Spatial distribution and pest pressure on key crops in Nyeri county, Kenya using agro-ecological zone -based sampling
Paper Details
Spatial distribution and pest pressure on key crops in Nyeri county, Kenya using agro-ecological zone -based sampling
Abstract
This study examined the spatial distribution and ecological dynamics of insect pest pressure on major crops in Nyeri County, Kenya, using an agro-ecological zone (AEZ)–based framework. Research was conducted across six sub-counties—Mathira East, Mukurweini, Kieni East, Othaya, Tetu, and Nyeri Town—representing three AEZs: Upper Highland (UH2), Lower Highland (LH3), and Upper Midland (UM3. The objective was to generate spatially explicit insights into pest diversity, crop vulnerability, and farmer management practices to support targeted pest control interventions. A cross-sectional survey of 128 farms was carried out during the March–September 2025 cropping season using stratified random sampling. Data were collected through structured questionnaires, field observations, and GPS mapping to assess pest incidence, crop health, pest diversity, and farmer knowledge. Pest pressure was quantified by species richness and frequency per farm, while crop health was scored on a standardized 1–5 index. Statistical analyses included one-way ANOVA with Tukey’s HSD, multiple linear regression, and Pearson correlation. Ecological diversity was assessed using Shannon (H′), Simpson (D), and Pielou’s evenness (J′) indices, while crop vulnerability rankings incorporated pest counts, health indices, and variability measures. Results identified UH2 as a pest hotspot, exhibiting the highest pest diversity and lowest crop health. Pest abundance showed a strong negative relationship with crop health (p < 0.001), with Mathira East recording significantly higher pest pressure than other sub-counties. Cabbage, kales, and maize were the most susceptible crops, whereas tea, banana, and apple were relatively resilient. Although 83% of farmers relied on synthetic pesticides, limited dosage knowledge reduced effectiveness. Integrated Pest Management, though less widely adopted, was rated most effective (mean = 4.3). These findings underscore the need for AEZ-specific, education-driven pest management strategies to enhance sustainable crop production in Nyeri County
Bari R, Jones JD. 2009. Role of plant hormones in plant defense responses. Plant Molecular Biology 69, 473–488. https://doi.org/10.1007/s11103-008-9435-0
CABI. 2018. Pest management decision guides for smallholder farmers. CABI, Wallingford, UK.
CABI. 2023. Invasive pest outbreaks and crop losses in Sub-Saharan Africa. CABI, Wallingford, UK.
CEJAD. 2019. Pesticide use and pest pressure among smallholder farmers in Kenya. Centre for Environment Justice and Development, Nairobi, Kenya.
FAO. 2021. Integrated pest management: Guidelines for sustainable crop protection. Food and Agriculture Organization of the United Nations, Rome, Italy.
FAO. 2022. Fall armyworm and whitefly outbreaks in Africa: Impacts and responses. Food and Agriculture Organization of the United Nations, Rome, Italy.
FAO. 2023. Global crop losses due to pests and pathogens. Food and Agriculture Organization of the United Nations, Rome, Italy.
Flor H. 1971. Current status of the gene-for-gene concept. Annual Review of Phytopathology 9, 257–276. https://doi.org/10.1146/annurev.py.09.090171.001353
Gitonga ZM, Wabule MN, Mwangi JK. 2020. Pest diversity and horticultural intensification in Kenyan highlands. African Journal of Agricultural Research 15(4), 512–520. https://doi.org/10.5897/AJAR2020.14845
IPPC. 2022. Economic impact of invasive pests and global trade. International Plant Protection Convention, Rome, Italy.
Karanja J, Muthomi J, Kamau J. 2021. Ecological surveillance for pest detection in smallholder systems. International Journal of Pest Management 67(2), 145–153. https://doi.org/10.1080/09670874.2020.1787065
Kenya National Bureau of Statistics. 2024. Economic survey: Agriculture and rural employment. KNBS, Nairobi, Kenya.
Ministry of Agriculture. 2022. Migratory and invasive pests and weeds management strategy (2022–2027). Government of Kenya, Nairobi, Kenya.
Muriuki A, Ndegwa P, Wanjohi R. 2022. Spatial variation in pest pressure and land use in Nyeri County. Kenya Journal of Agricultural Sciences 18(1), 33–42.
Nderitu J, Wamae L, Gichimu B. 2017. Pest burden and crop performance in central Kenya. East African Agricultural and Forestry Journal 83(1), 21–29. https://doi.org/10.1080/00128325.2017.1313285
Okonjo W, Otieno D, Mugo S. 2018. Microclimatic drivers of pest incidence in Kenyan highlands. Journal of Environmental Studies 12(3), 88–96.
Plantwise. 2019. Pest-host interactions in East African cropping systems. Plantwise, Wallingford, UK.
Wainaina J, Mwangi P, Njuguna E. 2020. Crop susceptibility to insect pests in Kenya: A review. Journal of Crop Protection 9(2), 101–110.
M. Muriithi*, J. W. Wakagwa, P. G. Maina, D. Gatahi, A. Njeri , Maina Mwangi, 2026. Spatial distribution and pest pressure on key crops in Nyeri county, Kenya using agro-ecological zone -based sampling. Int. J. Agron. Agric. Res., 28(2), 1-11.
Copyright © 2026 by the Authors. This article is an open access article and distributed under the terms and conditions of the Creative Commons Attribution 4.0 (CC BY 4.0) license.