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The study was carried out during the second season planting of 2014 at University of Uyo Teaching and Research Farm, Use-Offot, to evaluate the effect of planting dates on insect pest infestation of cowpea in Uyo, Akwa Ibom State. The experiment was laid out in a randomized complete block design and replicated three times. A medium maturing cowpea variety “Ife brown” was used as the planting material sown at four planting dates (15th September, 25th September, 5th October and 15th October).  Data was collected on incidence and severity count from black bean aphids (Aphis fabae),mung moth or legume pod borer (Maruca testulalis), pea pod borer (Etiella zinkenella), spiny brown bug (Clavigralla tomentosicollis) and also from the yield and yield components. Significant differences (P < 0.05) in the severity count and yield components were detected for each planting date. Higher seed yields were recorded from seeds sown in September 15 and 25 with mean values of 1.42t/ha and 1.31t/ha respectively while seeds sown in the latter month (October 5 and 15) produced lower yields comparatively, 0.90 and 0.41t/ha. Also, significantly higher incidence of Black bean aphids (Aphis fabae), Mung moth or Legume pod borer (Maruca testulalis), Pea pod borer (Etiella zinkenella) and Spiny brown bug (Clavigralla tomentosicollis) were observed for the seeds sown in October. Higher pest incidence and severity resulted in the lower yield of cowpea seeds grown in October.  Thus, from the study, cowpea (Vigna unguiculata  (L.)Walp.)can be grown with potential high yield returns with low insect pest infestation in September in Uyo, Akwa Ibom State.


1.0                            INTRODUCTION

1.1 Background of the Study

Cowpea (Vigna unguiculata (L.) Walp. ) is an important grain legume in the tropics and subtropics. It is a native to central Africa and belongs to the Fabaceae  family, and is eaten in the form of grain, green pods, and leaves (Adejumo, 2012). The roots are eaten in Sudan and Ethiopia, and the peduncles and stems are used as fibres in Nigeria. Cowpea is known as vegetable meat due to high amount of protein in the grain with better biological value on dry weight basis. The grain contains 26.61 % protein, 3.99 % lipid, 56.24 % carbohydrates, 8.60 % moisture, 3.84 % ash, 1.38% crude fibre, 1.51% gross energy, and 54.85% nitrogen free extract (Owolabi et al, 2012). It is mostly grown as an intercrop with sorghum, maize and millet (Asiwe, 2006). Cowpea is usually preferred by farmers because of its role in increasing soil fertility through nitrogen- fixation (Blade et al, 1997 and Asiwe, 2006) and production of nutritious livestock. Under sole cropping, the potential grain yield is high (1.5 - 3.0 tha-1), especially, when insecticide was applied. However, the actual yields
obtained by farmers in South Africa are much lower averaging less than 500 kg ha-1 (Asiwe, 2006 and Asiwe, 2009). Insect pests are considered to be largely responsible for this, as their attack can result in 90 - 100% yield reduction (Jackai and Daoust, 1986).

Cowpea is an annual herb with varying growth forms. It may be erect, trailing, climbing or bushy, usually indeterminate under favourable conditions. It has a strong taproot and many spreading lateral roots in surface soil. The first pair of leaves is basic and opposite while the rest are arranged in alternate patterns and are trifoliate. The leaves are usually dark green in colour. Leaves exhibit considerable variation in size (6 to 16 x 4 to 11 cm) and shape (linear lanceolate to ovate). The leaf petiole is 5 to 25 cm long. Stems are striate, smooth or slightly hairy with some purple shades. Flowers are arranged in racemose or intermediate inflorescences at the distal ends of 5 to 60 cm long peduncles. Flowers are borne in alternate pairs, with usually only two to a few flowers per inflorescence. Flowers are conspicuous, self-pollinating, borne on short pedicels and the corollas may be white, dirty yellow, pink, pale blue or purple in colour. Seeds vary considerably in size, shape and colour. Usually the number of seeds per pod may vary from 8 to 20. The seeds are relatively large (2 to 12 mm long) and weigh 5 to 30 g/100 seeds. The testa may be smooth or wrinkled; white, green, buff, red, brown, black, speckled, blotched, eyed (hilum white, surrounded by a dark ring) or mottled in colour. Fruit: pods that vary in size, shape, colour and texture. They may be erect, crescent-shaped or coiled. Usually yellow when ripe, but may also be brown or purple in colour (Production Guidelines for Cowpea, 2011).

Cowpea is mainly grown in tropical and subtropical regions in the world for vegetable and grain and to lesser extent as a fodder crop. It is a most versatile pulse crop because of its smothering nature, drought tolerant characters, soil restoring properties and multipurpose uses. More than 11 million hectares are harvested worldwide, 97% of which is in Africa. Nigeria cultivates 4.5million hectares annually representing over 60% of total production. The crop can be harvested in three stages; while the pods are young and green, mature and green and dry. The grain yield of cowpea in Nigeria is 700kg/ ha (FAO STAT, 2011). The highest production of cowpea comes from the northern states of Nigeria (about 1.7 million tonnes from 4 million hectares). The sale of cowpea seeds and fodder earns income to farmers. In Nigeria, farmers who cut and store cowpea fodder for sale at the peak of the dry season have been found to obtain as much as 25% of their annual income by this means. Cowpea also plays an important role in providing soil nitrogen to cereal crops (such as maize, millet and sorghum) grown after cowpea cropping (FAO STAT, 2011).

1.2 Origin and distribution of cowpea

Cowpea (Vigna  unguiculata (L) Walp) is a tropical, annual herbaceous legume, which belongs to the family Papilionaceae (Fabaceae), order Leguminosae and genus Vigna (Singh et al, 1997). The genus Vigna consists of over one hundred different species widely found in the tropical and sub-tropical regions, and has great morphological and ecological diversity (Ng and Monti, 1990 and Piano et al, 1990). The common names of this crop include black eye bean, southern pea, bean, cowpea, china pea and  cow grain. In Nigeria, it is commonly referred to as beans, “ewa” (Yoruba), “wake” (Hausa), “ikedi” (Igbo) and “okoti” (Ibibio). The crop can be grown on many soil types, but does best on well-drained, fertile, sandy-loam soils. Cowpea production is considered suitable in areas with annual rainfall of 750-1500 mm (Anthiono, 1979). Cowpea varieties could be prostate, semi-erect, erect or climbing. Pods could be coiled, round, crescent or linear (Rachie and Singh, 1985 ). Most cowpea cultivars are indeterminate in nature, producing flowers and seed over a long period. However, some are determinate and produce flowers and seed within a season of cowpea has been very difficult to determine, due to the fact that various researchers have reported different areas as centres of origin (Fatokun, 2002). Rawal, (1975) postulated that, based on the presence of wild progenitors of cowpea in West and Central Africa, the region was the centre of domestication of cowpea. This view was corroborated by Steele  (1965)who also reported that cowpea originated from sub-humid and semi-arid regions of West Africa. This view was also shared and supported by Steele, (1965). However, some studies on the genetic exploration of cowpea in Africa suggested that Swaziland may be the primary centre of origin of wild progenitors, because this country has higher species diversity throughout the world (Ng and Monti, 1990 and Mongo, 1996). Regardless of its centre of origin, cowpea is extensively cultivated in Africa, Asia, Australia, Brazil, the Caribbean’s, India and the United States of America (U.S.A). The major areas of production in Central and West Africa, which account for about 89 % of the total area of world production, are Nigeria, Niger, Mali, Burkina Faso, Senegal, Cameroon and Democratic Republic of Congo (FAO STAT, 2008). Modest amounts also emanate from Mozambique, Tanzania, Uganda, Sudan, Kenya and Somalia. Other producers are Myanmar, Haiti, Serbia, Sri Lanka and Egypt. The main producing areas in Nigeria are within the Guinea and Sudan savannahs (Mongo, 1996). However, some appreciable quantities are grown in the rain forest belts, particularly in the South West, which has two (2) growing seasons, namely; early (March – July ) and late (August – November) (Ebong, 1965). The major producing states in Nigeria include; Kaduna, Katsina, Zamfara, Bauchi, Sokoto, Kebbi, Plateau, Borno, Yobe, Jigawa, Niger, Benue, Nasarrawa and Kano where most cowpeas are traditionally grown as intercrops with cereals such as millet, maize and sorghum (Steele, 1965; Emechebe and McDonald, 1979 and Chemeda, 1997). In this system, the yields are low; inter-specific competition is high, population density is undetermined and harvesting is complicated by differing maturities of the intercrops (Singh  et al, 1997)  estimated a world total area of about 12.5 million hectares grown to cowpea annually. The food and Agricultural Organization of United Nations (FAO) estimated a production of more than 5.2 million metric tonnes of dry cowpea grains worldwide in the year 2010 (FAO STAT,2011). The report also showed that cowpea production in Nigeria accounted for 58 % of the total world’s output; making Nigeria the largest producer with an output of  2.9 million metric tonnes. Production in Nigeria is highest in the North East (703.13 metric tonnes from 641.03 ha), followed by the North West (519.51 metric tonnes from 1068.02 ha) and North Central (166.58 metric tonnes from 307.70 ha) (NAERLS and NFRA, 2009).

Despite cowpea importance in our diet and economy, it’s production has not met national demand due to low yield. According to FAO, 2013; in 2012, the average cowpea yield in West Africa was estimated to be 483kg/ha which is still 50% below the estimate potential production yield (Kormawa et al, 2002).

1.3 Economic importance and uses of cowpea

Cowpea (Vigna  unguiculata (L) Walp) is an important grain legume in the diet of many people in the third world countries as it provides not only high quality protein (25.4%) but also constitute the cheapest source of dietary protein for low income sectors of the population (Rachie and Singh, 1985). It is also a good source of carbohydrate (56.8%) calcium, iron, vitamin B and carotene. Although cultivated primarily for its edible seeds, direct consumption of cowpea leaves is also widespread in Africa (Rachie, 1985). In fresh form, the young leaves, immature pods and peas are used as vegetables, while snacks and main meal dishes are prepared from the dried grain (Nelson et al, 1997). Beside its usefulness in human diet, it serves as an important fodder crop in different parts of Africa (Quin, 1997). The haulm containing about 20% protein is highly valued feed and is sold for almost the same price as cowpea grain on dry weight basis (IITA, 1997). Thus, cowpea promotes crop livestock integration, thereby leading to a better nutrient cycling and enhanced income generation (Alghali, 1993). Although cowpea has high grain yield potentials ranging from 1.5 to 3.0 t/ha, actual yields in the traditional cropping systems in Africa are consistently low as the range is between 50 to 350kg/ha (Montimore et al, 2006 and Emechebe and Singh, 1997).

The cowpea is used both as a vegetable and grain. The semi spreading types are suitable for use as a vegetable. The use of cowpea seeds as a seed vegetable provides an inexpensive source of protein in the diet. The dried pulse may be cooked together with other vegetables to make a thick soup, or ground into a meal or paste, before preparation in a variety of ways. Similarly, fresh, immature pods may be boiled as a vegetable. Fresh leaves and growth points are often picked and eaten in the same way as spinach. Dried leaves are preserved and eaten as a meat substitute. Cowpea is also grown as a dual-purpose crop - the green pods are used as a vegetable and the remaining parts as livestock fodder. It is very palatable, highly nutritious and relatively free of metabolites or other toxins.

In West Africa where cowpea is very popular and a staple food, utilisation in family menus has advanced. For instance, in Ghana it is used to fortify cassava, plantain, cereal-based meals and yoghurt. In Nigeria, cowpea paste can be boiled or fried to produce a popular meal known as “moi-moi” that is served with rice during ceremonies, and “akara” served for breakfast. In South Africa, with advanced food technology compared to West African countries, cowpea utilisation is poor because production is still in the hands of smallholder farmers. It is envisaged that cowpea meals can be served with various popular maize meals, custard, bread, pap and rice in South Africa when production is increased and utilisation awareness improves. In many localities in Limpopo and Mpumalanga provinces cowpea leaves are harvested fresh as a vegetable for soup preparation or cured for future use during winter when there is no rain to sustain the crop production. The trading of seeds and processed foods provide both urban and rural opportunities for earning regular income. The aboveground plant parts of cowpea, except the pods, are utilised as animal fodder. Local farmers who cut and store cowpea fodder for subsequent sales at the peak of the dry season have been found to obtain as much as 25 % of their annual income in this way. It is mostly grown by the subsistence farmers in West and central sub-Saharan Africa where it’s grains and  stover are highly valued for food and forages for humans and animals (Adebiran  et al,  2012). Cowpea serves as soil cover due to its creeping nature, thus enhancing its effectiveness in soil conservation practices (Bationo et al, 2002). It also has the inherent ability to fix atmospheric nitrogen in soils through the bacteria in its root nodules which helps it grow well in poor soils (Singh, et al 2003). In addition, some cowpea varieties cause suicidal germination of the seed of Striga hermonthica, a parasitic plant that usually infests cereals with devastating effects (Quin, 1997).

Cowpea provides a rich source of proteins and calories as well as minerals and vitamins (Rangel, 2003). Nigeria and Niger accounts for 66% of world cowpea production (FAO, 2013).

Some major reasons for low yield of cowpea were attributed to inadequate access to improved varieties, pests and diseases (Emechebe, 2002), time of planting and inability to select cultivars adaptable to their ecological zone (Ikeh et al, 2013 and Abdullahi et al, 2012). Insect pests are a major factor in the low yields of cowpea in Africa and they affect each tissue component and developmental stage of the plant. In bad infestations, insect pressure is responsible for over 90% loss in yield (Jackai et al, 1986).

1.4               Justification of the Study

Despite cowpea’s importance and high yield potential in the Nigerian savannahs, insect pest attack is a major constraint upon production (Singh et al. 1990). Severity can vary, and sometimes lead to total yield loss (Singh and Allen, 1980). Yield losses of up to 70%, from insect pests alone, have been reported (Rusoke and Rubaihayo, 1994). In some areas, the losses caused by insect pests account for a reduction in grain yield as much as 80% (ICIPE, 1980). Cowpea growers in Borno State are at risk of losing the entire crop to insect pests in most growing seasons. The most damaging of all insect pests are those that attack the crop during the flowering and podding stages (Jackai et al. 1985). Worldwide, insect pests, especially Aphis craccivora Koch, Megalurothrips sjostedtiTrybom, Maruca virata Fab., and a complex of pod-feeding bugs cause the greatest yield reductions (Alghali 1992  and Omongo et al. 1997). In a recent study, Kamara et al. (2007) reported that flower thrips, the legume pod borer (Maruca) and a range of pod-feeding bugs were the major insect pests of cowpea in the dry savannahs of Northeast Nigeria. Maruca larvae damage flower buds, flowers, green pods, and seeds (Singh and Jackai 1985). Thrips start to attack at flower initiation, causing flower bud abortion (Akingbohungbe,1982). Adults and nymphs of pod bugs remove sap from green pods, causing abnormal pod and seed formation (Singh and Jackai 1985).

In the tropics and sub-tropics where most of the farmers are small holders with little or no access to chemical control measures or resistant varieties, control measures such as planting dates can be particularly important especially to the low input farming system (Bock and Jeger, 1999). Researchers have reported that improved cultivars and alteration of planting dates are effective strategies for reducing pest damage (Ekesi, et al and Karungi, et al., 2000). Accurate timing of sowing a crop in any particular location is an important agronomic requirement.

According to Akande et al, (2011), the traditional period of planting cowpea in this environment is between August and September but changes in climatic patterns have causes dramatic changes in cropping seasons and the effect of this changes have resulted in wide fluctuations in yield and seed quality of cowpea

Considering the economic importance of cowpea, there is need to evaluate effect of planting dates on pest incidence and severity as well as yield and yield components.

1.5 Objectives of the Study

Therefore, this study was carried out to assess level of insect pest infestation of cowpea in Uyo with the following objectives:

1)      To assess the effect of planting dates on incidence and severity of field pests of cowpea.

2)      To assess the effect of planting dates on growth and yield of cowpea.

3)      To make appropriate recommendation(s) based on the study findings.

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