ABSTRACT
The first experiment involved nine improved cowpea genotypes and a local variety. The ten treatments were planted in two locations, namely the Research Farm of the College of Agriculture, Mgbakwu in Anambra State (060 17ʹN, 070 04ʹE; 83m asl) and the Experimental Farm of the Federal College of Agriculture, Ishiagu in Ebonyi State (050 58ʹN, 070 34ʹE; 197 m asl), over a period of two years and two seasons per year in each of the two locations. The experiment was spilt-plot arranged in randomized complete block design (RCBD) with three replications. The second experiment was conducted at the DEMACCO Integrated Farms Ltd., Ako, Nike in Enugu State (060 34ʹN, 070 35ʹE; 154 m asl). The experiment consisted of four promising genotypes selected from experiment one and a local variety used as check. An open pollinated maize variety (ACR9931) was intercropped with the five cowpea genotypes. The maize and cowpea genotypes were sown over a period of two years and two seasons in each year. The experiment was split-split plot arranged in RCBD with three replications. A total number of twenty nine parameters were sampled consisting of eleven growth, twelve grain yield and six insect pest damage components. Data were subjected to analysis of variance (ANOVA) using the GENSTAT, 2003 edition. Differences among treatment means were compared using F-LSD, while interaction of genotype by environment, genotype by traits and environment by traits were computed using GGE biplot analytical model. This study revealed the presence of genotype X season, genotype X insect protection and genotype X season X insect protection interaction for experiment one, while experiment two indicated the presence of genotype X season, genotype X cropping system, genotype X spray regime and genotype X season X cropping system X spray regime interaction. Growth, reproductive, grain yield and insect damage components were highly significant in all the environments. Yield and yield components were significantly higher in early season than in late season. Similarly, plant population and cowpea biomass were higher in early than late season. Pod length, number of seed per pod, number of branches and number of internodes were least influenced by the environments due to their high heritability. In all the environments, seed size was significantly higher in IT97K-277-2, IT97K-556-4 and IT93K-452-1, than the rest genotypes, while IT84S-2246-4 and IT90K-82-2 consistently expressed significantly lower seed size. The local variety produced significantly higher seed size than all the test genotypes when sprayed with insecticide in late season. The genotypes IT90K-277-2, IT97K-556-4 and local variety exhibited dual-purpose (grain and fodder) characteristics, while the rest genotypes were purely grain type. Most of the dual-purpose cowpeas are both indeterminate and long duration. The short growth duration and higher mean grain yield made IT93K-452-1 the best grain type cowpea because it combined these qualities with tolerance to most post flowering pests. The genotype IT93K-452-1 also produced reasonable grain yield in late season without chemical spray. IT98K-131-2 was an outstanding medium maturing genotype combining superior grain yield attribute with tolerance to both pre-and-post flowering pests in all the environments. Furthermore, this variety also produced satisfactory grain yield in late season without insecticide application. Genotype IT97K-556-4 on the other hand, harboured the highest population of most pests sampled in all the environments. This study further showed that thrips, Maruca, pod sucking bugs and bruchids were the most prevalent insect pests of cowpea in south eastern Nigeria, while aphids and Ootheca were the minor pests. Application of insecticides once each at flower bud initiation, full bloom and podding significantly reduced insect pest population and increased grain yield of cowpea significantly. Improved cowpea genotypes recorded significantly higher grain yield than the local check in all the environments. Medium to late maturing genotypes were better adapted to late season while early maturing genotypes performed well in both seasons. Bruchids, Maruca, pod sucking bugs and thrips were more abundant in late season than early season while aphids and Ootheca population were more widespread in early season than late season. Brown seeded cowpea genotype consistently harboured lower infestation by bruchids than white seeded types. This study also showed that insecticide treatment targeted at the critical growth stages especially at 50 percent podding and early sowing significantly reduced bruchids damage on stored cowpea seed. Grain yield loss assessment was negligible in early season for all the genotypes while in late season it was 100 percent for local variety, 34 percent for best yielding medium maturing genotype (IT98K-131-2) and 30 percent for best yielding early maturing genotype (IT93K-452-1). Percentage reduction in insect population when 3 sprays were applied relative to zero spray for aphids, bruchids, Maruca, Ootheca, pod sucking bugs and thrips are 121 percent, 240 percent, 174 percent, 45 percent, 38 percent and 270 percent respectively. Intercropping reduced dry fodder yield in early season by 22 percent and in late season by 41 percent. On the other hand, intercropping did not significantly reduce number of branches, internodes number, number of leaves, number of nodules, plant population, and root length. Meanwhile, peduncle length was significantly reduced by intercropping in both early and late season but varied widely among the genotypes tested, with local cowpea variety being most affected. Peduncle length in cowpea was obviously sensitive to stress imposed by intercropping particularly in late season and could be used as an index for determining cowpea cultivars adapted to intercropping environment. Intercropping in both seasons significantly reduced yield and yield components in cowpea but more in late than early season. Consequently, intercropping reduced grain yield in early season by 14 percent while in late season it reduced it by 25 percent. Also, intercropping in early season reduced days to maturity but did not affect 50 percent bloom and pod filling duration. However, in comparison with early season, all the genotypes in late season flowered and matured earlier, while on the contrary they took longer days to fill their pods. In both seasons, sole cropping generally produced higher grain yield than intercropping when sprayed with insecticide. Conversely, cowpea grain yield in intercropping were generally higher than yields from sole cropping when no insecticide was applied, suggesting less insect damage under intercropping. Early maturing genotypes produced significantly higher grain yield in early and late seasons and in both sole and intercropping, while medium and late maturing genotypes expressed their highest yield potentials in sole cropping in late season. Also, in late season, intercropping significantly reduced the population of bruchids, pod sucking bugs and thrips but did not affect the population of the rest insect pests. Highest grain yield components were realized in genotypes grown in intercropping with two sprays while in sole cropping early maturing genotypes required two sprays while medium and late maturing genotypes required three sprays to produce the highest grain yield. Late season planting reduced the population of aphids, Maruca and Ootheca by 122 percent, 183 percent, and 47 percent respectively, while early season sowing reduced the population levels of pod sucking bugs by 47 percent and thrips by 104 percent. Intercropping reduced the population of aphids, bruchids, pod sucking bugs and thrips by 40 percent, 9 percent, 8 percent, and 100 percent respectively. Meanwhile, intercropping increased the infestation of Maruca by 9 percent while Ootheca was unaffected by cropping system. Intercropping combination of ACR9931/IT98K-131-2 had positive effects on maize through the production of significantly higher yield and yield components of maize, while ACR9931/Local combination depressed components of maize yields. We found improved medium maturing, indeterminate cowpea cultivar with long peduncle length as most suitable for use in intercropping with maize in South-eastern Nigeria. Maize performed better under intercropping than sole cropping in early than in late season, in 2009 than 2010. The yield reduction in maize from cropping system, season and year effects was caused by decline in cob length, cob weight, number of cobs per plot, seed weight, 100 seed weight and harvest index, and not by number of plant stands. This revealed that maize productivity is more influenced by these traits.
TABLE OF CONTENTS
Title
Title Page                                           ……               ……               ……                           i
Certification                                       ……               ……               ……                           ii
Dedication                                         ……               ……               ……                           iii
Acknowledgement                             ……               ……               ……                           iv
Table of Contents                              ……               ……               ……                           vi
List of Tables                                     ……               ……               ……                           xi
List of Figures                                    ……               ……               ……                           xiv
Abstract                                             ……               ……               ……                           xvii
Introduction                                      ……               ……               ……                           1
Literature Review                            ……                ……               ……                           5
2.1      Origin and distribution of cowpea     ……               ……                           5
2.2      Soil and nutrient requirement            ……               ……                           6
2.3      Climatic requirement  ……               ……               ……                           7
2.4      Cowpea insect pests   ……               ……               ……                           8
2.4.1   Aphids                                   ……               ……               ……                           8
2.4.2   Pod bugs                    ……               ……               ……                           9
2.4.3   Thrips                         ……               ……               ……                           10
2.4.4   Pod borers                  ……               ……               ……                           10
2.4.5   Beetles                                   ……               ……               ……                           11
2.4.6   Bruchids                     ……               ……               ……                           13
2.5      Pest management philosophy             ……               ……                           13
2.6      Host plant resistance  ……               ……               ……                           14
2.7      Chemical control        ……               ……               ……                           15
2.8      Post harvest storage   ……               ……               ……                           16
2.9      Cultural practices and control            ……               ……                           17
2.10    Intercropping             ……               ……               ……                           23
2.11    Varieties adapted to intercropping system                ……                           24
2.12    Cowpea haulms as fodder for livestock                    ……                           25
2.13    Genotype by environment interaction ……              ……                           26
2.14    Genotype and genotype by environment (GGE) biplot                                28
Materials and Methods                     ……               ……              ……                           30
3.1 Â Â Â Â Â Genotype, soil and weather description and characterization
of the experimental sites …              ……               ……                          30
3.1.1   Genotype description ……               ……               ……                           30
3.1.2   Soil characterization   ……               ……               ……                           30
3.1.3   Weather description   ……               ……               ……                           32
3.2      Experiment one          ……               ……               ……                           35
3.2.1   Experimental sites      ……               ……               ……                           35
3.2.2   Sowing dates             ……               ……               ……                           35
3.2.3   Experimental design, treatments and treatment allocation..                          35
3.2.4   Cultural operations     ……               ……               ……                           36
3.2.5   Data collection           ……               ……               ……                           36
3.2.6   Statistical analysis     ……               ……               ……                           38
3.3      Experiment two         ……               ……               ……                           38
3.3.1   Experimental sites      ……               ……               ……                           38
3.3.2   Sowing dates             ……               ……               ……                           38
3.3.3   Experimental design, treatments and treatment allocation..                          38
3.3.4   Cultural practices       ……               ……               ……                           40
3.3.5   Data collection           ……               ……               ……                           40
3.4      Statistical analysis      ……               ……               ……                           41
Results                                              ……               ……   ……   ……                          42
4.1Â Â Â Â Â Â Test of significance of growth, reproductive, grain
yield and yield components and insect damage responses    ……               42
4.2Â Â Â Â Â Â Main effect of genotype on growth, reproductive,
grain yield and insect pest damage component
in early and late season combined in Ishiagu, 2007   ……   ……               48
4.3Â Â Â Â Â Â Main effect of genotype on growth, reproductive, grain
yield and insect pest damage component in early and late
season combined in Ishiagu, 2008     ……   ……   ……   ……               54
4.4Â Â Â Â Â Â Main effect of genotype on growth, reproductive grain
yield and insect damage components in early season,
combined over 2007 and 2008, Ishiagu .…… ……   ……   ……              56
4.5Â Â Â Â Â Â Main effect of genotype on growth, reproductive, grain
yield and insect damage components in late season
combined over 2007 and 2008 in Ishiagu. .…… ……  .…… ……              61
4.6Â Â Â Â Â Â Â Main effect of genotype on growth, reproductive, grain
yield and insect pest damage component in early and late
season combined in Mgbakwu, 2007.  .…… ……   ……   .……             66
4.7Â Â Â Â Â Â Main effect of genotype on growth, reproductive, grain
yield and insect damage components in early and late
season combined in Mgbakwu, 2008 .…… ……  ……   …….              73
4.8Â Â Â Â Â Â Genotype main effect for growth, reproductive, grain
yield and insect damage components early season
combined over 2007 and 2008, Mgbakwu  …….   ……     ……..             78
4.9Â Â Â Â Â Â Genotype main effect for growth, reproductive, grain
yield and insect pest damage components late season
combined over 2007 and 2008 in Mgbakwu …….  ……   ……..             83
4.10 Â Â Â Interaction effects of year, season and location on
genotype performance for some selected growth,
reproductive and grain yield traits (Performance
of genotype in each environment)-Experiment one   ……   ……..             89
4.11Â Â Â Â Genotype by trait (GXT) relationship combined over
Ishiagu and Mgbakwu for 2007 and 2008 (Experiment one) ……..             99
4.12Â Â Â Â Performance of genotypes across environments (GXE)
for insect damaged components (Experiment one)   ……   ……..             99
4.13 Â Â Â Genotype by insect damaged traits (GXT) across 2007
and 2008 (Experiment one)   ……   ……   …….  ……   ……..             111
4.14Â Â Â Â Â Interaction effects of spray regime and season on
performance of genotype for some selected growth,
reproductive and grain yield components (Experiment one)Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â 111
- Main effect of genotypes combined over 2009 and
2010 in Ako location (Experiment two) …….  ……..    ……….                122
4.16Â Â Â Â Cropping system and genotype effects in early season
combined over 2009 and 2010 ……..   …..…        …………..                 124
4.17Â Â Â Â Cropping system and genotype effects in late season
combined over 2009 and 2010 ……..   ………      ………….                  127
4.18    Season by genotype effect combined over 2009 and 2010 ……                  134
4.19Â Â Â Â Interaction effects of year, season and cropping system
on the performance of genotypes for some selected growth,
reproductive and grain yield components in
Ako location (Experiment two)         ……   ……   ……   ……              137
4.20Â Â Â Â Genotype by trait (GXT) relationship across 2009
and 2010 for growth, reproductive and grain yield components
(Experiment two)…   …    ……      ……      ……            ……              143
4.21Â Â Â Â Interaction effects of year, season and cropping system
on the performance of genotypes for some selected insect
damaged traits (Experiment two)      ……   ……   ……   ……               143
4.22Â Â Â Â Genotype by trait (GXT) relationship across 2009 and
2010 for insect damaged components           (Experiment two) ………                 151
4.23 Â Â Â Barchart showing the effects of spray regime, genotype,
cropping system, season, year, insect pests on grain
yield and insect pest population in Ako location ……  ……….                  157
4.24Â Â Â Â The main effect of maize/cowpea intercropping
on maize growth, reproductive and grain yield components
combined over 2009 and 2010 in Ako ……    ……… ………                168
- Season and genotype effects on growth, reproductive
and grain yield of maize variety combined over 2009
and 2010 in Ako        ……               ……               ……                           168
Discussion                                         ……               ……               ……                          171
5.1      Test of significance for variance component             ……                           171
5.2      Seasonal effects         ……               ……               ……                           172
5.2.1   Plant traits                  ……               ……               ……                           172
5.2.2   Genotypes                  ……               ……               ……                           175
5.2.3   Insect pest components                      ……               ……                           181
5.2.3.1 Aphids                                   ……               ……               ……                           181
5.2.3.2 Bruchids                     ……               ……               ……                           182
5.2.3.3 Ootheca                      ……               ……               ……                           183
5.2.3.4 Pod sucking bugs       ……               ……               ……                           184
5.2.3.5 Maruca                       ……               ……               ……                           185
5.2.3.6 Thrips                         ……               ……               ……                           187
5.3      Insecticides spray regime effects       ……              ……                           187
5.3.1   Growth, reproductive and grain yield components   ……                           187
5.3.2   Insect pest’s management      ……   ……              ……                          190
5.4      Cropping system effects                    ……               ……                           191
5.4.1   Cowpea genotypes and plant traits    ……               ……                           191
5.4.2   Insect pest infestation ……               ……               ……                           194
5.5Â Â Â Â Â Â Cropping system X season X spray regime X
genotype interactions ……               ……               ……                           195
5.6 Â Â Â Â Â Cropping system X season interaction
on maize productivity ……               ……               ……                           197
Conclusion and Recommendations   ……   ……              ……                           199
References                            ……               ……               ……                           205
Appendices                            ……              ……               ……                           238
CHAPTER ONE
INTRODUCTION
Cowpea is cultivated on at least 12.5 million hectares, with an annual production of over 3 million tonnes world wide. Cowpea is widely distributed throughout the tropics, but Central and West Africa accounts for over 64 percent of the area. In West Africa, a substantial part of the cowpea production comes from the drier regions of northern Nigeria (Singh et al., 1997). Mortimore (1980) reported that by the 1960s and 1970s there was a long established cowpea trade network, linking the producing areas in northern Nigeria with the major centers of demand in the south. In other words, cowpea remains predominantly a crop of drier areas. Quin (1997) noted that as further advances are made in crop improvement and management, there will be opportunities for commercial production of cowpea in longer season, wetter agro-ecologies. Furthermore, Kormawa et al. (2002) observed that if suitably adapted improved varieties of cowpea along with appropriate integrated management packages are identified the crop’s production area will expand rapidly to wetter regions.
Cowpea is consumed by humans in many forms; the young leaves, green pods, and green seeds are used as vegetables; dry seeds are used in various food preparations; and the haulms including pod walls are fed to livestock as nutritious supplement to cereal fodder (Barrett 1987). Nigeria is the largest consumer of cowpea in the world (Nnanyelugo et al., 1985; McWatters et al., 1990). Nnayelugo et al. (1997) stated that cowpea consumption in southeastern Nigeria has increased in frequency and quantity by 150 percent and has also reduced severe malnutrition in children by 70 – 100 percent. The image of cowpea has improved and it is being introduced into children’s diets at earlier ages in both rural and urban areas, and that almost all the dry cowpea seeds consumed in southern Nigeria are brought in from the northern part of the country. Similarly, Uguru (2008) is in support of this observation. Although southeastern Nigeria has favorable weather and soil that can sustain commercial grain cowpea production, the region  unfortunately accounted for only about 0.57 percent of the total grain cowpea production and 0.38 percent of the total area cultivated in Nigeria in 2007 (APS, 2008).
The bulk of the diet of rural and urban poor African people consists of starchy food made from cassava, yam, cocoyam, millet, sorghum, and maize. The addition of even a small amount of cowpea ensures the nutritional balance of the diet and enhances the protein quality by the synergistic effect of high protein and high lysine from cowpea and high methionine and high energy from the cereals. The nutritious and balanced diet ensures good health and enables the body to resist infectious diseases and slow down their development (Nielsen et al., 1993). It has been found that HIV/AIDs patients placed on daily cowpea diets experienced significant boost in their immunity level thus prolonging their lifespan (Clark, 2005). Similarly, Carper (1988) pointed out that a cup of cooked, dry beans every day should lower the low-density lipid cholesterol, regulate blood sugar and insulin, lower blood pressure, regulate the bowels, and prevent gastrointestinal troubles, even hemorrhoids and cancer of the gut. Furthermore, individuals with type 1 diabetes can cut their insulin requirements by 38 percent if they increase their bean intake a cup (about 184 g) a day. It is estimated that cowpea supplies about 40 percent of the daily protein requirements to most of the people in Nigeria (Muleba et al., 1997).
Insect pest damage is a major constraint to cowpea production in Nigeria (Raheja, 1976; Amatobi, 1994). Insect pest attack in cowpea often leads to total yield loss (Singh and Allen, 1980; Jackai et al., 1985). Use of insecticides improves the yield of cowpea ten fold (Singh and Allen, 1980; Parh, 1993). Jackai (1983) and Adalla (1994) observed that in parts of Asia the effects of misuse of insecticide is already being felt as more cases of resistance and damage to ecosystems are being reported yearly. Edwards (1993) warned that unless this trend is reversed in Nigeria, we can expect the same problems of the insecticide treadmill that characterizes agricultural systems in the developed world. To increase the efficiency of insecticides and reduce overuse, chemical application should be carefully managed to coincide with critical growth stages where pest pressure is high (Alghali, 1992). In order to reduce insect damage, increase cowpea productivity, and control indiscriminate use of insecticides, it is important to conduct studies to determine the growth stages at which minimum use of insecticide is advisable. Moreover, application of insecticides should be integrated with other cultural practices to increase effectiveness and reduce over use of insecticides (Kamara et al., 2009). There is therefore the need to develop a robust pest management package for cowpea production in Nigeria especially in a pest endemic region like southeastern Nigeria. Afun et al. (1991) stated that cost effectiveness of minimum insecticide applications in combination with other cultural practices show a 50 percent reduction in production cost.
Planting date has been identified as an important component of integrated pest management practices ((Hall, 1992). It has been suggested that adjusting planting dates could cause asynchrony between crops and insect pests (Pedigo, 1989). Karungi et al. (2000) reported that planting early in the season reduced aphids, thrips and pod-sucking bug’s infestation but increased Maruca infestation in Uganda. The reduction in aphids, thrips and pod bugs was attributed to lower population in the early season, which could build up as the season progresses and cause more damage to lately planted cowpea. It was suggested that differences in planting dates could be explored in different agro-ecologies as it may have some potential in influencing the incidence of various insect pests (Taylor, 1978; Akingbohungbe, 1982).
Intercropping has long been known to be a major component of integrated pest management (IPM) (Olufajo and Singh, 2002). Singh and Emechebe (1998) found that intercropped cowpea gave higher grain yields than yields from the sole crop when no insecticide was applied, indicating less insect damage under intercropping. Blade et al. (1997) noted that the local cowpea varieties are highly adapted to intercropping systems than improved varieties but they have a very low harvest index. However, Singh and Emechebe (1998) identified good performance of a number of IITA improved varieties under both sole and intercropping. These cultural practices when combined with the use of insecticides and host-plant resistance are probably the most effective measure against some of the cowpea pests, and could be used as cost effective components of integrated pest management package (Javaid et al., 2005). However, there is no properly packaged IPM program for cowpea production in southeastern Nigeria yet. This is because the individual components have to be developed first before they can be consolidated into a management package. This is part of what this experiment seeks to establish.
Despite the high potential benefits of cowpea in Nigeria, the yield levels are very low which range from 240-300kg/ha (Rachie, 1985). Meanwhile, when the crop is grown in pure stand with required inputs, improved varieties, and appropriate management practices, yield as high as 4 tonne per hectare has been reported (Rachie, 1985; Huxley and Summerfield, 1976; Singh, et al., 2002).
Although different categories of improved cowpea varieties are available on the shelf in the research stations of IITA, there is limited study on the productivity of these varieties in Southeastern Nigeria with respect to their performance or responses when exposed to the entire pest complex under natural field infestation (either sprayed or not sprayed with insecticides) and at different planting dates. The identification of cultivar(s) that produce reasonable yield without insecticidal protection can be a low input approach to solving the problem of yield constraints in cowpea occasioned by high population of insect pests in the region, and also enhance the promotion of sound ecologically and economically viable cowpea production options. Furthermore, the integration of these selected low input genotypes with appropriate sowing date and cropping system will even result in more sustainable cowpea production system through better IPM strategy. Such IPM package would be compatible with resource poor cowpea farmers and equally promote organically produced cowpea crop. On the other hand, identification of responsive cowpea cultivars to insecticidal treatments will certainly catalyze the commercialization of cowpea production enterprise by medium to large scale farmers. The pest problem in cowpea is complex and requires diversified efforts. Any single effort will be a slow and frustrating process (B.B. Singh, personal communication).
The general objective of this research is to assess the productivity of ten cowpea genotypes under varying spray regimes, locations, seasons, and cropping system in the moist savanna of southeastern Nigeria agro-ecology.
The specific objectives are to:
- determine the effects of insecticide treatment on cowpea insect pests infestation and growth and yield of cowpea genotypes;
- determine the effects of time of seeding on cowpea insect pests infestation and growth and yield of cowpea genotypes;
- determine the effects of cropping system on cowpea insect pests infestation and growth and yield of cowpea genotypes; and
- establish appropriate combination of insecticide treatment, time of seeding and cropping system on insect pests management and growth and yield of cowpea genotypes.
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