ABSTRACT
Two separate field experiments were conducted during 2015 and 2016 cropping seasons at the National Root Crop Research Institute (N.R.C.R.I.) Umudike to evaluate the effect of vegetation residue, crop spacing and weed control methods on the emergence pattern, density of mimosa (Mimosa invisa Mart.) and yields of two cassava varieties of contrasting morpho-types. The sites used for the experiments were predominately infested with M. invisa Mart. The experiments were laid out in split-split plot in randomized complete block design (RCBD) with three replications. For the experiment on the effect of residue and weed control methods on cassava yield, the main plot consisted of two residue management practices (burning and no burning). The sub-plot consisted of two cassava varieties of contrasting morphology (TME 419 - sparse branching variety and NR 8082 - profuse branching variety) and the sub-sub-plot consisted of four weed control methods (hoe weeding at 4, 8 and 12 weeks after planting (WAP), S-metolachlor (1160 g/ha) + atrazine (1480 g/ha) applied pre-emergence followed by hoe weeding at 12 and 16 WAP, S-metolachlor (1160 g/ha) + atrazine (1480 g/ha) applied pre-emergence followed by trifloxysulfuron sodium (8 g/ha) applied post-emergence at 8 WAP and Weedy check). In the experiment on effect of crop spacing and weed control methods on cassava yield, the main plot treatments were three crop spacing; 1 m × 0.6 m, 1 m × 0.8 m, and 1 m x 1 m. The sub-plot treatments were two cassava varieties of contrasting morphology (TME 419 and NR 8082) while the sub-sub-plot treatments were four weed control methods (hoe weeding at 4, 8 and 12 weeks after planting (WAP), S-metolachlor (1160 g/ha) + atrazine (1480 g/ha) applied pre-emergence followed by hoe weeding at 12 and 16 WAP, S-metolachlor (1160 g/ha) + atrazine (1480 g/ha) applied pre-emergence followed by trifloxysulfuron sodium (8 g/ha) applied post-emergence at 8 WAP and Weedy checks). Data collected were subjected to analysis of variance and means separated using least significant difference (LSD). The results obtained showed that hoe weeding at 4, 8 and 12 weeks after planting (WAP), S-metolachlor (1160 g/ha) + atrazine (1480 g/ha) applied pre-emergence followed by hoe weeding at 12 and 16 WAP, and S-metolachlor (1160 g/ha) + atrazine (1480 g/ha) applied pre-emergence followed by trifloxysulfuron sodium (8 g/ha) significantly (P ≤ 0.05) controlled M. invisa density in both cropping seasons at 12 to 16 WAP. At 10 months after planting (MAP) and 2 months after harvesting, significantly higher densities of M. invisa were observed in plots that were hoe weeded at 4, 8 and 12 (WAP) and S-metolachlor (1160 g/ha) + atrazine (1480 g/ha) applied pre-emergence followed by hoe weeding at 12 and 16 WAP whereas, NR 8082 with the highest canopy cover at 1 m x 0.6 m spacing reduced the mimosa seedling emergence and other weeds compared with TME 419. Reduction in plant spacing from 1m x 1m to 1 m x 0.6 m significantly (P ≤ 0.05) reduced weed density, and increased root yield in both cropping seasons whereas residue management methods did not control M. invisa density. Plots treated with S-metolachlor (1160 g/ha) + atrazine (1480 g/ha) applied pre-emergence followed by trifloxysulfuron sodium (8 g/ha) provided the highest return on investment of N209.19 and N616.68 /ha per naira invested in 2015 and 2016 respectively, and effectively controlled M. invisa in the cassava field.
TABLE OF CONTENTS
CONTENTS PAGE
Cover
page i
Title
page ii
Declaration iii
Dedication iv
Certification v
Acknowledgements vi
Table
of Contents vii
List
of Tables ix
List
of Figures xiii
List
of Plates xiv
Abstract xv
CHAPTER
1 INTRODUCTION 1
1.1 Background of the Study 1
1.2 Statement of the Problem 2
1.3 Justification of the Research 3
1.4 Objectives 5
CHAPTER
2 LITERATURE REVIEW 7
2.1 Origin, Classification and Botany of
Cassava 7
2.1.1 Origin and distribution of cassava 7
2.1.2 Classification of cassava 7
2.1.3 Botany of cassava 9
2.2 Importance of Cassava 10
2.2.1 Economic importance of cassava 10
2.2.2 Food and nutrition value of cassava 11
2.2.3 Industrial value of cassava 13
2.2.4 Medicinal value of cassava 14
2.3 Climatic and Edaphic Requirements for
Cassava Production 15
2.4 Effect of Weed Infestation on Cassava
Production 16
2.4.1 Importance of weed in cassava production 17
2.4.2 Effect of burning on weed emergence and
density 19
2.4.3 Effect of crop spacing on weed emergence and
density 21
2.4.4 Effect of earthing up / tillage on weed
emergence and density 22
2.5 Weed Management in Cassava Farms 24
2.5.1 Preventive measures 25
2.5.2 Cultural weed management 26
2.5.3 Mechanical weed control 26
2.5.4 Biological weed control 27
2.5.5 Chemical weed control / The use of
herbicides 27
2.5.6 Integrated weed management (IWM) method 29
2.6 Origin, Classification and Botany of
Giant Sensitive Plant 30
2.6.1 Origin of Giant sensitive plant 30
2.6.2 Classification of Giant sensitive plant 30
2.6.3 Botany of Giant sensitive plant (Mimosa invisa Mart.) 32
2.7 Characteristics of Giant Sensitive Plant 33
2.8 Economic Importance of Giant Sensitive
Plant 34
2.9 Management of Giant Sensitive Plant 35
2.9.1 Physical
and mechanical control 35
2.9.2 Chemical
control 37
2.9.3 Biological
control 38
2.10 Effect
of Environmental Factors and Weed Control Practices on Weed
Growth
and Development in Cropping Systems 40
2.10.1 Effect of rainfall on weed seedling emergence 40
2.10.2 Effect of temperature on weed seedling
emergence 41
2.10.3 Effect of sunlight on weed seedling emergence 42
2.10.4 Effect of plant spacing on crop growth / yield
parameters and weed density 43
2.10.5 Effect of herbicide application on weed seed
germination and density 44
2.10.6 Effect of tillage / hoeing on weed seed bank,
emergence and flora residue
Management 46
2.10.7 Agricultural burning 47
2.10.8 Effect of smoke on weed seed germination,
seedling emergence, and dormancy 48
2.10.9 Effect of crop residue management techniques
on soil and crop yield 48
2.10.10
Integrated weed management (IWM) 51
CHAPTER
3 MATERIALS AND METHODS 53
3.1 Experimental Site 53
3.2 Initial
Weed Flora Composition at the Study Site 53
3.3 Effect of Vegetation Residue Management
and Weed Control
Methods
on Mimosa Seedling Emergence Pattern,
Density and Cassava Yield 54
3.3.1 Land preparation 54
3.3.2 Soil temperature during the burning of
vegetation residues 54
3.3.3 Soil sampling 54
3.3.4 Planting materials, planting, and field
maintenance 55
3.3.5 Experimental design 55
3.3.6 Treatments 55
3.3.7 Field layout 56
3.4 Effect of Plant Spacing and Weed Control
Methods on Mimosa and Yield of
Cassava 56
3.4.1 Land preparation, planting materials,
planting, and field maintenance 56
3.4.2 Experimental design and treatments 58
3.4.3 Treatments 58
3.4.4 Field layout 58
3.5 Data Collection 58
3.5.1 Weed density and biomass 58
3.5.2 Cassava leaf area 60
3.5.3 Cassava stem girth 60
3.5.4 Cassava canopy spread 60
3.5.5 Cassava fresh root yield 60
3.5.6 Mimosa
pod and seed yield (Collected at 7 MAP) 60
3.5.7 Weed population at 2 months after harvest
(i.e. 12 MAP) 61
3.5.8 Economic evaluation of different weed
control methods 61
3.6 Statistical Model and Analysis 62
CHAPTER
4 RESULTS AND DISCUSSION 63
4.1 Results 63
4.1.1 Meteorological data of the experimental site 63
4.1.2 Soil properties of the experimental site 63
4.1.3 Weed composition and relative dominance at
the experimental site 66
4.1.4 Effect of vegetation residue management and
weed control methods on Mimosa
Seedling emergence pattern, density
and cassava yield 66
4.1.4.1
Mimosa invisa density as influenced
by residue management, cassava variety,
and
weed control methods 66
4.1.4.2
M. invisa emergence pattern as
influenced by residue management, cassava
variety
and weed control methods 69
4.1.4.3
Weed dry matter as influenced by residue management, cassava variety, and
weed
control methods 78
4.1.4.4
Mimosa pod and seed yield as
influenced by residue management, cassava
Variety
and weed control methods 80
4.1.5 Effect of vegetation residue management and
weed control management
on
cassava growth and yield 80
4.1.5.1
Height of cassava as influenced by residue management and weed control
methods 80
4.1.5.2
Stem girth of cassava as influenced by residue management and weed control
methods 84
4.1.5.3 Leaf area of cassava as influenced by residue
management and weed control
methods 84
4.1.5.4 Number of leaves of cassava per plant 86
4.1.5.5 Number of cassava stems as influenced by
residue management and weed
control methods 89
4.1.5.6 Cassava root yield as influenced by residue
management and weed control
methods 89
4.1.5.7 Correlation of the growth and yield parameters
of cassava and Mimosa invisa 91
4.1.5.8 Economic analysis of weed control methods for M. inivisa under different
residue management methods 91
4.1.5.9 Composition of weed species after cassava
harvest as influenced by residue
management, cassava variety, and
weed control methods 95
4.1.6 Effect of plant spacing and weed control
methods on Mimosa seedling
emergence,
density and cassava yield 97
4.1.6.1 Effect of spacing, cassava variety, and weed
control methods on Mimosa invisa
density 97
4.1.6.2 Effect of spacing and weed control methods on Mimosa invisa emergence pattern 97
4.1.6.3 Effect of spacing and weed control methods on
total weed dry matter 105
4.1.6.4 Effect of spacing and weed control methods on Mimosa pod and seed yield 108
4.1.6.5 Effect of spacing and weed control methods on
the height of cassava 111
4.1.6.6 Effect of spacing and weed control methods on
stem girth of cassava 111
4.1.6.7 Effect of spacing and weed control methods on
leaf area of cassava 114
4.1.6.8 Effect of spacing and weed control methods on
the leaves of cassava 114
4.1.6.9 Effect of spacing and weed control methods on
canopy spread of cassava 120
4.1.6.10
Effect of spacing and weed control methods on cassava number of stems 123
4.1.6.11
Effect of spacing and weed control methods on cassava root yield 123
4.1.6.12
Effect of spacing and weed control methods on weed species composition at 2
Months after cassava harvest 126
4.1.6.13
Correlation of growth and yield parameters of cassava and Mimosa invisa due
to
plant spacing and weed control methods 129
4.1.6.14
Economic analysis of the weed control methods under different crop spacing 132
4.2 Discussion 134
CHAPTER
5 CONCLUSION AND RECOMMENDATIONS 159
5.1 Conclusion 159
5.2 Recommendations 161
REFERENCES 163
APPENDICES 193
LIST OF TABLES
4.1 Meteorological data of the experimental
site in 2015 and 2016 cropping seasons 64
4.2 The physical and chemical properties of
the experimental site soil in 2015
and
2016 cropping seasons 65
4.3 Weed
composition and relative abundance of weed species of the experimental
site in 2015 and 2016
cropping seasons 67
4.4 Interaction
between residue management and weed control methods on Mimosa
invisa
density at 12 weeks after planting (WAP) in 2015 and 2016 copping
seasons
68
4.5 Interaction
between residue management and cassava variety on Mimosa
invisa
density at 10 months after planting (MAP) in 2015 and 2016 cropping
seasons - 70
4.6 Effect
of residue management, cassava variety and weed control methods on
weed dry weight in 2015
and 2016 cropping seasons
79
4.7 Effect
of residue management, cassava variety and weed control methods on
Mimosa
invisa pod and seed yield at 7 MAP in 2015 and
2016 cropping seasons 81
4.8 Interaction
of residue management, cassava variety and weed control methods
on number of Mimosa seeds at 7 months after planting
(MAP) in 2015 and 2016
cropping seasons 82
4.9 Effect
of residue management and weed control methods on cassava plant height
and stem girth at Umudike
in 2015 and 2016 cropping seasons 83
4.10 Effect
of residue management, cassava variety and weed control methods on
cassava leaf area and
total number of leaves per plant at Umudike in 2015 and
2016 cropping seasons 85
4.11 Interaction
of residue management, cassava variety and weed control
methods on cassava total
number of leaves at 12 weeks after planting (WAP) in
2015 and 2016 cropping
seasons 87
4.12 Interaction
between residue management and weed control methods on cassava
total number of leaves at
12 weeks after planting (WAP) in 2015 and 2016
cropping seasons
88
4.13 Effect
of residue management, cassava variety and weed control methods on
cassava number of stems
per stand and cassava yield (t/ha) at harvest from
2015 and 2016 cropping
seasons
90
4.14 Correlation
coefficient of growth and other yield parameters of cassava and
Mimosa
in 2015 cropping season 92
4.15 Correlation
coefficient of growth and other yield parameters of cassava and
Mimosa
in 2016 cropping season 93
4.16 Effect
of weed control methods on returns on investment in cassava root
tuber yield in 2015 and
2016 cropping seasons 94
4.17 Class of
weed species at the experimental site and their level of infestation at
2 months after cassava
harvesting 96
4.18 Plant
spacing and cassava variety interaction effect on Mimosa invisa density
12 WAP in 2015 and 2016
cropping seasons 98
4.19 Cassava variety and
weed control method interaction effect on Mimosa
density 10 months after planting (MAP) in 2015 and 2016 cropping
season 99
4.20 Effects
of plant spacing, cassava variety and weed control methods on total
weed dry weight in
cassava field in 2015 and 2016 cropping seasons at
Umudike 107
4.21 Effect
of plant spacing, cassava variety and weed control methods on Mimosa
number of seeds and dry
weight and pod dry weight at 7 MAP in 2015 and 2016
cropping seasons at
Umudike 109
4.22 Interaction
effect of cassava variety and weed control methods on Mimosa
pod dry weight, seed dry
weight and number of seeds at 7 months after planting
(MAP) in 2015 and 2016
cropping seasons at Umudike 110
4.23 Interaction
effect of plant spacing, cassava variety and weed control methods
on number of Mimosa seeds 7 months after planting in
2015 and 2016 cropping
seasons at Umudike 112
4.24 Effect
of plant spacing, cassava variety and weed control methods on cassava
plant height and stem
girth in 2015 and 2016 cropping seasons
at Umudike 113
4.25 Effect
of plant spacing, cassava variety and weed control methods on cassava
leaf area and total
number of leaves per plant at 8 and 12 weeks after
planting (WAP) in 2015
and 2016 cropping season at Umudike
115
4.26 Effect
of plant spacing and cassava variety interaction on cassava leaf area
At 8 and 12 weeks after
planting (WAP) in 2015 and 2016 cropping seasons at
Umudike
116
4.27 Effect
of plant spacing and cassava variety interaction on cassava number of
leaves per plant at 8 and
12 weeks after planting (WAP) in 2015 and 2016
cropping seasons at
Umudike 118
4.28 Effect
of cassava variety and weed control methods interaction on cassava
number of leaves 8 and 12
weeks after planting (WAP) in 2015 and 2016
cropping seasons at
Umudike 119
4.29 Effect
of plant spacing, cassava variety and weed control methods interaction
on cassava number of
leaves per plant at 8 and 12 weeks after planting (WAP)
in 2015 and 2016 cropping
seasons at Umudike 121
4.30 Effect
of plant spacing, cassava variety and weed control methods on cassava
number of branches and
canopy spread per plant at 8 and 12 WAP in 2015
and 2016 cropping seasons
at Umudike 122
4.31 Effect
of plant spacing and cassava variety interaction on cassava canopy
spread 12 weeks after
planting (WAP) in 2015 and 2016 cropping
seasons at Umudike 124
4.32 Effect
of plant spacing, cassava variety and weed control methods on number
of cassava stems per
stand and cassava fresh root yield at 10
months after
planting in 2015 and 2016
cropping seasons 125
4.33 Effect
of plant spacing, cassava variety and weed control methods interaction
on cassava fresh root
yield at 10 months after planting (MAP) in 2015 and 2016
cropping seasons 127
4.34 Class of
weed species at the experimental site and their level of infestation 2
months after harvesting
of cassava in 2015 and 2016 cropping seasons 128
4.35 Correlation
coefficient of growth and other yield parameters of cassava and
Mimosa
at 12 WAP in 2015 cropping season at Umudike 130
4.36 Correlation
coefficient of growth and other yield parameters of cassava and
Mimosa
at 12 WAP in 2016 cropping season at Umudike
131
4.37 Effect
of weed control methods on return on investment in cassava root
yield in 2015 and 2016 cropping seasons 133
LIST
OF FIGURES
3.1 Field Layout for effect of vegetation
residue management and weed control
methods
on Mimosa seedling emergence pattern, density and cassava yield 57
3.2 Field Layout for effect of plant spacing
and weed control methods on Mimosa
seedling emergence pattern, density and cassava yield 59
4.1 Effect of residue management on M. invisa emergence pattern in 2015
and 2016 71
4.2 Effect of cassava variety on M. invisa emergence pattern in 2015 and
2016
cropping seasons 72
4.3 Effect of weed control methods on M. invisa emergence pattern in 2015 and
2016 cropping seasons 74
4.4 Effect of weed control methods on
emergence pattern of class of weeds at 12
WAP in 2015 and 2016 cropping seasons 76
4.5 Effect of weed control methods on
emergence pattern of class of weeds at
10 MAP 77
4.6 Effect of plant spacing on M. invisa emergence pattern in 2015 and
2016
cropping seasons 100
4.7 Effect of cassava variety on M. invisa emergence pattern in 2015 and
2016
cropping season 102
4.8 Effect of weed control methods on M. invisa emergence pattern in 2015 and
2016 cropping seasons 103
4.9 Effect of weed control methods on
emergence pattern of class of weeds at 12
WAP in 2015 and 2016 cropping seasons 104
4.10 Effect of weed control methods on emergence
pattern of class of weeds at 10
MAP in 2015 and 2016 cropping seasons 106
LIST
OF PLATES
2.1 Thicket of Mimosa invisa Mart. plant 31
CHAPTER
1
INTRODUCTION
1.1 BACKGROUND OF THE STUDY
Cassava
(Manihot esculenta Crantz), which originated from Amazonia, is a tropical,
perennial, woody shrub of the Euphorbiaceae family grown mainly for its edible roots
rich in starch (Lokko et al., 2007; Howeler
et al., 2013). Globally, this
tropical root crop is regarded as the sixth most important crop after wheat (Triticum aestivum), rice (Oryza sativa), maize (Zea mays), potato (Solanum tuberosum), and barley (Hordeum
vulgare) (Lebot, 2009; Prochnik
et al., 2012).
In the tropics, it is the
third most important source of calories, after rice and maize (Okogbenin et al., 2013). In Africa, about 88 percent of its production is
consumed by humans and the remainder used for animal feed mixtures and production
of starch-based products (starches and alcohol) by industries (Henry et al.,
1998; Plucknett et al., 2000; Adelekan, 2010). In Nigeria, it is regarded
as not only an important food crop, but also a major source of income for both subsistent
and commercial cassava farmers. Furthermore,
it is an important source of industrial starch (Ihemere et al., 2008). According to Howeler et al. (2013), its root starch can be used in a wide array of
industries, such as food manufacturing, textiles, pharmaceuticals, plywood, adhesives
and paper, feedstock and for the production of ethanol (biofuel). Its production level as of 2016 was
estimated at 59,565,916 metric tonnes per hectare (t/ha) in Nigeria alone (FAO,
2018). The roots are consumed freshly boiled after soaking it in water or processed
into a wide variety of granules, pastes and flours whereas the leaves are
consumed as a green vegetable in some parts of Africa and Brazil since they
provide protein and vitamins A and B, and can also be sold as dried (leaf)
products in Tanzania (COSCA, 1996; Hillocks, 2002).
However, the production
of cassava (M. esculenta) is faced
with numerous constraints in Africa and Nigeria in particular. Although the
crop has the potential to produce / store more carbohydrate than any other
major important grain and root crops, it typically fails to reach that
potential due to factors such as poor-quality planting material (cuttings),
sub-optimum agronomic practices, pests and diseases (Fermont, 2009; Jarvis et al., 2012). Weeds, pests and diseases
are generally considered to be the most important constraint to cassava
production (Hillocks, 2002; Jarvis et al.,
2012). Among these three major factors mentioned, weed interference is the most
critical since the crop is a poor competitor and usually suffer serious yield
loss if not adequately weeded during the early stages of the plant growth
(Tongglum et al., 1992; Howeler et al., 2013). According to Howeler et al. (2013), the first four months
after planting are most critical for cassava growth as it can easily be overwhelmed
by competition from broad-leaf and narrow-leaf grass weeds. Weeds generally are
often a more severe cassava production constraint than insect pests or diseases
in the field and can reduce root yields by about 50 – 90 percent (Makinde
et al., 2007; FAO, 2014). In Nigeria,
most farmers especially women and children spend more time on weeding than on
any other aspect of crop production (Pypers et al., 2011). Among
the weeds known to cause serious production constraint and reduction in the
yield of cassava is the giant sensitive plant (Mimosa invisa Mart.) (Alabi
et al., 2001; 2004; Lebot, 2009;
Gbadamosi, 2015).
1.2 STATEMENT
OF THE PROBLEM
M. invisa is
a perennial, thorny, scrambly and leguminous weed of neo-tropical shrub which produces
large quantities of seeds at an early age and has a persistent seed bank
(Barneby, 1991; Ekhator et al., 2013). Although it is used in the Philippines to restore
soil fertility in farming systems of reduced or short fallow periods
(establishment of seasonal fallows between harvesting and planting seasons), it
has become an invasive and noxious weed that can take over native vegetation
and form large swathes of dense prickly usually difficult-to-remove stands
(Burgers and William, 2000; MacLean et al., 2003). M. invisa has
a hard or tough impermeable seed which allows some seeds to remain viable and dormant
in the soil for a very long time (Melifonwu, 1994 a, b). It has all-year-round periodic dormancy breakage, germination and
seedling emergence pattern under favourable moist, but not flooded, soil
condition with most germinations occurring at the start and end of the wet
seasons, representing the critical periods of the weed’s interference in crop
fields (Parsons and Cuthbertson, 1992). The periodic seed dormancy breakage / germination
and seedling emergence pattern of the weed
makes long-term effective control measures on a long-cycle crop like
cassava difficult. Consequently, it has become a major problem weed of economic
importance in most cassava fields in Nigeria (Melifonwu, 1994 b; Alabi et al., 2001; 2004; Lebot, 2009), and
its infestation of cassava field has been found to reduce the root yield by 80%
(Alabi et al., 2001). It has also
been reported to disturb the cassava harvest as well as lower the quality of
the stems (Lebot, 2009). It would appear, therefore, that any Mimosa control measure that could
achieve a long-term effect must consider, among other things, factors that
affect its seed germination and seedling emergence, and time of intervention of
the control measures.
1.3 JUSTIFICATION
OF THE RESEARCH
Several weed control methods
such as hand weeding, mechanical weeding, use of herbicides, cover cropping,
and mixed cropping, burning of slashed vegetation residue, mulching with plant
residues, etc. individually and in combinations (integrated weed management)
have been used to control this weed (Chikoye et al., 1999; Chikoye, 2000; Melifonwu et al. 2000; Ekeleme, 2013; Dan et
al., 2016). Yet, the weed kept multiplying and colonizing more cassava
fields in Nigeria to the extent that many farmers tend to avoid fertile arable
lands suitable for cassava production that are infested with M. invisa (Alabi et al., 2004; Ekhator et al.,
2008; APFISN, 2010; Aigbokhan et al.
2010). The hand weeding and mechanical control of Mimosa have been reported to be effective, but full of drudgery, laborious
and difficult (Ehkator et al., 2013).
Burning of dried vegetative parts of the weed and other weeds during the dry
season as a way of controlling the weed and land preparation promoted the
germination of its seeds (Baker and Tery, 1991; Jayasree, 2005). Digging,
removal of Mimosa and ploughing twice
a year and weeding with sickle (knife) at monthly intervals produce
significantly better results than flaming at the dry season alone in the
control of the weed (Jayasree, 2005). Application of 2,4-D herbicide was not
effective in the control of the weed whereas paraquat temporally controlled it
but glyphosate effectively controlled the weed (KAU, 2003). Atrazine, diuron,
flupchloralin, metolachlor, and pendimethalin as pre-emergence herbicides,
effectively controlled Mimosa seed
germination whereas alachlor, butachlor, pretilachlor, and oxyfluorfen did not
control the weed (Jayasree,
2005). Therefore, Melifonwu et al. (2012) recommended application of atrazine and primextra
(s-metolachlor 290 g/L + atrazine 370 g/L) at 2.0 and 2.5 kg a.i./ha followed
by hand weeding at 12 WAP to effectively control the weed. The use of
bio-agents (biological control) such as certain insects and fungi which had
been used to control the weed in Brazil, Australia, and several Pacific Islands
is yet to be studied and evaluated in Nigeria (Ekhator et al., 2013).
The increasing cost and
difficulty associated with M. invisa control
make it necessary to adopt or evolve sustainable management strategies that can
reduce the labour requirement required to manage the weed (Ekeleme et al., 2003). As weed control methods
attempt to limit the deleterious effect of weeds growing with crop plants,
understanding the biology and growth habits of weed species, as well as the
crop plants, is critical to formulating effective weed management on farms (Adigun,
1984).
Field observation has shown
extensive Mimosa seedling flushes in fields
where dry Mimosa vegetative residues were
burnt than where they were not; suggesting that Mimosa seed dormancy could be broken by high temperatures generated
from burning dry vegetative residues in Mimosa
infested fields. Therefore, imposing
seed scarifying conditions during land preparation such as vegetation burning
could be an important factor in depleting the soil seed bank of the weed (Baker
and Tery, 1991; Sanchez et al., 2003;
2005). This in conjunction with optimal cropping systems
(use of cassava of ideal morphological characteristics and spacing) and correct
timing of intervention measures (herbicide application and /or hoe weeding)
could prove satisfactory management of the weed in both large- and small-holder
cassava farms (Jayasree, 2005;
Melifonwu et
al., 2012).
Previous studies on the
control of Mimosa in Nigeria appear
to have focused on short-term control of this weed in cassava fields neglecting
the long-term control methods. Therefore, there is need to study the effect of
residue management practices, selected weed control methods, crop spacing and
cassava varieties on M. invisa in
order to develop weed management methods for long-term effective control of Mimosa in a cassava farming system and
underscore the dynamics of weed species in response
to different weed control methods after harvest.
1.4
OBJECTIVES:
The
objectives of this study were to;
1. investigate
the effect of two residue management practices (burning and non-burning) on the
emergence pattern and density of Mimosa
invisa in cassava farms.
2. evaluate
the impact of crop spacing on the emergence pattern and density of Mimosa in cassava farms.
3. evaluate
the effect of weed control methods (Hoe weeding, pre-emergence herbicide
application followed by hoe weeding, and chemical control) on M. invisa emergence pattern and density
in cassava fields.
4. assess
the effect of two cassava varieties of contrasting morphology (profuse
branching and sparse branching) on the emergence and density of Mimosa seedling and other weed species
in cassava farms.
5. evaluate
the combined effect of residue management, cassava variety and weed control
methods on the emergence and density of Mimosa,
and yield of cassava.
6. evaluate
the combined effect of crop spacing, cassava variety, and weed control methods
on the emergence and density of Mimosa,
and yield of cassava.
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