ABSTRACT
The African sweetpotato weevil (Cylas puncticollis Boheman) is one of the most important insect pests of sweetpotato in Africa. It ranks the number one constraint to sweetpotato production in Nigeria. A field study was conducted at the National Root Crop Research Institute Umudike, Abia state during 2015 and 2016 cropping seasons to evaluate the effect of intercropping three varieties of sweetpotato (UMUSPO-1, UMUSPO-3 and BUTTERMILK), with hot pepper (Capsicum frutescens Linn) on the management of sweetpotato weevil (C. puncticollis).The experiment consisted of three different intercropping patterns (i) sweetpotato intercropped with pepper using earthing up at 0 level, 2 levels and 3 levels, (ii) sweetpotato intercropped with pepper using three different pepper population densities (1m x 1m, 1m x 0.5 m and 1m x 0.25m) and (iii) sweetpotato intercropped with pepper using different times of introducing pepper i.e planting same time with sweetpotato, 2 weeks and 4 WAP, 2 weeks and 4 weeks before planting sweetpotato. The experiment was laid out in a Randomized Complete Block Design (RCBD) with three replicates. The plot size was 18m2. Parameters evaluated were weevil population density, marketable and unmarketable weight of crop, crop yield, root damage, root weight, yield loss, percentage colonization and number of roots produced. Result from the studies indicated that lower insect pest populations were recorded in the intercrop plots (0.22,0.70, 0.80, 0.88, 0.99, 1.05, 1.22 ) than sole crop plots (1.64, 1.77, 1.95, 2.03, 2.09, 2.17, 2.31, ) in both cropping seasons. Results showed that intercropping with earthing up at 2 and 3 levels, using higher pepper population densities of 20,000 and 40,000 plants per hectare and introduction of pepper 2 and 4 weeks before planting sweetpotato were significant (P ≤ 0.05) in lowering the weevil population (0.22, 0.99, 0.70, 0.80, 0.88, 0.07, 1.05 ) and also gave lower unmarketable yields of sweetpotato roots (0.00, 0.02, 0.03, 0.09, 0.16, 0.,0.08, 0.11) lower colonization (5.50, 6.20, 7.70, 8.20, 15.40,16.20, 10.20,) and lower yield loss (1.00, 6.30, 0.70, 3.20, 3.60, 4.30, 7.80,) of sweetpotato roots than the sole crops (2.05, 0.77, 57.0, 41.8, 66.10, 25.4). Higher unmarketable roots, higher root damage, higher colonization and higher yield losses were recorded in the sole crop plots and also when intercropped with no earthing up, when pepper was planted using a lower population density of 10,000 plants per hectare (1m x1m) and when sweetpotato was planted 2 and 4 weeks before pepper. Generally, higher marketable yields were recorded in the intercrops than the sole crop plots. Result from the study also indicated that intercropping did not affect the yield of sweetpotato hence some of the intercrop plots recorded higher root number (61.00, 57.00, 84.00, 50.30, 40.30) and root weight (5.85, 3.22, 5.78, 9.71, 7.81, 4.05) similar to the sole crops. Results from the studies revealed the potential of sweepotato and pepper intercrop with earthing up at 2 and 3 levels, using higher pepper population densities (20,000 and 40,000 plants per hectare) and introducing pepper 2 and 4 weeks before sweetpotato in the management of sweepotato weevil. Hence, the recommendation to resource poor farmers for effective control of sweetpotato weevil especially during dry seasons when the insect pest infestations are more prevalent in addition to reducing the cost of production of sweetpotato and increase food production in Nigeria.
TABLE OF CONTENTS
Title Page i
Declaration ii
Dedication iii
Certification iv
Acknowledgements v
Table
of Contents vi
List
of Tables xi
List of figures xii
List of Plates xiii
Abstract xiv
CHAPTER 1: INTRODUCTION
1.1 Introduction 1
1.2 Objectives
of the Study 7
CHAPTER 2: LITERATURE REVIEW
2.1 Origin
and Distribution of Sweetpotato 8
2.2 Botany
of Sweetpotato 8
2.3 Sweetpotato
Production 9
2.4 Importance of Sweetpotato 10
2.4.1 Food and nutritional values of sweetpotato 10
2.42. Economic value of sweetpotato 11
2.4.3 Industrial value 11
2.4.4 Medicinal value 13
2.5 Climatic Requirements and Propagation of
Sweetpotato 15
2.5.1 Climatic requirements 15
2.5.2 Propagation 15
2.6 Cultivation and Harvesting of Sweetpotato 16
2.6.1 Agronomic practices 16
2.6.2 Harvesting 18
2.7 Insect Pests of Sweetpotato 19
2.7.1 Sweetpotato weevil 20
2.7.2 Foliage feeders 33
2.8 Control of Insect Pests of Sweetpotato 38
2.8.1 Origin and distribution of pepper 41
2.9 Importance of Pepper 42
2.9.1 Medicinal benefits of pepper 42
2.9.2 Food and nutritional value of pepper 43
2.9.3 Economic importance of pepper 44
2.10 Ecological Requirements and Cultivation of
Pepper 45
2.10.1 Climatic requirements 45
2.10.2 Cultivation of pepper 46
2.10.3 Harvesting and storage of pepper 46
2.11 Insect Pests of Pepper 47
2.12 Intercropping 48
2.13 Intercropping and Insect Pest Population 49
2.13.1 Effect of time of introduction of component
crop on insect pest population 49
2.13.2 Effect of sweetpotato intercrop on insect pest
population 49
2.13.3 Effect of pepper intercrop on insect pest
population 50
2.13.4 Effect of earthing up on insect pest
population 50
2.13.5 Effect of spacing on insect pest management 51
2.14 Land Equivalent Ratio 51
CHAPTER 3: MATERIALS AND METHODS
3.1 Experimental Site 52
3.2 Sources of Planting Materials 52
3.3 Field Preparation 52
3.4 Experimental Design and Field Layout 53
3.4.1 Experimental design 53
3.4.2 Plot size and field layout 53
3.5 Treatments 55
3.6 Planting Operations 58
3.7 Agronomic Practices 58
3.8 Data Collection on Sweetpotato 59
3.8.1 Insect population count 59
3.8.2 Number of adult Cylas puncticollis and percentage colonization 59
3.8.3 Number and weight of sweetpotato of roots
per plot at harvest 60
3.8.4 Storage root yield 60
3.8.5 Percentage of damaged roots at harvest 60
3.8.6 Number of marketable and unmarketable roots 60
3.8.7 Yield loss 61
3.8.8 Land equivalent ratio 61
3.9 Data Collection on Pepper 62
3.10 Data Analysis 62
CHAPTER 4: RESULTS AND
DISCUSSION
4.1 Results 63
4.1.1 Effect of intercropping and earthing up on
population density of sweetpotato
Weevil
in 2015 and 2016 cropping seasons 63
4.1.2 Effect of intercropping on number of roots
and root weight of sweetpotato
at
harvest 67
4.1.3 Effect of intercropping on number of
marketable and unmarketable sweetpotato
Roots as infected by sweetpotato
weevil 71
4.1.4 Effect of sweetpotato weevil on sweetpotato
root damage, colonization and
Yield loss 74
4.1.5 Land equivalent ratio of sweetpotato and
pepper intercrop 77
4.1.6 Effect of pepper population densities on
population of Cylas puncticollis in
sweetpotato intercrop 78
4.1.7 Effect of pepper population density on number
of roots and root weight of
sweet
potato 81
4.1.8 Effect of pepper population density on
number of marketable and unmarketable
sweetpotato roots 83
4.1.9 Effect of pepper population density of
sweetpotato weevil on root damage
Colonization and yield loss of
sweetpotato 85
4.1.10 Effect of pepper population density on land
equivalent ratio in sweetpotato
intercrop 87
4.1.11 Effect of time of introduction of pepper in
sweetpotato intercrop on population
of
sweetpotato weevil 89
4.1.12 Effect of time of introduction of pepper on
number of roots and root weight of sweetpotato 91
4.1.13 Effect of time of introduction of pepper on
marketable and unmarketable
root
weight of sweetpotato 91
4.1.14 Effect of time of introduction of pepper on
sweetpotato root damage, colonization
and
yield loss by sweetpotato weevil 94
4.1.15 Effect of time of introduction of pepper on
land equivalent ratio (LER) in
sweetpotato
intercrop 102
4.3 Discussion 104
CHAPTER
5: CONCLUSION AND RECOMMENDATION
5.1 Conclusion 113
5.2 Recommendations
115
REFERENCES 116
LIST OF TABLES
4.1: Effect
of intercropping and earthing up on number of roots and root
weight
of sweetpotato in 2015 and 2016 cropping season 68
4.2: Effect
of intercropping and earthing on marketable and unmarketable
weight
of sweetpotato in 2015 and 2016 cropping
season 72
4.3: Effect
of intercropping and earthing on percentage root damage,
percentage
colonization and percentage yield loss of sweetpotato in
2015
and 2016 cropping season 76
4.4: Effect
of intercropping and earthing up on yield and total Land
Equivalent Ration(LER) in 2015 and 2016
cropping season 79
4.5: Effect
of pepper population densities on Cylas puncticollis
in
2015 and 2016 cropping season 80
4.6: Effect
of pepper population densities on number of roots and root
weight
of sweetpotato in 2015 and 2016 cropping seasons correct 82
4.7: Effect
of pepper population densities on marketable and unmarketable
weight of sweetpotato tubers in 2015 and
2016 cropping season 84
4.8: Effect of pepper population densities on
percentage yield loss and
percentage root damage of sweetpotato in
2015 and 2016
cropping seasons
86
4.9: Effect
of pepper population densities on Yield and Land
Equivalent Ratio (LER) in 2015 and 2016
cropping season. 88
4.10: Effect
of time of introduction of pepper on Cylas
puncticollis
Population in 2015 and 2016 cropping
seasons 90
4.11: Effect
of time of introduction of pepper on root number and
root
weight of sweetpotato in 2015 and 2016 cropping seasons 92
4.12 Effect
of time of introduction of pepper on marketable and unmarketable
root of sweetpotato in 2015 and 2016 cropping
seasons 93
4.15: Effect
of time of introduction of component crop on land
equivalent
ratio in 2015 and 2016 cropping seasons 103
LIST OF FIGURES
1: Field Layout 54
2: Effect of intercropping and earthing up
on population density of sweetpotato
weevil
in 2015 65
3: Effect of intercropping and earthing up
on population density of sweetpotato
weevil
in 2016 66
4: Effect of time of introduction of
component crop on percentage root
damage
of sweetpotato in 2015 cropping season 95
5: Effect
of introduction of component crop on percentage root damage of
sweetpotato
in 2016 96
6: Effect
of time of introduction of component crop (pepper) on
percentage
colonization of sweetpotato roots in 2015 cropping season 98
7: Effect
of time of introduction of component crop (pepper) on
percentage
colonization of sweetpotato roots in 2016 cropping season 99
8: Effect
of time of introduction of component crop (pepper) on yield
loss
of sweetpotato roots in 2015 cropping season 100
9: Effect of time of introduction of
component crop (pepper) on yield
loss
of sweetpotato roots in 2016 101
LIST
OF PLATES
1: Experimental site 64
2: Umuspo-1 (a), Buttermilk
(b) and Umuspo-3 (c) with pepper intercrops 69
3: Pepper sole crop (a) and
sweetpotato sole crop infested by weevil (b) 70
4: Sweetpotato roots-
Buttermilk (a), Umuspo-3 (b) and Umuspo-1 (c) 73
5: Sweetpotato roots damaged by sweetpotato weevil 75
CHAPTER
1
1.1
INTRODUCTION
Sweetpotato
(Ipomoea batatas [L.] (Lamack) is a dicotyledonous plant that
belongs to the family Convolvulaceae.
It is among the world’s most widely grown crops (Stevenson et al., 2009). It is a low labour, low cost and low risk crop
(Ehisianya et al., 2013) with
potential for yield improvement and year-round availability (Eddison et al., 2009). It is a crop of great
value widely grown in Sub-Sahara African, where it has helped in the
eradication of poverty and increased food security due to its high productivity
per unit area and time (National Root Crop Research Institute, 2005). The crop
is perennial with a creeping growth habit and it is normally cultivated through
vine cuttings worldwide. It supplies 3.9% of the caloric and 1.5% protein
intake for human requirement (FAO, 2004).
Globally,
sweetpotato ranks seventh among the most important food crops after wheat,
maize, rice, potato, barley and cassava (Tarakegn et al., 2014). In most countries including Nigeria, the cultivation
of sweetpotato is not locally intensed (Huaccho and Hijman, 2000). The area of
sweetpotato cultivation in Nigeria was estimated at 69,000 hectares in 1994 which
increased to 500,000 hectares by 2003 (FAO, 2004).
Sweetpotato
has several advantages within the context of African cropping system. It
produces food in a very short time, gives reliable yields in sub-optimal growth
conditions, and requires lower labour input than other staples. It serves as a
source of food in countries with the challenge of constant increase in the
prices of cereals and vitamin A deficiency especially the Orange-Fleshed
Sweetpotatoes (OFSPs) which are rich in beta-carotene, a substance that can
combat vitamin A deficiency (Low et al.,
2007).
The
importance of sweetpotato is increasing in Nigeria’s farming and food system
because it is easy to plant and mature early with enormous industrial and
economic potential (Chukwu,1997). It is grown in most parts of Nigeria as a
secondary crop but reaches intense level in some areas (Akoroda and Nwokocha,
1996). In Sub-Saharan Africa, it is being used to address vitamin A deficiency
which is a serious health and nutritional problem as it could cause the immune
system to be weak (Tewe et al., 2007).
Sweet
potato is most often consumed when peeled before or after boiling. In some cases the roots are prepared in form
of porridge. After peeling, sundried and milled, sweetpotato flour can be used
for sweetening local dishes and to prepare a fermented drink called “kunu” in the Northern and Central zones
zones of Nigeria. The dough made from sweetpotato is used to prepare a paste
locally known as “amala”. It can also be made into chips (Tewe et al., 2007). The crop has come to be
appreciated as a high fibre food and as green vegetables because of high level
of vitamin A, vitamin C, iron and potassium (Loebenstein and George, 2009).
Sweetpotato
weevil (Cylas puncticollis.) is the
most destructive insect pest of sweetpotato in Nigeria causing serious
hindrance to sweetpotato production. C.
puncticollis limits sweetpotato production by damaging vines, tubers and
occasionally the foliage, thereby reducing both the yield and quality of the
crop. In East Africa, C. puncticollis
causes 60-70% yield loss (Kabir et al.,
2001). Young sweet potato plants which develop from infested cuttings may be so
badly damaged that they may wilt and die. It is one of the most important
biotic factors limiting sweetpotato production in Africa (Kabir et al., 2001).
Some
cultural practices such as intercropping, prompt harvesting and earthing-up have
been evaluated and proven to be effective in the control of C. puncticollis (Emana, 1990). However
each component of these cultural practices only reduced the effect of C. puncticollis and its population to a
certain level. It is assumed that if some of these cultural practices are put
together as integrated pest management an effective management of C. puncticollis could be achieved.
Intercropping
is the growing of two or more species on the same field at the same time during
a growing season so as to produce a greater yield by making use of resources
that otherwise would not be utilized by a single crop (Elena, 2013). It often
reduces insect pest population compared with monoculture (Bukosvinszky et al., 2010). It is a common
agricultural practice among small scale farmers in West Africa and also one of
the most widespread traditional agricultural practices among small scale
farmers where it provides food and income at different periods of the year for
the family (Emede and Adegoke, 2011).
Intercropping
has also been associated with other advantages such as efficient use of
environmental factors, higher yield stability, soil protection, variability of
food supply increased return per unit area, reduction in pest attack and
insurance against crop failure (Beets, 1982). It plays a very good role in
small scale agriculture in developing countries and has been practiced
traditionally by small scale farmers in the tropics mainly for increased yield
and to avoid total crop failure (Tsubo and Walker, 2002).
As
the world population is increasing rapidly and must have to fulfill their food
requirement, an efficient technique for increasing productivity and use of
labour per unit area of available land is to intensify land use. Intercropping
serves as the most useful approach for this purpose. Previous researches indicated that pests are
less damaging in fields with a mixture of crops than in fields with a single
crop (Kat, 2016).
Research
shows that insects with a small host range, for instance those that attack only
cruciferous crops, are more easily reduced in number when host crops are
planted with non-host crops (Andow, 1991; Hooks and Johnson, 2003). The
diamondback moth, (Plutella xylostella), which only attacks cruciferous
crops, is an example of insect pest with a narrow host range. When a herbivore
meets a plant that it cannot feed on, it uses additional time and energy to
search for an acceptable plant. This shortens the time and energy the insect
has to cause crop damage or deposit offspring, and in some it causes the insect
to move away from the area. To find host plants, insects rely on visual,
olfactory, and tactile clues (Hugh and Oscar, 2012). When a non host plant is
present, it interferes with the ability of an insect to detect host plants by masking
the presence of the host plant physically or by producing volatiles that
confuse the insect. In this case, the “apparency” of host plants to insect pests
is reduced by diverse habitat (Hugh and Oscar, 2012).
Intercropping
has been associated with yield advantages due to better utilization of growth
resources and variable return per unit area of land (Muoneke and Mbah, 2007).
Generally, the practice of intercropping increases crop diversity which
provides both barriers to pest dispersal and more dwelling place for natural
enemies thereby reducing both colonization of the crop by pests and their
subsequent control (Risch et al.,
1987). Emeasor and Ezueh (1997) observed
that intercropping pepper intra row with cowpea (Vigna unguiculata) reduced flower thrips (Megalurothrips sjotedti) together with cowpea aphids (Aphis craccivora) on cowpea and cause an
improvement on cowpea yield compared
with sole cropped cowpea. Asawalam et al.,
(2012) observed that intercropping cowpea with turmeric reduced some major insect
pests of cowpea in the test area. .
Pepper
(Capsicum spp) are moderately deep
rooted crops that belongs to the family Solanaceae (Grubben et al., 2004.). It is an erect herb or sub shrub up to 2.5m tall, much branched,
grown as annual but in home gardens sometimes a short term perennial. Pepper is an important agricultural crop not only
because of its economic importance but also due to the nutritional and medicinal
value of its fruits as well as being excellent source of natural colours and
antioxidant compounds (Howard et al.,
2000). It is the world’s second important vegetable, ranking after tomatoes and
it is the most produced type of spice for flavouring and colouring of food
while providing essential vitamins and minerals.
Pepper
is cultivated through seed which usually germinates 6-21 days after sowing
(Grubben et al., 2004). They are
consumed in fresh, dried or processed form. In salads, the non pungent fruits usually called
sweet peppers are consumed in fresh forms, but more commonly cooked, fried or
processed together with other foods. The most pungent types including chillies
are consumed in very small quantities and are considered as spice or condiment
for seasoning and for stimulating appetite. They are also used industrially as
an ingredient of many products as well as some pharmaceutical products (Grubben
et al., 2004). Pepper is among the
most varied and widely used foods in the world (Dipeolu and Akinbode, 2008). Virtually all countries of the world
produce pepper at different levels and it has been reported to be effective in
repelling insects and other garden pests because of a chemical called capsaicin
(Kathleen, 2010). Capsaicin is the primary substance that controls hotness in
peppers. It irritates the eyes and skin of insects, animals and people and
tastes bad to some pests making the host plant unappealing (Kathleen, 2010).
Pepper has a high amount of alkaloid, capsoicinoid that makes it a necessary
ingredient used for spice commodity in the world (Ashenafi et al., 2013). Pepper as a pest repellant has been used for
generations in home gardens, though until recently it was dismissed by many as
an old folk remedy (Kathleen, 2010).
A
number of control methods have been used to reduce crop losses caused by
insects pests and diseases both in fields and storage. Such control methods
include planting of resistant crop varieties, crop rotation, removal of
volunteer plants and crop debris from harvested fields, use of botanicals both
in fields and stores, use of synthetic chemicals, sex pheromones and
intercropping (Alexander, 1992). These methods are often combined in an
integrated management strategy (Talekar and Pollard, 1991). Some other methods
include the use of natural control agents such as predators, parasitoids,
entomopathogenic bacteria and nematodes (Jansson and Lecron, 1991). Based on
the agricultural system in Nigeria, the farmer’s ability and availability of
control agents and economic limitations, pest control using cultural technique
is considered to be the most appropriate approach, and most likely adopted,
considering the traditional agricultural systems employed by the farmers.
Modification
of certain cultural techniques would be useful and appropriate in changing the farmer’s
production system. Intercropping is among the cultural technique that is
already widely practiced in our locality (Jansson and Lecron, 1991) which could
be considered and integrated with other cultural methods.
1.2 OBJECTIVES OF THE STUDY
Objectives of this study were to:
1. Assess
the effect of intercropping and earthing up on sweetpotato weevil density.
2. Determine
the effect of spacing on the population of Cylas
puncticollis in a sweetpotato/pepper
intercrop.
3. Determine the effect of three sweetpotato
varieties and the time of introduction of component crop (pepper) on the
population of Cylas puncticollis.
4. Determine the effect of intercropping on
growth and yield of sweetpotato
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