Department of Crop Science
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Item Identification of Maize Leaf Diseases Based On AlexNet and ResNet50 Convolutional Neural Networks(2023-08-30) Micheni, Maurice; Birithia, Rael; Mugambi, Cyrus; Too, Boaz; Kinyua, Margaret KMaize crop protection is crucial for global food security, requiring accurate disease identification. In Kenya, farmers rely on subjective visual analysis of symptomatic leaves, which is time-consuming and prone to errors. Computer vision technologies, like deep learning and machine learning, offer promising solutions for disease identification. This study applies Convolutional Neural Networks (CNNs), specifically AlexNet and ResNet-50, to automatically learn image features and enhance speed and accuracy in maize leaf disease identification. A dataset of 3200 digital maize leaf disease images from Embu County is used for training and testing. AlexNet achieved the highest average accuracy of 98.3%, followed by ResNet-50 at 96.6%. The machine learning, support vector machine (SVM) exhibited the lowest average accuracy of 85.5%. These findings highlight the significance of utilizing AlexNet and ResNet-50 in maize leaf disease identification and classification.Item Effect of Intercropping on Potato Bacterial Wilt Disease and Tuber Yield in Kenya(Karatina University, 2023-12-06) MUSAH, S.M.; Birithia, R.K.; Kamiri, H.W.; Kahariri, E.Potato (Solanum tuberosum L.) is a major tuber crop in Kenya, whose productivity is heavily impaired by bacterial wilt disease, caused by Ralstonia solanacearum (Smith). Existing management strategies have not been effective, owing to the diversity and robustness of the pathogen and variation in the host range. The objective of this study was to evaluate the effectiveness of intercropping on the incidence of bacterial wilt and yield of potato in Kenya. A field experiment was conducted in four potato-growing counties, namely; Nyandarua, Nakuru, Bomet and Bungoma in Kenya. Treatments included intercroping with spring onion (Allium fistulosum L.); garden pea (Pisum sativum L.); and cabbage (Brassica oleracea var. capitata L.). Treatments also included a pure stand of potato as the control. Generally, intercropping had a significant suppressive effect (P<0.05) on the incidence and severity of bacterial wilt disease. Intercropping potato with spring onion, in particular, had the highest disease suppressive effect, followed by intercropping potato with cabbage; and lastly by potato with garden pea. Accordingly, potato-onion intercrop recorded the highest potato tuber yield (12.9 t ha-1), while the potato pure stand recorded the lowest tuber yield (7.9 t ha-1). Bacterial wilt disease incidence positively correlated with disease severity (r = 0.931; P<0.05). In contrast, the disease incidence and severity negatively correlated with tuber yield. In terms of Land Equivalent Ratio (LER), the highest value (1.64) was with potato-onion intercrop; and the lowest (1.35) with the potato-garden pea intercrop.Item The Role of Farmer Field Schools Approach in Improving Tea Production among Smallholding in Kenya.(2015) Chimoita, Evans L.; Maina, Gatahi Dennis; Olila, Dennis Opiyo; Onyango, Joseph P.GweyiTea production, processing and marketing in Kenya is under management of two sectors. The two sectors include; Kenya Tea Development Agency which manages approximately six hundred thousand small scale farmers and multi-nationals sector for example Uniliver/Lipton teas, James Finlay’s and George Williamson holdings manage privately plantations and estates of tea. The volume and frequency of plucking tea leaves enhances net revenue for small scale tea farmers in Kenya. The main objective was to determine the role of Farmer Field Schools extension approach and eventual outcome tea production among small scale farmers in Kenya. The study assessed the trends and the influence of Farmer Field Schools (FFS) approach in addressing productivity of tea leaves. The study employed descriptive statistics and mean trends analysis to determine the influence of FFS in tea production. The study sites were six sub locations of tea growing areas. The sites were purposively since they were pilot areas where the initial farmer field schools were collaboratively initiated by Kenya Tea Development Agency (KTDA) and Uniliver/Lipton teas for enhancement of tea production. The study gathered primary data from sampled tea farmers by use of structured questionnaires. Secondary data was sourced from the KTDA archives records. Research findings revealed a positive trend in green tea leaf production and as well as revenue. Further, it was revealed that social positive effects such as farmers willingness to participate in group activities and sustainable tea husbandry, promotion of self-mobilization and interactive participation enhanced tea production. The positive economic-agricultural productivity effects were; the transfer and adoption of agricultural technologies particularly in tea growing that enhanced revenue, increased access to knowledge and agricultural information.Item Enhancement of bacterial wilt resistance and rhizosphere health in tomato using bionanocomposites(Springer, 2016-12) Gatahi, Dennis; Wanyika, Harrison Njuma; Kavoo, Agnes Mumo; Kihurani, Agnes WanjiruBiological control agents are useful components in the enhancement of plant disease resistance and improvement of soil properties. Effect of biological control agents (BCAs) as a disease control method in plants is hampered by their vulnerability to environmental and edaphic conditions. This study entailed the use of chitosan-silica nanocomposites for delivery of BCAs. Effect of BCAs-nanocomposite complexes (bionanocomposites) on resistance of tomato plants to bacterial wilt, mycorrhizal root colonization and rhizosphere soil properties were investigated. Replacement of mesoporous silica nanoparticles (MSN) in the nanocomposite with nano synthesized clay was also assessed on disease resistance. Tomato seeds and seedlings were pre-treated using bionanocomposites and then inoculated by Ralstonia solanacearum isolated from infected tomato plants in a greenhouse. Bionanocomposites treatment of tomato plants caused a significant increase (P≤0.05) in the level of pathogenesis-related biochemicals such as chitinase and glucanase. Furthermore, beneficial microbial colonization was significantly (P≤0.05) induced in roots treated with the bionanocomposites. Wilting incidence and symptoms were reduced by over 50% when bionanocomposites were used. There was no significant effect (P≤0.05) on induced host plant resistance when mesoporous silica nanoparticles (MSN) were substituted with nanoclay particles. Therefore, due to ease of availability with no significant (P≤0.05) difference in efficacy between the nanoparticles, replacement of MSN with nanoclay in synthesis of the bionanocomposites is recommended. We argue that substitution of nanoclay with MSN makes the process of synthesizing the bionanocomposites sustainable.Item Control of Bacterial Wilt in Tomato Using Chitosan Intercalated with Tea Extracts.(OJS/PKP, 2022-04-21) Gatahi, Dennis; Kihurani, Agnes; Harrison, WanyikaIn this study, tea extracts were intercalated in chitosan gel to enhance the inhibitory effect of the complex on bacterial wilt in tomato. The disease caused by Ralstonia solanacearum can result in 100% crop loss under severe infection. Chitin was ground into powder of 0.1 mm size, deacetylated using concentrated NaOH solution and tea extracts from green, purple and black tea adsorbed through rotary evaporation. Confirmatory tests on effective adsorption were done using FTIR and XRD, while bioassay experiments were performed to determine efficacy of the chitosan intercalated with crude tea extracts (CICTE) on the pathogen and tomato growth. In vitro and In situ tests were carried out in growth chambers and greenhouse respectively. The greenhouse trials were conducted for a period of 2 years in three sites i.e. Gatundu, JKUAT and Makuyu. The bioassays demonstrated significant (p < 0.05) reduction of R. solanacearum turbidity marked by change of optical densities (OD) from 3.55 to 1.04. In addition, there was significant (p < 0.05) inhibition of the cultured R. solanacearum and reduced wilt incidence in tomato plants treated with CICTE and later inoculated with the pathogen. Tomato plants treated with CICTE also recorded a significantly (p < 0.05) higher yield compared to the control. The study therefore recommends utilization of CICTE as an effective and environmentally safe biopesticide for the devastating bacterial wilt pathogen.Item Management Strategies of Prosopis juliflora in Eastern Africa: What Works Where?(2024-04-22) Kamiri, Hellen Wangechi 1,2, *; Choge, Simon K. 3; Becker, Mathias 2Abstract: Prosopis juliflora is a shrub/tree originating from the Americas. Since its introduction for fuel wood afforestation into eastern Africa, it has been invading crop- and rangelands with negative effects on the environment and on livelihoods. Understanding the management strategies for Prosopis and matching them with ecological, social-cultural, and economic needs of the eastern African region is a pressing scientific issue. We analyzed management strategies of Prosopis, focusing on determinants and drivers of their choice of applied management strategies as well as their effectiveness. We identified 1917 scientific contributions published between 1970 and 2022. Following a multi-step screening, we reduced the references to 53 relevant (internationally) published papers with a focus on the management of Prosopis in the east African region. Analysis of the literature shows that factors driving invasion dynamics but also land users’ social-economic as well as cultural attributes determine the type of management strategy and shape local control actions. Main strategies comprise (1) physical containment of invasive spread, (2) chemical, mechanical and biological approaches to reduce stand densities, (3) complete eradication, (4) restoration of invaded land, and (5) economic use of Prosopis products. Adopted strategies are based on actual and perceived impacts of invasion, and the adoption and success of individual strategies is highly location specific.Item Seasonality and potential of Ceranisus menes for control of thrips on French beans(Sida, 2008-10-22)-Item Home Sustainable Management of Invasive Pests in Africa Chapter Influence of Predatory Mites, Phytoseiulus longipes Evans. on the Within-Plant Diurnal Migration and Distribution of the Red Spider Mite, Tetranychus evansi, Baker and Pritchard on African Nightshade, Solanum scabrum(Springer, 2020-07-14) Kungu, Miriam; Subramanian, Sevgan; Salifu, Daisy; Fiaboe, Komi K. M.; Azandémè-Hounmalon, Ginette Y.; Gitonga, Linus; Onyambu, Gladys K.; Deletre, Emilie; Martin, ThibaudUnderstanding the within-plant diurnal migration and distribution of the Red spider mite, Tetranychus evansi Baker and Pritchard, in the presence of the predatory mite Phytoseiulus longipes Evans, on African nightshade, S. scabrum, is critical in developing an Integrated Pest Management (IPM) strategy for the pest. The T. evansi density, day and night cycles, and presence of P. longipes, on the within-plant migration and distribution of T. evansi on African nightshade were hence investigated. The results indicated that T. evansi does not exhibit a circadian migratory movement pattern on S. scabrum at lower densities (50 and 100 mites). However, T. evansi was observed to have a density-dependent collective displacement and distribution to the top of the plant, as densities increased (300 and 600 mites). The presence of P. longipes on the plant enhanced the within-plant migration of T. evansi, even at low densities (50 and 100 mites). However, there was no apparent pattern of migration and movement that was observed within the plant. The increased within-plant movement of T. evansi in presence of the predatory mites and collective displacement of T. evansi at higher densities indicate a potential for developing an IPM strategy using the acaricide treated net, which is discussed further.Item Evaluation of biological attributes of a native egg parasitoid, Trichogrammatoidea sp. nr. lutea (girault), kenyan accessions(2012-09-10) Lagat, Zipporah Osiemo; Gitonga, Linus; Muya, Shadrack Muvui; Ng ' Endo, RossaObjective: This study was carried out to evaluate the biological attributes that is, parasitism, adult progeny production, and sex ratio of 21 strains of a native egg parasitoid Trichogrammatoidea sp. nr. lutea Girault (Hymenoptera: Trichogrammatidae) collected from Plutella xylostella Linnaus (Lepidoptera: Yponomeutidae) in coastal Kenya, reared on Corcyra cephalonica Sainton (Lepidoptera: Pyralidae) in the laboratory. Methods:Atotal of 21 accessions of T.sp. nr. lutea were assembled from the Kenyan coast (Shimba hills and Muhaka sites). Preliminary experiments to select the best performers among the 21 strains, based on biological attributes such as adult longevity, parasitism, emergence, adult progeny produced and progeny sex ratio were conducted under laboratory conditions (temperature of 27±2°C and 65±10% RH). Results: There were significant differences (P<0.05) in all biological attributes studied among the strains. The overall mean adult longevity was 9.31 days. Parasitism, emergence and sex ratio per adult female were 20.2%, 75.56% and 37.77% respectively. The wasp age influenced all the attributes tested significantly (P<0.05) of T.sp. nr. lutea. Conclusion: Four accessions (SH-1 and 4, MK-1 and 3) were selected and recommended from this experiment based on adult longevity, parasitism, adult progeny produced and sex ratio for further evaluation. The results from this study will be useful for mass rearing purposes as well as for future field release programmesItem Biological control agents of aphids (Homoptera: Aphididae) on potatoes (Solanum tuberosumL) in Kenya(2010) Machangi, J. M.; Gitonga, L. M.; Nderitu, J. H.; Maniania, N. K.; Kabira, J. N.A field survey was conducted in four major potato growing areas in Kenya (Kiambu, Nyandarua, Meru and Molo Districts) during January and February, 2008 (short rains crop) and June 2008 (long rains crop) to determine the occurrence of predators, parasitoids and pathogens of the aphids Myzus persicae Sulzer and Aphis gossypii Glover in potato crops. In each of the four areas, 30 potato farms distributed in different parts of the survey area were selected at random for the surveys. Insects collected were brought to the laboratories at the International Centre of insect physiology and Ecology (icipe), Nairobi, for identification and fungal infection. For isolation of fungal pathogens, dead aphids were transferred on moist filter paper placed on sterile Petri dishes to allow the growth of the fungus on the surface of the cadaver, after which fungus was transferred on artificial media for isolation. Four aphid species, M. persicae, A. gossypii, Macrosiphum euphorbiae Thomas and Aulacorthum solani Kaltenbach were identified in all the four survey areas. Sixteen predator species of the aphids were identified. The most prevalent were the ladybeetles Harmonia axyridis (Pallas) and Hippodamnia convergens Guérin-Méneville (Coleoptera: Coccinellidae), followed by the minute pirate bugs, Orius spp. (Heteroptera: Anthocoridae) and the aphid eating gall midge Aphidoletes aphidimyza Rondani (Diptera: Cecidomyiidae). Three hymenopteran parasitoid species (Braconids followed by Chalcids then the Ichneumonids) and four fungal pathogen species, Beauveria bassiana Balsamo (Ascomycota: Hypocreales), followed by Verticillium lecanii Zimmermann (Hypocreales: Incertae sedis), Metarhizium anisopliae (Metsch.) Sorokin (Deuteromycotina: Hyphomycetes) then Pandora neoaphidis (Remaudière &Hennebert) Humber (Zygomycetes:Entomophthorales) were identified in all four areas of the field survey.