ABSTRACT
Sweetpotato weevil (Cylas puncticollis (Boheman)) infestation results in losses of millions of dollars annually. To protect crops in modern agriculture, integrated pest management can be a good alternative to synthetic insecticides. A field study was conducted during 2018 and 2019 cropping seasons to evaluate the efficacy of some botanicals on two orange fleshed sweetpotato varieties; Umuspo/1(V1) and Umuspo/3(V2). Three experiments conducted were: (i) The use of some botanicals as aqueous extract (Tephrosia vogelii, Alchornea cordifolia and Ageratum conyzoides) (ii) Earthing-up at three levels (once, twice and thrice) and (iii) Mulching with leaves of 3 plant species; Tephrosia vogelii, Alchornea cordifolia and Ageratum conyzoides (each 50 g at five and ten weeks after planting). The experiment was laid out in Randomized Complete Block Design (RCBD) with three replicates. Plot size was 6 m2. Parameters evaluated were weevil population density, progeny development, percentage colonization, root yield (marketable and unmarketable), yield-loss, damaged roots and percentage control. Results obtained from the studies indicated significant (P≤0.05) difference with aqueous botanical extracts which exhibited higher insecticidal activity against the C. puncticollis as the concentration level of the botanical extracts increased from 50 mls to 100 mls, plant extracts treatments were favourable compared to Imidacloprid and recorded significantly (P≤0.05) higher yields when compared with the control plots in 2018 and 2019. Application of 100 mls of the 3 plant extracts were effective against C. puncticollis and recorded similar yield to Imidacloprid insecticide in the two cropping seasons. The cultural practice of Earthing-up thrice and twice significantly recorded the least number of insect population density, adult insect emergence in damaged roots and had better yield and marketable roots in 2018 and 2019 compared to control plots. Mulch materials significantly (P≤0.05) reduced number of sweetpotato weevil population density, percentage colonization, damaged root, yield loss and better percentage control due to its insecticidal repelling potential on mulched plots compared to control plots. Plots mulched with T.vogelii indicated more yield in 2018 (7.15 t/ha), lower population density of C. puncticollis, least insect progeny development in 2018 (17.06) and 2019 (6.21) while A.conyzoides recorded higher yield in 2019 (5.73 t/ha). Significantly (P≤0.05) high yield of orange flesh sweetpotato was established by decomposed leaf mulch and reduced attack by C. puncticollis in both years. Umuspo/3 variety, significantly (P≤0.05) indicated higher yield and more insect progeny development than Umuspo/1variety in 2018. Umuspo/1 orange fleshed sweetpotato significantly (P≤0.05) recorded higher percentage control over Umuspo/3 variety in both years. Generally, an increase in insect population density was observed from 6weeks to 12weeks after planting, where 2019 recorded lower C. puncticollis population density over 2018 in the three experiments. Results from these studies revealed the efficacy of 100 mls botanical extract application and cultural practices of earthing-up twice, earthing-up thrice and mulching with insecticidal leaves for effective management of C. puncticollis. The botanicals used are common, abundant, eco-friendly, less hazardous, easily propagated and recommended to farmers in order to enhance orange fleshed sweetpotato production in Nigeria.
TABLE OF CONTENTS
Title Page
i
Declaration
ii
Certification
iii
Dedication iv
Acknowledgements
v
Table of Contents
vi
List
of Tables
xii
List
of Figures
xiv
List
of Plates xv
Abstract
xvi
CHAPTER 1: INTRODUCTION
1.1
Objectives of the Study 5
CHAPTER 2: LITERATURE
REVIEW
2.1 Sweetpotato (Ipomoea batatas (L.) Lam.)
6
2.1.1 Origin, distribution and diversity 6
2.1.2 Sweetpotato production 7
2.1.3 Sweetpotato nutrient content 9
2.1.4 Environmental requirement of sweetpotato 9
2.1.5 Agronomy
of sweetpotato
11
2.1.6 Orange fleshed sweetpotato (OFSP) 12
2.1.7 Importance of sweetpotato 15
2.2 Sweetpotato Insect Pests 24
2.2.1 Sweetpotato Hornworm taxonomy 25
2.2.2 Sweetpotato Butterfly taxonomy 27
2.2.3 Armyworms taxonomy 28
2.2.4 Sweetpotato Tortoise
Beetles taxonomy 32
2.2.5 Sweetpotato Loopers (cabbage
looper) taxonomy 34
2.2.6 Sweetpotato Whitefly taxonomy 40
2.2.7 Sweetpotato
Thrips
taxonomy 44
2.2.8 Sweetpotato Aphids
taxonomy 46
2.2.9 Sweetpotato Cutworm taxonomy 48
2.2.10 Sweetpotato White Grubs
taxonomy 53
2.2.11 Whitefringe Beetles taxonomy 55
2.2.12 Sweetpotato Wireworms
taxonomy 57
2.2.13 Sweetpotato
Rootworms
taxonomy 59
2.2.14 Sweetpotato Flea
Beetle taxonomy 61
2.2.15 Sweetpotato
Weevils
taxonomy 64
2.3 Control
strategies against sweetpotato weevil infestation 67
2.4 Neonicotinoids - Imidacloprid 78
2.5 Botanical Insecticides 80
2.6 Botanical Insecticides Mode of Actions 82
2.6.1 Repellents
83
2.6.2
Protectants 84
2.6.3 Feeding deterrents or antifeedants 84
2.6.4 Entomotoxicity 85
2.6.5
Growth retardants and development
inhibitors
86
2.6.6 Oviposition suppressant 87
2.6.7 Sterility/reproduction inhibitors 87
2.6.8 Attractants
88
2.7 Taxonomy of Tephrosia vogelii 89
2.8 Taxonomy of Alchornea cordifolia 92
2.9 Taxonomy of Ageratum conyzoides 95
CHAPTER 3: MATERIALS AND METHODS
3.1 Experimental Site 98
3.2 Soil Sampling 98
3.3 Meteorological Data 98
3.4 Planting Materials 98
3.4.1 Sweetpotato vines 98
3.4.2 Botanicals 99
3.4.3 Extraction procedure 99
3.4.4 Aqueous plant extract 99
3.5 Neonicotinoid - Imidacloprid 99
3.6 Experimental Design and Field Layout 101
3.6.1 Experimental design 101
3.6.2 Plot size and field layout 101
3.7
Treatments 103
3.7.1 Experiment one 103
3.7.2 Experiment two 104
3.7.3 Experiment
three 105
3.8 Agronomic
Practice 107
3.8.1 Field preparation 107
3.8.2 Fertilizer application 107
3.8.3 Weeding 107
3.8.4 Harvesting 107
3.9 Sweetpotato Data Collection 107
3.9.1 Insect count 107
3.9.2 Insect Study 108
3.9.3 Number of adult C. puncticollis and percentage colonization 108
3.9.4 Number and weight of sweetpotato roots per
plot at harvest 108
3.9.5 Number of marketable and unmarketable roots
per plot. 108
3.9.6 Percentage of infested (damaged) roots at
harvest 109
3.9.7 Percentage control 109
3.9.8 Yield losses 109
3.9.9 Storage
root yield (t/ha) 109
3.10 Statistical
data analysis 109
3.11 Analysis
of the plant materials used for the study 110
3.11.1 Phytochemical Analysis of
the Plant Materials used for the Study 110
3.11.2 Gas Chromatography-Mass
Spectrometry Analysis of the Plant Residues 111
CHAPTER 4: RESULTS
AND DISCUSSION
4.1 Results
113
4.1.1 Soil and Weather Characteristics
113
4.1.2 Main effects of variety, protectant
concentrations and their interactions on
population density of sweetpotato weevil
during 2018 and 2019
cropping seasons
116
4.1.3 Main effects of variety, protectant concentrations and their
interactions
on progeny development of sweetpotato at
harvest during 2018 and 2019
cropping seasons 120
4.1.4 Main effects of variety, protectant concentrations and their
interactions
on Cylas puncticolis percentage
colonization on orange
fleshed sweetpotato
123
4.1.5 Main effects of variety, protectant concentrations and their
interactions on
number of marketable and unmarketable roots
of orange fleshed sweetpotato
at harvest during 2018 and 2019 cropping seasons 127
4.1.6 Main effects of variety, protectant
concentrations and their interactions on
percentage
of damaged root, yield loss and effective control of C. puncticollis on
orange fleshed sweetpotato
at harvest 131
4.1.7 Main effects of variety, protectant
concentrations and their interactions on
number of roots,
stands and yield of orange fleshed sweetpotato
at harvest 134
4.1.8 Main effects of variety, earthing-up and their interactions on Cylas
puncticolis
population density on orange fleshed
sweetpotato 137
4.1.9 Main effects of variety, earthing-up and their interactions on progeny
development of sweetpotato at harvest 139
4.1.10 Main
effects of variety, earthing-up and their interactions on Cylas
puncticollis percentage colonization on orange fleshed sweetpotato 141
4.1.11 Main
effects of variety, earthing-up and their interactions on number of marketable
and unmarketable roots of orange fleshed
sweetpotato at harvest
144
4.1.12 Main
effects of variety, earthing-up and their interactions on percentage of
damaged root, yield loss and effective
control of sweetpotato weevil on
orange
fleshed sweetpotato 146
4.1.13 Main
effects of variety, earthing-up and their interactions on number of roots,
stands and yield of orange fleshed
sweetpotato at harvest 148
4.1.14 Main effects of variety, mulching and
their interactions on Cylas puncticollis
population density of orange fleshed sweetpotato
150
4.1.15 Main effects of variety, mulching and their interactions on progeny
development of sweetpotato weevil at harvest
153
4.1.16
Main effects of variety, mulching
and their interactions on Cylas puncticollis
percentage colonization on orange
fleshed sweetpotato 155
4.1.17 Main effects of variety, mulching and their interactions on number of marketable
and unmarketable roots of orange fleshed
sweetpotato at harvest 157
4.1.18 Main effects of variety, mulching and their interactions on percentage of
damaged root, yield loss and effective control of sweetpotato at harvest 159
4.1.19 Main effects of variety, mulching and their interactions on number of roots,
stands and yield of sweetpotato at harvest 161
4.1.20 Phytochemical analysis of botanicals
used 164
4.1.21. GC-MS analysis of volatile compounds in botanicals used 166
4.1.21.1 GC-MS analysis of volatile compounds
detected in Tephrosia vogelii
leaf 166
4.1.21.2
GC-MS analysis of volatile
compounds detected in Alchornea
cordifolia leaf 171
4.1.21.3
GC-MS analysis of volatile
compounds detected in Ageratum conyzoides
leaf 175
4.1.22 Biological
activities of some isolated volatile constituents of the test
plant materials.
179
4.2 Discussion 181
4.2.1 Experiment 1
181 4.2.2 Experiment 2 185
4.2.3 Experiment 3 187
4.2.4 Orange fleshed sweetpotato variety
189
4.2.5 Phytochemical analysis of botanicals
190
4.2.6 The gas chromatograph mass spectrometry
(GS-MS) analysis of the
botanical leaves
192
CHAPTER 5: CONCLUSION
AND RECOMMENDATION
5.1 Conclusion 195
5.2 Recommendations
197
REFERENCES
199
APPENDIX 229
LIST OF TABLES
2.1 Botanicals
used in this study 89
4.1 Result
of physical and chemical properties of soils of the experimental
site in
2018 and 2019 114
4.2 Mean rainfall (mm) and temperature (oC) at Isieke
Umuahia, Abia State in 2018
and 2019 115
4.3 Main effects of variety, protectant
concentrations and their interactions on
population density of sweetpotato weevil
during
2018 and 2019 cropping seasons 119
4.4 Main effects of variety, protectant concentrations and their
interactions on
progeny development of
orange fleshed sweetpotato at harvest in
2018
and 2019 cropping seasons 122
4.5 Main effects of variety, protectant concentrations and their
interactions on
Cylas puncticolis percentage colonization on orange fleshed sweetpotato in
2018
and 2019 cropping seasons
125
4.6 Main effects of variety, protectant
concentrations and their interactions on
number
of marketable and unmarketable roots of
orange fleshed sweetpotato at
harvest in 2018 and 2019 cropping seasons 129
4.7 Main effects of variety, protectant concentrations and their
interactions on
percentage of damaged root, yield
loss and effective control of C.
puncticollis on
orange
fleshed sweetpotato in 2018 and 2019 cropping seasons 133
4.8 Main effects of variety, protectant concentrations and their
interactions on
number
of roots, stands and yield of
orange fleshed sweetpotato at harvest in
2018
and 2019 cropping seasons 136
4.9 Main effects of variety, earthing-up
and their interactions on
Cylas puncticolis
population density on orange
fleshed sweetpotato duing 2018 and 2019
cropping
seasons 138
4.10 Main effects of variety, earthing-up
and their interactions on
progeny
development of orange fleshed
sweetpotato root at harvest in 2018 and 2019
cropping
seasons 140
4.11 Main effects of variety, earthing-up and their interactions on Cylas puncticolis
percentage colonization on
orange fleshed sweetpotato during 2018 and 2019
cropping
seasons 143
4.12 Main effects of variety, earthing-up and their interactions on number of
marketable and unmarketable roots of orange
fleshed sweetpotato at harvest
in 2018
and 2019 cropping seasons
145
4.13 Main effects of variety, earthing-up and their interactions percentage of
damaged root, yield loss and effective control
of sweetpotato weevil on
orange
fleshed sweetpotato at harvest
in 2018 and 2019 cropping
seasons 147
4.14 Main effects of variety, earthing-up
and their interactions on
number of roots,
stands and yield of orange fleshed
sweetpotato
at harvest in
2018 and 2019 cropping
seasons
149
4.15 Main effects of variety, mulching and their interactions on Cylas puncticollis
population density of orange fleshed
sweetpotato during
2018
and 2019 cropping seasons 152
4.16 Main effects of variety, mulching and their interactions on progeny development
of sweetpotato weevil at harvest in
2018 and 2019 cropping seasons 154
4.17 Main effects of variety, mulching and their interactions on Cylas puncticolis
percentage colonization on
orange fleshed sweetpotato during 2018 and 2019
cropping
seasons
156
4.18 Main effects of variety, mulching and their interactions on number of
marketable and unmarketable roots of orange
fleshed sweetpotato at harvest
in 2018 and 2019 cropping seasons 158
4.19 Main effects of variety, mulching and their interactions on percentage of
damaged root, yield loss and effective
control of sweetpotato at harvest in
2018
and 2019 cropping seasons 160
4.20 Main effects of variety, mulching and their interactions on number of roots, stands
and yield
of
Sweetpotato weevil at harvest in 2018 and 2019 cropping seasons 163
4.21 Phytochemical Analysis of Botanicals used
in this study 165
4.22 GC-MS volatile compounds detected in Tephrosia vogelii leaf 169
4.23
GC-MS volatile compounds detected in Alchornea cordifolia leaf 174
4.24 GC-MS volatile compounds detected in Ageratum cornyzoides leaf 178
4.25 Biological
activities of the plant materials used in this study 180
LIST OF FIGURES
3.1 Field
layout 102
4.1 Chromatogram of volatile compounds of Tephrosia vogelii leaf 167
4.2
Structures of Some Volatile Components in Tephrosia vogelii leaf 168
4.3 Chromatogram of volatile compounds of Alchornea cordifolia leaf 172
4.4
Structures of Some Volatile Components
in Alchornea cordifolia leaf 173
4.5
GC-MS Chromatogram of Ageratum conyzoides 176
4.6
Structures of Some Volatile Components in Ageratum conyzoides
leaf 177
LIST OF PLATES
3.1 Tephrosia
vogelii
100
3.2
Alcornea cordifolia
100
3.3
Ageratum cornyzoides 100
3.4 Powder form of botanical leaves (A) T. vogelii (B) A.
cordifolia
(C) A. conyzoides
100
3.5 Experimental
site showing planting of sweetpotato vines.
106
3.6 Experimental
site showing growing sweetpotato plants of Umuspo/1
(palmate leaf shape) and
Umuspo/3 (heart lobe shape) at 3 months after planting. 106
4.1 Marketable
roots of Umuspo/3 Orange-fleshed sweetpotato 126
4.2 Marketable
Roots of Umuspo/1 Orange-fleshed sweetpotato 126
4.3 Damaged (infested) roots of Umuspo/1
Orange-fleshed sweetpotato 130
4.4 Damaged (infested) roots of Umuspo/3
Orange-fleshed sweetpotato
130
4.5 Progeny development on damaged (infested)
roots of Umuspo/3
Orange-fleshed
sweetpotato 130
CHAPTER 1
INTRODUCTION
Sweetpotato (Ipomoea batatas (L.)Lam.) is a crucial meal protection
crop in many of the developing countries (Korada et
al., 2010).
Sweetpotato is a staple and meal protection crop in Eastern and Southern Africa,
and is mainly grown by small holder female farmers (Bashaasha et al., 1995; Andrade et al., 2009). Sweetpotato (Ipomoea batatas) is the world’s 6th
maximum crucial meal crop fed on, after rice (Oryza sativa L.), wheat (Triticum aestivum L.), potato (Solanum tuberosum L.), maize (Zea mays L.), and cassava (Manihot esculenta Crantz).
It is one of the 5th maximum
crucial crops in forty growing nations except rice, wheat, maize, and cassava
(Elameen et al., 2008). Sweetpotato
is likewise the
maximum crucial root crop in Eastern
Africa grown after cassava and potato (FAO, 2015). In 2013, sweetpotato has a total
production of 103 million tonnes globally (FAO, 2015). In the world, it is essentially
produced in Asia (accounting for as much as 76.1%) followed by the African continent
(19.5%) in 2013 (FAO, 2015). In 2014, China, Nigeria, Uganda, Indonesia, and
the United Republic of Tanzania were the high 5 producers of sweetpotato (FAO,
2015). Nigeria’s harvest estimate was 3.5 million metric tons, approximately
3.3% of total global production in 2014. Nigeria is being ranked as the 4th biggest
producer within the world and the third in Africa with a record of 4,013,786
metric tons in 2017 representing 3.6 % global production for 2017 (FAOSTAT,
2017).
In many nations, sweetpotato is grown
for its vines as planting material; leaves are regularly eaten as a vegetable, while
shoots and roots are used as animal feed.
In Nigeria, it is grown
mainly for the
enlarged storage roots, which might
be generally eaten fresh, boiled, fried or roasted and the leaves may be eaten
as a vegetable or by livestock as forage (Loebenstein et al., 2009; Agrodok, 2013). In Uganda and western Kenya, the sale
of fresh sweetpotato roots, vines and processed foods in both local and urban
markets is becoming increasingly popular thus contributing to household cash
income (Abidin, 2004; Kaguongo et al., 2012).
Orange fleshed sweetpotato is one of
the wealthy supplier of beta-carotene, a precursor of bio-available vitamin A,
and has the ability of preventing Vitamin A deficiency among rural resource-limited
farmers in lots developing nations (Jalal et
al., 1998; Jaarsveld et al., 2005; Low et al., 2007; Mwanga et al., 2003; Burri, 2011).
The sweetpotato weevil was discovered
to be the primary pest within tropical areas in Africa. Despite the crop’s monetary
significance, widespread sweetpotato weevil infestation results in losses of
millions of dollars annually (Jackai et
al., 2006). Weevils are broadly dispersed in tropical areas of the world,
and their control is the challenging issue confronted by farmers in primary
sweetpotato producing nations. Cylas
brunneus and Cylas
puncticollis are African species and are limited to Africa. The
African Cylas species often occur
together in fields and cause huge yield losses as much as 100% (Smit, 1997b). Sweetpotato weevils generally cause
severe damage to all the components of sweetpotato plant in the course of their
life cycle, from egg to adult. Female weevils excavate cavities, create egg-laying
punctures within the roots during egg laying activity and thereafter cover it with
dark excrement resulting in damaged roots (Capinera, 2001). Infested
tuber produce bitter taste, becomes unsuitable for human intake and animal feed
(Worku et al., 2014).
Many African farmers increasingly
resort to regular use of commercial synthetic pesticides because of the
severity of different insect pests affecting crops (Abate
and Ampofo, 1996). Synthetic pesticides contaminate the environment, a
treat to non-target organisms and have high levels of pest and disease resistance
(Elberth
and Nauen, 2000).
Also, the use of synthetic insecticides is not a permanent solution as it can
be disastrous to human health due to poor handling, elimination of natural
enemies for the pest and expensive for most resource constrained poor farmers. To
enhance the development of sustainable agricultural practices and promote
ecosystem services, application of synthetic insecticides have been increasingly
criticised as unsustainable and difficult to incorporate into agro-ecological
intensification programmes (Pretty et al., 2011; Bommarco, 2013; Tittonell
and Giller, 2013). Modern agriculture seeks to apply natural plant-based
insecticides to protect crops, as feasible plant pest management method and an
attractive alternative to synthetic insecticides in an increasingly regulated
world (Ehisianya et al., 2013).
Botanicals are friendlier and pose little
threat to the environment, non-target organisms or to human health (Isman,
2006). Recently, plants-based
natural products have been considered as one of the most promising source of
biorational products with new modes of actions to manage phytophagous insects (Dayan
et al., 2009; Rattan,
2010). Some plant materials
consisting of terpenes, flavonoids, alkaloids, phenols, and different associated
compounds were taken into consideration to be used as insecticides, antifeedants
or repellents, (Adeyemi,
2010).
The improvement
of an effective pest management strategy for key insect pests of sweetpotato
according to climatic factors and pest severity is ongoing by International
Potato Centre (CIP) through its worldwide programme. Orange fleshed sweetpotato
as a global nutritious food security crop, its awareness has resulted in a
gradual steady increase in the area of orange fleshed sweetpotato crop under
cultivation in Nigeria (Ammirato and Yamada, 2010). But notwithstanding this
positive development, orange fleshed sweetpotato production in Nigeria remains
bedeviled with several demanding challenges, which includes: root damage by
sweetpotato weevils resulting in low yield. The average yield of the crop is
still within a very low range of estimated ≤ 3.0 t/ha compared with average
yield values of about ≥ 15t/ha obtainable from other sweetpotato producing
nations of the world like China (Onwueme and Sinha, 1991; Odebode, 2004).
Despite the importance of sweetpotato to economic subsistence, growth in output
in the last three decades was accounted for by increase in land area (Ojiako,
2008) than by increase in yield. This was identified by farmers as Cylas species of which Cylas puncticollis (Boh.) (Coleoptera:
Brentidae) and C. brunneus (Fab.) are
restricted to Africa, as primary biotic constraint to sweetpotato production
and utilization worldwide (Chalfant et al.,
1990; Lenne, 1991; Wolfe, 1991). Some researches have proven that the primary
production constraint in Nigeria, was due to sweetpotato weevil damage with losses
ranging from 1-100% (Ehisianya et al.,
2011). As part of this ongoing research on botanical
insecticides from indigenous plants, three plants with chemotaxonomic
precedents of insecticidal properties were collected and tested on two varieties
of orange fleshed sweetpotato.
The
aim of this present work is to identify natural and safer bio-rational
pesticides by screening aqueous extracts from leaves of some selected plant
species for insecticidal activities on Cylas puncticollis and
cultural practices, in
the management of Cylas puncticollis on orange fleshed sweetpotato.
1.1 OBJECTIVES OF THE STUDY
The specific objectives of this study were
to:
1.
evaluate the effects of some botanical aqueous extracts, earthing up and
mulching in the management of sweetpotato weevil in the field.
2.
determine the minimum effective rate of the extracts, for the control of Cylas puncticollis in the field.
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