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Spatial distribution and density of Striga hermonthica (Del.) benth infestation associated with cereal production in southern guinea savanna farming systems

Abstract This study describes the distribution patterns of S. hermonthica infestation present in 117 farmers’ fields located in 61 villages in the three major cereal growing areas of Benue and Nasarawa states. A total of 1098 respondents were randomly selected proportionate to the number of households in all the zones. Striga count was taken using a quadrat and farmers’ fields were visually assessed using a five-category ranking (very high density,high density, medium, low, very low density) and recording the geo referenced data. On average, 67.3 and 3.2% of the surveyed area were infested with high and low density of Striga, respectively. The mean number of Striga plants per m2 was greater at Nassarawa State (one to eighteen plants m-2) than Benue State (one to twelve plants m -2). In Benue, the largest percentage of Striga infestation was recorded in Buruku (49.7%) and the lowest was obtained in Guma (38.3%). In Nassarawa, under sorghum cultivation, higher Strigadensties were recorded in Karu and Awe LGA; while Doma, Keana and Obi LGA recorded moderate Striga infestation. In both locations, Striga infestation was highest in sorghum fields; while millet fields recorded the least. About 40% and 35.4% of the farmers reported that new modern farming methods and Striga control copping strategies, respectively are received from Extension agents , during Monthly Technology Review Meeting (MTRM). The study has provided baseline information on the spread of S. hermonthica in the Southern Guinea Savanna of Nigeria and therefore, copping strategies for its control should be intensified.

J. Bio. & Env. Sci. 2014

J. Bio. & Env. Sci. 2014 Introduction Witch-weed (Striga hermonthica, Orobanceaceae) is among the most economically and ecologically important parasitic flowering plants in sub-Saharan Africa. They are common and abundant parasites of the Poaceae and affect nearly all of the commercially important cereal species in the Nigerian savanna agro-ecological zones. Thegeographic regions with the greatest diversity and concentration of Striga are Northern Sahel and Sudan savanna, in the north eastern States with three taxa (including S. hermonthica, S. gesneriodies and Alectravogelii (Dugjeet al., 2006). Among which S. hermonthica is the most endemic spanning Southern Guinea Savanna agro-ecological zone with significant increased toward the Northern-most part of the country. The parasite infects cereal crops such as sorghum (Sorghum bicolor [L.]), pearl millet (Pennisetumglaucum[L.]), maize (Zea mays [L.] and upland rice (O. sativa [L.]), on which the populace largely depend for food in > 25 countries in Africa (Parker, 2009). The yield loss is often significant, ranging from 0 to 100 percent even under good management practices (Lagokeet al., 1991). These losses largely depend on the level of infection, crop variety, soil fertility and rainfall patterns (Menkir and Kling, 2007). The greatest impact of the parasite is on infertile soils, and the most affected are the poor subsistence farmers (Kabambeet al., 2008). The parasite is highly prolific and is capable of producing 10,000 – 200,000 tiny seeds per mature plant than can survive in the soil for > 10 years (Hearne, 2009). It harms and caused a physiological damage to the host plant under the ground even before emergence (Gurney et al., 2006). The parasite’s abundance seed production, longevity in the soil and subterranean attack to the host plant coupled with the activities of humans have increased the scale and severity of infections. Demographic pressure due to the increased in human population have exacerbated intensive land use, depletion in soil fertility and changes in cropping systems. Albeit this underlying causes has hitherto led to inability of the peasant farmers to afford the cost of fertilizer to replenish the soils, increased pastoralism and intensification of cereal-based mono-cropping, thus increasing the ability of Striga to strive due to host presence and movement of seeds from place to place. Several promising Striga containment strategies have been developed, ranging from those that relate to soil fertility improvement to those that directly affect the parasite (Rector, 2009). This has given the farmers with a variety of options to control the parasite, including the use of chemical herbicides, trap cropping, hand pulling, appropriate fertilizer applications, crop rotation, intercropping, resistant crops, and biological control (Parker and Riches, 1993; Menkir and Kling, 2007; Hearne, 2009). However, the knowledge of the spread and spatial patterns of Striga diversity are fundamental for both ecological and biogeographical analyses and for priority setting approaches in nature conservation. During the last decade, several research programmes were started to map and analyse the spatial patterns of Striga endemism on Nigerian savanna (Lagokeet al., 1997). However, most of these approaches regarded only Sahel and Northern Guinea Savanna or "hotspot" areas without giving information for other areas in the Southern Guinea Savanna especially in Benue and Nasarawa states. Information on the distribution and hosts of Striga in Benue state has been primarily based on the work of (Suleet al., 2008). Suleet al., (2008) provided distribution of Striga found in Benue state, primarily based on their collections obtained from 2004–2006 and no information for Nasarawa state. More recent collections, however, will provide additional information on Striga distributions and hosts in the region. In Nasarawa, as in remaining Benue north, recent observations have shown that habitat affiliation seems to change and that distribution of S. hermonthica has recently increased (Ibrahim, A., personal observation).Hence, it may be argued that further spread may create severe agricultural problems in the areas. Analysing the spatio-temporal patterns of spread may help to identify underlying mechanisms, provide 420 | Ibrahim et al.

J. Bio. & Env. Sci. 2014 evidence for assessing the potential of further expansion and identifying management strategies. Therefore, the main objectives of this study were (1) to provide a detailed description of the spatial distribution patterns of S. hermonthica in crop fields located in major cereal producing areas of Benue and Nasarawa states, (2) to identify associations between presence of S. hermonthica and management variables in the farming systems of the Southern Guinea savanna. Materials and methods The field study was conducted between August and November of 2010 in the zone B of the Benue State Agricultural and Rural Development Agency (BNARDA) and the three zones of the Nasarawa State Agricultural Project (NADP) of Nasarawa state in the Southern Guinea Savanna of Nigeria between 07 o .27’ - 08 o .25’ N and 07 o .17’- 09 o .19’E. The BNARDA zone B is made up of seven Local Government Areas (LGAs) – Buruku, Gboko, Guma, Gwer, Gwer-West, Makurdi and Tarka. The NADP zones comprised of thirteen LGAs including Northern zone: Karu, Keffi, Kokona, Nasarawa and Toto; Central zone: Akwanga, Nassarawa - Eggon and Wamba and Southern zone: Awe, Doma, Keana, Lafia and Obi LGA. A total of 18 sites across the 7 LGAs (BNARDA) administrative areas within zone B) in Benue state and 43 sites across the three zones (NADP administrative areas) in Nasarawa state were surveyed (Tables 1and 2). A total of 1098 respondents were randomly selected proportionate to the number of households in all the zones. The choice of wards and households interviewed was done using a table of random numbers, while the respondents selected and interviewed was made based on work load for the Village Extension Agent (VEA) and the number of VEAs in the ecological zone. Table 1. Coordinate locations and altitudes of S. hermonthica surveyed area in Benue State used in the study. State L.G.A Village Longitude (E) Latitude (N) Altitude (m) Benue Buruku Agwabi 009.19 o 07.46 o 129 ± 3.96 Benue Gboko Abwa 009.13 o 07.32 o 163 ± 3.42 Benue Gboko Mkar 009.08 o 07.35 o 219 ± 3.13 Benue Gboko Yandev-Mbator 009.04 o 07.38 o 199 ± 3.05 Benue Guma Agasha 008.80 o 07.73 o 89 ± 3.66 Benue Guma Uikpiam 008.64 o 07.97 o 181 ± 4.27 Benue Gwer Aliade 008.49 o 07.30 o 179 ± 4.27 Benue Gwer Ikpayongu 008.60 o 07.54 o 198 ± 3.66 Benue Gwer Mase 008.52 o 07.33 o 203 ± 4.27 Benue Gwer Taraku 008.27 o 07.27 o 105 ± 3.66 Benue Gwer – West Naka 008.18 o 07.34 o 103 ± 3.05 Benue Makurdi Adaka 008.46 o 07.30 o 88 ± 4.27 Benue Makurdi Agan 008.34 o 07.81 o 155 ± 3.66 Benue Makurdi Apir 008.56 o 07.62 o 146 ± 4.27 Benue Makurdi Daudu 008.56 o 07.91 o 127 ± 4.27 Benue Tarka Asukunya 008.87 o 07.65 o 165 ± 3.35 Benue Tarka Terhimbe 008.93 o 07.49 o 197 ± 4.27 Benue Tarka Wannune 008.88 o 07.59 o 197 ± 3.66 Questionnaires were administered by the Village Extension Agents to back up personal interviews. Coordination of the questionnaires was by Agricultural Extension Officers (AEOs) who were monitored by the respective Zonal Extension Officers (ZEOs).An orientation on the administration of the questionnaires by the VEAs was done at the Monthly Technology Review Meeting (MTRM) meeting prior to the commencement of the survey to ensure efficiency. The survey was conducted through farm visits and standard questionnaire developed by the Pan - Africa Striga Control Network (PASCON). The entire questionnaire addresses farmers’ Striga perception, household and demographic characteristics of the respondents, copping strategies, cropping history, varieties grown, the impact of 421 | Ibrahim et al.

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