny bollworms during the 2006/07 season. The number of larvae observed in the control treatment was significantly higher than in the other treatments. The tobacco treatment showed significant repellent and insecticidal activity against the bollworm larvae. In a study conducted by Khan et al. (2000), it was revealed that a reduction of the bollworm complex of more than 92% was achieved when plants were treated with Deltaphos, which is a pre-mixed insecticide containing deltamethrin and triazophos. Charles (1929) revealed that a tobacco leaf extract in water has been used to protect crops from aphids and other soft bodied insects. During the 2007/08 season, all the tested treatments significantly reduced the mean number of the larvae population compared to the control (Table 4.4). The lowest number of bollworm complex larvae was recorded on the plots that were treated with Decis®. The number of larvae observed in the control treatment was significantly higher than the other treatments. Besides the two chemical treatments, plots that were treated with tobacco exhibited the lowest significant number of bollworm larvae compared to garlic, thorn apple and the control. Kumar et al. (2009) found that the combination of tobacco leaves and hookah water which contains nicotine protects the foliage from pest and pathogens. During the 2007/08 season, the numbers of bollworm larvae exceeded the economic threshold of 5 larvae on all the treatments.

The data presented in Table 4.5 and Figure 4.2 reveal that during the 2006/07 season, the number of bollworm larvae was significantly lower at 22 weeks after planting compared to all the other weeks, and at 15 weeks the number of bollworm larvae was significantly higher. The high American bollworm numbers at 15 weeks made the biggest contribution to the total number of bollworms. The data presented in Table 4.6 and Figure 4.3 show that at 13 weeks after planting the number of bollworm larvae was significantly higher during the 2007/08 season. Although the numbers of bollworm larvae differed significantly at 13, 14 and 15 weeks, these weeks had the highest significant numbers of bollworm larvae compared to 16 to 22 weeks after planting. The high number of American bollworm larvae at 13 weeks made the biggest contribution to the total number of bollworms. Obopile (2007) reported that the abundant food supply during the wet seasons favours the development of large populations of H. armigera. High rainfall (838 mm) was received in 2008 compared to 2007 (543 mm). At 20 weeks after planting the lowest number of bollworm larvae was observed. However the number did not differ significantly from the numbers that were found at 16, 18 and 21 weeks after planting.

Table 4.4 The mean overall of the total number of bollworm complex larvae after treatment with different extracts and insecticides on cotton at Rustenburg during the 2006/07 and 2007/08 seasons.

Treatments Larvae per 12 plants a Larvae per 12 plants a 2006/07 2007/08 Tobacco 1.16 d 6.50 cd Khaki weed 1.80 bc 6.58 cd Thorn apple 1.76 bc 7.73 b Garlic 1.82 b 6.90 bc Mospilan® 1.82 b 5.88 d Decis® 1.22 cd 3.70 e Control 2.68 a 8.93 a

LSD (p = 0.05) 0.5884 0.9519

EMS (df = 24) 2.0321 4.1056 a Values followed by the same letter do not differ significantly at the 5% test level according to Student's t-LSD test.

Table 4.5 Mean overall number of bollworm larvae per 12 plants at different time intervals after application of different insecticides during the 2006/07 season.

Number of larvae per 12 plants a Weeks American Red Spiny Complex 13 1.0c 0.51bcd 0.09c 1.60de 14 1.37b 0.6bc 0.54b 2.51b 15 1.94a 0.66b 0.46b 3.06a 16 0.97c 0.31cde 0.46b 1.74cde 17 0.89c 0.29de 0.51b 1.69de 18 0.69c 0.34cde 1.20a 2.23bc 19 0.29d 1.09a 0.63b 2.00bcd 20 0.11d 0.77b 0.51b 1.40e 21 0.06d 0.6bc 0.57b 1.23e 22 0.0d 0.06e 0.00c 0.06f

LSD (p = 0.05) 0.3482 0.2858 0.3017 0.5419

EMS (df = 24) 0.54698 0.3684 0.4106 1.3248 a Values followed by the same letter do not differ significantly at the 5% test level according to Student's t-LSD test.

Table 4.6 Mean overall number of bollworm larvae per 12 plants at different time intervals after application of different insecticides during 2007/08 season.

Number of larvae per 12 plants a Weeks American Red Spiny Complex 13 11.79a 1.71ab 0.50b 14.00a 14 6.64b 2.00a 0.79ab 9.43b 15 4.14c 2.04a 0.93ab 7.11c 16 3.25cde 1.21bc 0.86ab 5.32def 17 4.04c 0.68d 0.93ab 5.64d 18 3.75c 0.89cd 0.75ab 5.39def 19 3.61cd 0.89cd 1.00a 5.50de 20 2.11e 1.07cd 0.86ab 4.04f 21 2.46de 0.75cd 0.89ab 4.11ef 22 3.68cd 0.86cd 0.93ab 5.46de

LSD (p = 0.05) 1.2257 0.5108 0.4657 1.4036

EMS (df = 18) 5.4049 0.9388 0.7801 7.0878 a Values followed by the same letter do not differ significantly at the 5% test level according to Student's t-LSD test.

Figure 4.2 below is the graphic illustration of the different infestation levels by bollworm larvae at different weeks after application of various treatments during the 2006/07 season as tabulated in Table 4.5. The graph illustrates the trends of the bollworm larvae populations during the different developmental stages of the cotton crop. It has been observed that the American bollworm larvae were more abundant earlier in the season and eventually subsided when the first bolls began to burst. Later during the season the larvae of the red and spiny bollworm were more abundant but dropped towards the end of season. Red bollworm larvae showed co-existence with American bollworm larvae earlier in the season and later in the season co-existence was observed between the red and spiny bollworm larvae. The graph shows that the American bollworm larvae did not exceed the economic threshold level between 13 and 22 weeks after planting. The spiny and red bollworms exceeded the economic threshold level only at 18 and 19 weeks, respectively. The bollworm complex exceeded the economic threshold level at 14 and 15 weeks, respectively.

Figure 4.3 and Table 4.6 illustrate the trends of the bollworm larvae populations during the different developmental stages of the cotton crop during the 2007/08 season. Like in the previous season, the American bollworm larvae were observed to be more abundant earlier in the season and eventually decreased when the first bolls began to burst. However, the bollworm larvae population was higher during this season compared to the previous season. The red bollworm larvae population were also observed earlier and decreased later in the season. The larvae of the red and spiny bollworm were constantly lower throughout the season. Red bollworm larvae showed co-existence with spiny bollworm larvae throughout the season.

While considering the economic injury levels of the different bollworms, the graph shows that American bollworm larvae did not exceed the threshold level at 20 and 21 weeks after planting. The red bollworm larvae reached the economic threshold level at 13, 14, 15, 16 and 20 weeks after planting. The spiny bollworm larvae only reached the economic threshold level at 19 weeks after planting. The bollworm complex exceeded the economic threshold level throughout the sampling period (13 to 22 weeks).

BOLLWORM COUNTS OVER TIME: 06/07

3.5 3.0

2.5 2.0

1.5 1.0

Average number of larvae Average 0.5 0.0 13 14 15 16 17 18 19 20 21 22 Crop age (Weeks after emergence)

American Red Spiny Complex

Figure 4.2 Seasonal dynamics of different bollworm larvae per 12 plants at different time intervals after application of different insecticides during the 2006/07 season.

BOLLWORM COUNTS OVER TIME: 07/08

16.0 14.0 12.0 10.0 8.0 6.0 4.0

Average number of larvae Average 2.0 0.0 13 14 15 16 17 18 19 20 21 22

Crop age (Weeks after emergence)

American Red Spiny Complex

Figure 4.3 Seasonal dynamics of different bollworm larvae per 12 plants at different time intervals after application of different insecticides during the 2007/08 season.

4.5 ANALYSIS OF VARIANCE

Table 4.7 presents the analysis of variance for the total bollworm counts during the 2006/07 season. For all variables there was significant evidence against normality. This was caused by kurtosis and not skewness due to the presence of several zeros in the data; therefore the interpretation of the analyses was done (Glass et al., 1972). From the analysis of variance it is clear there was not enough evidence (p > 0.59) for treatment by week interactions. However, there was enough evidence amongst the week interactions and amongst the treatment interactions for all the bollworm larvae, with the exception of the American bollworm (p = 0.17). Table 4.8 presents the analysis of variance for the total bollworm counts during the 2007/08 season. From the analysis of variance, it is clear that, here too, there was not enough evidence (p > 0.62) for treatment by week interactions. However, there was enough evidence amongst the treatment interactions and amongst the week interactions for all the bollworm larvae, with the exception of the Spiny bollworm (p = 0.69).

Table 4.7 Analysis of variance for the total bollworm counts out of 12 plants at Rustenburg during the 2006/07 season.

American bollworm Red bollworm Spiny bollworm Bollworm complex

Source df MS p MS p MS p MS p

Blok 4 0.671 0.5039 1.961 0.0143 0.960 0.0496 3.247 0.2073 Treat 6 1.199 0.1732 1.976 0.0072 1.696 0.0021 12.552 0.0005 Error a 24 0.720 0.504 0.345 2.032 Week 9 14.007 <.0001 2.946 <.0001 3.652 <.0001 22.832 <.0001 Week*Treat 54 0.442 0.8237 0.298 0.8200 0.386 0.5955 1.203 0.6563 Error b 252 0.547 0.368 0.411 1.324

Total 349 0.617 1.961 0.960 3.247

Table 4.8 Analysis of variance for the total bollworm counts out of 12 plants at Rustenburg during the 2007/08 season.

American bollworm Red bollworm Spiny bollworm Bollworm complex

Source df MS p MS p MS p MS p

Blok 3 6.984 0.2482 5.0035 0.0048 2.2952 0.0510 0.666 0.9203 Treat 6 27.828 0.0014 7.9071 <.0001 6.1059 0.0002 104.716 <.0001 Error a 18 4.65 0.8230 0.7313 4.10 Week 9 222.32 <.0001 7.4638 <.0001 0.5571 0.6956 256.09 <.0001 Week*Treat 54 4.98 0.6276 0.8648 0.6299 0.3321 0.9998 6.19 0.7146 Error b 189 5.40 0.9387 0.7801 7.08

Total 279 6.984 5.0035 2.2952 0.666

4.6 LEAFHOPPER DAMAGE

The slope on Figure 4.4 indicates the rate change and R2 (98%) points out the accuracy of prediction during the 2006/07 season. It further shows that the regression on the median rating is highly significant, which implies that each fortnight that was rated for leafhopper damage, differed significantly from the previous one with an increase of 0.185. Although leafhoppers appear as soon as the cotton seedlings are available in the field (Sikka et al., 1966), this population was visible and constantly increasing after the flowering stage. In Figure 4.5 the results indicate a significant difference ( 2 = 75.83, p < 0.001) in patterns over rating classes during the 2006/07 season. Two types of patterns could be identified. The first one consisted of ratings from the plots that were treated with Decis®, Mospilan® and tobacco, for which more significant leafhopper control was achieved considering that highest percentages of lower leaf damage (0-40%) were recorded. Khattak et al. (2004) found that a jassid population reduction of 48% was noticed in the plots treated with Mospilan 20 SP. According to Aslam et al. (2004), Mospilan is one of the most effective insecticides for the control of jassids, thrips and whiteflies. Krishnamurthy (1982, cited in Prakash and Rao, 1997) reported that aqueous extracts from a whole tobacco plant showed insecticidal and repellent activities against the jassids, cowpea aphid, the green peach aphid and citrus leaf miner. This supports the results obtained in the present study. The second pattern consisted of ratings from the plots that were treated with khaki weed, thorn apple, garlic and the untreated control. These treatments exhibited the highest leaf damage percentages. The control treatment had the highest percentage (10%) of leaves that were discoloured and curled. Figure 4.6 demonstrates the leafhopper damage on the plot that was treated with Decis® compared to the untreated plot.

2006/07 5

Rate = -1.64 + 0.185 x Week R2 = 98% 4

2 Rating ( median ) median ( Rating 1

0 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 Time(weeks)

Figure 4.4 Fitted linear regression on the median leafhopper damage rating over time that indicates a change rate per week during the 2006/07 season.

TreatmentxRating Patterns 2006/07 50

20 Frequency(%) 15

5 Chi-Square with 24df = 75.83 P<0.001 0 1 2 3 4 5 Rating Class Control Decis Garlic Khakiweed Mospilan Thornapple Tobacco

Figure 4.5 The total frequencies R x C contingency table occurrences for Treatment X Rating indicating interaction patterns between treatments and rating classes on the leafhopper damage during the 2006/07 season.

Figure 4.6 Leafhopper damage on cotton treated with Decis (left) and the untreated control (right) at 15 weeks after planting.

The slope on Figure 4.7 indicates the rate change and the R2 (97%) points out the accuracy of prediction during the 2007/08 season. It further shows that the regression on the median rating is highly significant, which implies that each fortnight that was rated for leafhopper damage differed significantly from the previous one with an increase of 0.226. Pyke and Brown (1996) observed that leafhoppers may build up to high numbers in fields that receive few broad- spectrum insecticides, sometimes causing damage to the extent where the leaves appear white. The graph presented in Figure 4.8 reveals that there was a significant difference in patterns over rating classes ( 2 = 33.46, p < 0.001). More significant leafhopper control was observed from the plots that were treated with Decis®, Mospilan® and tobacco. Almost 45% of the plots that were treated with Decis® and Mospilan® were found to have less leaf damage (0-20%). Cost-effective, environmentally sound control of leafhoppers becomes possible when the application of Mospilan® is administered as soon as leaf damage is noticed (Cotton SA Katoen, 2001). Patil et al. (2007) conducted a study to evaluate the bio-efficacy of Chlothianidin at different dosages along with standard checks (imidacloprid and Acetamiprid) to combat cotton sucking pests under irrigated cotton. They reported that after the first spray, the jassid population went down considerably in plots sprayed with clothianidin which was statistically on par with Acetamiprid. Untreated plots had significantly more damaged cotton leaves compared to the plots that were treated. None of the plots that were treated with Decis® and Mospilan® had leaves that were discoloured and curled compared to the control which had 100% of the that were discoloured and curled. Figure 4.9 shows the leafhopper damage on the plot that was treated with Mospilan® compared to the untreated plot. Figure 4.10 shows the discoloured and curled leaf on a control plot.

2007/08 5

Rate = -2.41 + 0.226 x Week R2 = 97% 4

2 Rating ( median )

0 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 Time(weeks) Figure 4.7 Fitted linear regression on the median leafhopper damage rating over time that indicates a change rate per week during the 2007/08 season.

TreatmentxRating Patterns 2007/08 50

20 Frequency(%) 15

5 Chi-Square with 24df = 33.46 P<0.001 0 1 2 3 4 5 Rating Class Control Decis Garlic Khakiweed Mospilan Thornapple Tobacco

Figure 4.8 The total frequencies R x C contingency table occurrences for Treatment X Rating indicate significant interaction patterns between treatments and rating classes on the leafhopper damage during the 2007/08 season.

Figure 4.9 Leafhopper damage on cotton treated with Mospilan® (left) compared to the untreated control (right).

Figure 4.10 Leafhopper damage on a cotton leaf from the untreated control plot.

4.7 SEED COTTON YIELD

The results in Table 4.9 reveal that plots that were treated with Mospilan® and Decis® had significant higher cotton seed yields of more than 5 ton/ha when compared to the plots that were treated with tobacco, khaki weed, thorn apple, garlic and control. However, the tobacco treatment gave significant higher yields than the khaki weed, thorn apple and untreated control but did not differ significantly from the garlic treatment. Matthews (1996) mentioned that yields of seed cotton have been increased significantly since modern chemical techniques have been used. However, simplistic approaches to the use of insecticides have led to their over-use and selection of resistant pest populations with subsequent crop failures in certain areas. Despite the fact that the cotton was attacked by leafhoppers and the bollworm complex, seed cotton yields of above two tons per hectare were obtained. These levels of yield are common under small-scale cotton production systems (Gouse et al., 2002). The average cotton yield in South Africa during the 2006/07 season was 2.2 tons per hectare (Cotton SA Katoen, 2001), which was below the average yields that were obtained from all the treatments in the trial. The world annual yield production of seed cotton has also increased in a constant manner since the early 1960s (with an annual average of around 2.2%). Yields in seed cotton rose from 0.86 ton/ha in 1960/61 to 2.14 ton/ha in 2006/07 (ICAC, 2008). The mean cotton seed yields obtained during the 07/08 season are presented in Table 4.9. The highest seed cotton yields of 1.25 and 0.83 ton/ha was recorded from the plots that were treated with Decis® and Mospilan® respectively. The tobacco and garlic treatments gave lower yields but did not differ significantly from the Mospilan® treatment. Plots that were treated with tobacco, garlic, khaki weed and thorn apple did not differ significantly from the control. Showler (2010) reported that garlic extracts resulted in enhanced fruit production and apparently has plant growth regulator properties when applied on sweet bell peppers. His findings are not corroborated by the results that were obtained in this study. Patil et al. (2007) reported that significantly higher seed cotton yield was recorded from Clothianidin 50% WDG treated plots which was on par with Acetamiprid 20 SP.

Table 4.9 Seed cotton yield in plots treated with different extracts and insecticides at Rustenburg during the 2006/07 and 2007/08 seasons.

Treatments Seed yield (ton/ha) a Seed yield (ton/ha) a 2006/07 2007/08 Tobacco 3.75 b 0.62 bc Khaki weed 2.71 c 0.52 c Thorn apple 2.87 c 0.52 c Garlic 3.06 bc 0.55 bc Mospilan® 5.04 a 0.83 b Decis® 5.06 a 1.25 a Control 2.86 c 0.51 c

LSD (p = 0.05) 0.7681 0.2989

EMS (df = 24) 0.3462 0.0405 a Values followed by the same letter do not differ significantly at the 5% test level according to Student's t-LSD test.

The average cotton yield of both the dry land and irrigated cotton in South Africa during the 2007/08 season was 2.8 tons per hectare (CottonSA, 2001), which was largely above the average yields that were obtained from all the treatments in the trial. The cotton seed yields in the trial were low during the 2007/08 season compared to the previous season. The sudden drop in the seed cotton yield during the 2007/08 season could possibly be attributed to the sudden change in the environmental conditions, which consisted of cool and cloudy weather throughout the season. Boyd et al. (2004) reported that cotton requires a minimum temperature of 16 C to grow and sunlight is necessary for the plant’s photosynthesis. They further mentioned that weather and pests (diseases, insects and weeds) can disrupt normal plant development throughout the growing season. The cotton yield is also directly proportional to the amount of water consumed by the cotton (ARC, 1996). The higher bollworm infestation compared to the previous season could also have contributed to the low seed cotton yields during the season.

Worldwide, 15% of cotton yield loss is due to insect damage (Kooistra et al., 2006). Matthews (1999) reported that infestations of red and American bollworms, together with cotton stainers, continued to keep yields of seed cotton generally below 500 kg/ha. Ahmad (1999) found that the bollworm and sucking pest complex cause about 20-40% yield losses in Pakistan. Obopile (2007) reported that H. armigera is estimated to cause yield loss of 15 to 30% on sorghum in Botswana. Ahmad et al. (1989) reported that in field cages even 0.5 jassid/leaf caused significant yield losses when numbers were maintained at the target level for the period of 40 days. Van Hamburg and Kfir (1982) and Kfir and Van Hamburg (1983) showed in economic threshold trials that an increase in insecticide applications did not correlate with an increase in yield. Using lower treatment thresholds than recommended will not necessarily increase yields (Eveleigh and Larsen, 2002). However, lower thresholds usually increase the number of sprays, insect control costs can escalate, and insect resistance will be exacerbated.

CHAPTER 5: CONCLUSION AND RECOMMENDATIONS

5.1 Conclusion

Cotton is one of the most important cash crops in South Africa. It sustains more insects than any other crop grown commercially world-wide (Krathi and Russell, 2009). These insects are mainly controlled using a broad spectrum of chemicals (Fadare and Amusa, 2003) due to considerable assured results from these pesticides. This resulted in other methods of controlling the insect pests, such as natural substances, being ignored. From the literature, it has been shown that the bollworm complex (Stam and Al-Mosa, 1990; Manjunath, 2004; Godfrey et al, 2008) and leafhoppers (Bhat et al., 1986; Javed et al., 1992; Ahmad et al., 2005; Zahniser and Dietrich, 2008) are some of the most common pests on cotton. Cotton leafhoppers cause leaf discolouring, drying and shedding in cotton plants and delay the plant growth. Cotton that was severely attacked by leafhoppers can have about 20% (Javed et al., 1992) to 25% (Bhat et al., 1986) reduction in cotton yield. Among the different pests attacking cotton, bollworms amount for 25-30% yield loss (Ahuja et al., 2008).

The excessive use of chemical insecticides has produced several undesirable effects including development of resistance to insecticides, toxic residues on lint and seed, and dangers to the environment, beneficial organisms (Hamilton and Attia, 1976) and man (Betz et al., 2000; Rother, 2000; Wilkins et al., 2000; Yousefi, 1999). Insect pests are known for developing resistance to chemical pesticides (Fitt, 1989; Forrester et al., 1993; Singh and Dhaliwal, 1993; McCaffery, 1998; Chaturvedi, 2007), resulting in higher dosages being used (Manjunath, 2004).

The concept of Integrated Pest Management (IPM) is becoming more popular (Sundaramurthy and Gahukar, 1998) because it encourages the use of several components in the pest control system in a harmonious combination, which has a minimal impact on the environment.

Plant extracts have the advantage that they contain a mixture of compounds which may significantly reduce the chances of tolerance or resistance build-up by insect pests (Thacker, 2002).

Despite numerous studies (Maradufu et al., 1978; Saxena and Koul, 1982; Patil et al., 1990; Prabhu et al., 1990; Prakash and Rao, 1997; Bissdorf, 2005) conducted on biological control in cotton, empirical evidence on plant extract impacts on the control of bollworms and leafhoppers is limited. Therefore, this study was intended at using locally available plant extracts to test for their biopesticide potential to control the cotton pests. The research focused on evaluating various plant extracts that could be packaged into an IPM strategy to manage bollworms and leafhoppers in field cotton.

The results of this study suggested that tobacco extract can be used to effectively control cotton pests and can be a good alternative for chemical insecticides. The fact that it was able to reduce the pest infestations makes it more useful and essential for controlling cotton pests. Previous studies (Luttrell et al., 1994; Krathi et al., 2002; Krathi and Russell, 2009) have revealed that the long-term use of synthetic chemicals poses potential environmental risks by killing natural enemies and create pest resistance. However, natural compounds break down easily and they do not cause environmental contamination and unforeseen consequences in ecosystems. Furthermore, plant extracts are also said to be of low toxicity to insects such as bees, butterflies and natural predators of pests (Mordue and Blackwell, 1993).

On average, during the 2006/07 and 2007/08 seasons, the Decis® and tobacco treatments exhibited significantly less bollworm larvae than the other treatments. Tobacco gave satisfactory control against the American bollworm larvae, while khaki weed, garlic and thorn apple were the least effective against the larvae. All the treatments were significantly effective against the red bollworm larvae but Decis® and Mospilan® proved to be more effective compared to plots sprayed with tobacco, khaki weed, garlic and thorn apple. Tobacco was the most promising biological pesticide against the spiny

71 bollworm larvae. Although khaki weed, garlic and thorn apple were promising biological pesticides against the bollworm complex, tobacco was the most effective. Mospilan® seemed to be more effective on the control of leafhoppers followed by Decis® and tobacco. Regardless of the fact that the cotton was attacked by leafhoppers and the bollworm complex, seed cotton yields proximal to and above 2.5 ton/ha were obtained from all the treatments during the 2006/07 season. Among the plant extracts, tobacco and garlic gave higher seed cotton yields compared to the khaki weed and thorn apple during the 2006/07 and 2007/08 seasons.

High numbers of American bollworm larvae occurred at 13 to 15 weeks after planting. This is the cotton boll-setting period when more bolls are still young. Fewer American bollworm larvae occurred towards the end of the season when most of the cotton bolls have burst. Red and spiny bollworm larvae numbers differed during the two seasons. The number of red bollworm larvae was very low at 17 weeks after planting, which was the first boll burst period. The number of spiny bollworm larvae was high at 19 weeks after planting. The bollworm complex numbers were high at 14 and 15 weeks after planting and low at 20 and 21 weeks after planting. The leafhopper damage on the leaves constantly increased over time due to the increase in leafhopper population.

While technical efficacy of botanicals is an important element, there are other factors such as the logistics of production and preparation that need to be considered (Morse et al., 2002). It is important to bear in mind that the impact of the plant extracts may vary between years, due to effects of climate and pest pressure. High rainfall during the seasons also influenced the effectiveness of the treatments because at certain times the applications were washed away by the rain. A high weed infestation also created competition for nutrients in the soil, thus resulting in lower but acceptable cotton seed yields. Indeed, there may be additional benefits from plant extracts that this study has not addressed, such as the reduction in input costs as a result of cheaper pest control. Although it was found in this study that the plant extracts has some control on the bollworm complex and leafhoppers, it is obvious that the chemical treatments were more effective in controlling the pests. The practical

72 implication of these results is that plant extracts can be integrated into a farming system especially under small-scale cotton production. The advantage of using plant extracts is that they are readily available in a farmer’s field. This is important especially for the small-scale farmers who will be able to lower pest control costs, while at the same time improving yields and profit margin. Generally the study concludes that the plant extracts have a significant effect on the reduction of the bollworm complex and leafhoppers as shown in Chapter 4. The results obtained indicate a greater usefulness for plant extracts as a source of bioactive ingredients capable of protecting cotton from infestation by bollworms and leafhoppers.

5.2 Recommendations

Given the time period (two years) and number of localities (one locality) of this study, limited conclusions can be drawn about the impact of plant extracts. There are some unanswered questions that require urgent attention. For South Africa to develop a large market of organic cotton farming, it is recommended that further research on organic pesticides be one of the key elements to achieve that goal. The potential application of biological insecticide should be adopted in cotton pest control programme for South Africa. According to Kranthi and Russell (2009), almost all insecticides have inadvertent adverse effects on naturally occurring beneficial insects. Therefore, further studies are needed to determine the effects of the plant extracts on natural enemies. It would be worthwhile to isolate and determine the insecticidal effects of other chemical compounds in the plant extracts under laboratory conditions. It is crucial to provide resource-poor farmers with cost-effective pest-control measures using resources that are readily available. Although the research findings were promising, they were not implemented on farmers’ fields at the completion of the project. It is therefore recommended that a guideline for the control of cotton bollworms and leafhoppers be compiled in the future. The use of plant extracts also need to be revisited and tested on farmers’ fields to demonstrate the usefulness of this technology to the farmers. Since the bollworm larvae are sometimes found inside the cotton bolls and the leafhoppers are commonly found on the underside of the leaves, thorough applications of the biopesticides should be done on all parts of the plants.

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