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Articles by J.H. Nderitu
Total Records ( 12 ) for J.H. Nderitu
  J.W. Kimenju , A.M. Kagundu , J.H. Nderitu , F. Mambala , G.K. Mutua and G.M. Kariuki
  Green manure plants were evaluated to determine their suitability as rotation crops with common bean to suppress root-knot (Meloidogyne spp.) nematodes. They were also evaluated as soil amendments in nematode control. The plants were Calliandra calothyrsus, Canavalia ensiformis, Chenopodium quinoa, Crotalaria juncea, Desmodium uncinatum, Gliricidia sepium, Leucaena leucocephala, Mucuna pruriens, Tephrosia purpurea, Tithonia diversifolia, Vicia villosa, Sesbania sesban and Tagetes minuta. In the glasshouse, pots were filled with steam-sterilized soil and sown with green manure plants. The rotation experiment entailed growing green manure plants for three months before uprooting them and planting beans in the same pots. The potting medium was infested with 6000 eggs/juveniles of Meloidogyne javanica. The field experiments were carried out in microplots infested with a mixture of M. javanica and M. incognita. Damage to bean roots due to root-knot nematodes was based on galling indices while nematode reproductive potential was based on egg mass index. Tithonia diversifolia, D. uncinatum, T. minuta, L. leucocephala and C. juncea were among the most effective in root-knot nematode suppression when used in rotation with beans. Their galling indices ranged between 1.0 and 1.5 under field conditions and were thus considered resistant. Vicia vilosa, T. purpurea and S. sesban were susceptible with galling indices ranging between 6.2 and 7.7. The resistant plants reduced the reproductive potential of Meloidogyne spp. by up to 80% while the susceptible plants caused an increase of up to 600%. Therefore, T. diversifolia, D. uncinartum, T. minuta, L. leucocephala and C. juncea can be recommended for use in fields infested with root-knot nematodes.
  J.W. Muthomi , J.N. Nyaga , F.M. Olubayo , J.H. Nderitu , J.N. Kabira , S.M. Kiretai , J.A. Aura and M. Wakahiu
  Field studies were carried out in farmer-based seed potato production to determine the incidence of potato aphids and potato aphid-transmitted viruses in two potato-producing areas of Kenya. Parameters determined included aphid population, virus disease incidence and tuber yield. Aphid population was monitored on leaves and in water-pan traps. Virus infection was determined based on symptoms and the viruses were identified in tubers sprouts by DAS-ELISA. Tuber yield was determined for plants showing virus symptoms and healthy-looking plants. Five aphid species were identified, with the most abundant being M. euphorbiae and A. gossypii on leaves and M. persicae and A. gossypii in water traps. The average aphid population was between 1.4 and 4.2 aphids per three leaves and 4.68 and 9.64 aphids per water pan trap. Farms with higher population of M. persicae had higher virus disease incidence. The most prevalent viruses were PVS, PLRV and PVM. Healthy looking plants had a latent infection rate 57.2% compared to 76.6% for symptomatic plants. Virus infection reduced the number and weight of tubers by 74 and 62.7%, respectively. However, virus infection increased the number and weight of the chats grade. The results indicated that aphid infestation and virus disease incidence were higher than the recommended for seed potato production. Therefore, there is need to create awareness among the farmers on aphid and virus symptom recognition and use of clean certified seed potato.
  P.E. Otieno , J.W. Muthomi , G.N. Chemining`wa and J.H. Nderitu
  Field experiments were conducted to investigate the response of grain legumes to rhizobia inoculation, farmyard manure and inorganic fertilizer nitrogen. The grain legumes were common bean (Phaseolus vulgaris L. var GLP 2), lima bean (Phaseolus lunatus L.), green gram (Vigna radiate L.) and lablab (Lablab purpureus L.). The experimental design was a randomized complete block design with split plot arrangement and replicated thrice. Parameters determined were the number of nodules and nodule dry weight per plant, seed yield and yield components. Nitrogen fertilizer application significantly reduced the number of nodules in most of the legume species. In contrast, rhizobia inoculation increased number of nodules and nodule dry matter in most species but this was not translated into increase in plant growth or grain yield. Application of manure improved nodulation and grain yield only in the short rains. However, fertilizer application significantly increased dry matter in both seasons and total grain yield during short rains. The study indicated that the effect of rhizobia inoculation, farmyard manure and nitrogen fertilizer on grain legumes is variable depending on species, parameter being measured and other environmental factors.
  J.W. Muthomi , P.E. Otieno , G.N. Chemining wa , J.H. Nderitu and J.M. Wagacha
  Greenhouse experiments were conducted over two cropping cycles to investigate the effect of fungicide seed treatment and fungal root rot pathogens on nodulation and dry matter accumulation of selected food legumes. The legumes were common bean (Phaseolus vulgaris L. variety GLP 2), green gram (Vigna radiata L. variety M66) and lablab (Lablab purpureus L.) while the pathogens were Fusarium oxysporum f. sp. phaseoli, Macrophomina phaseolina, Sclerotinia sclerotiorum and Rhizoctonia solani. Treatments consisted of inoculation of legume seeds with appropriate rhizobia alone, rhizobia together with fungicide, rhizobia together with pathogen and a combination of rhizobia, fungicide and pathogen. Fungicide copper oxychloride was used as a seed dresser. Rhizoctonia solani and S. sclerotiorum were more pathogenic and showed significantly increased seedling mortality and greater reduction in seedling emergence, number of nodules and root dry matter. Fungicide seed dressing significantly increased seedling emergence and reduced seedling mortality. However, fungicide seed dressing alone and in combination with pathogen depressed nodulation in all the legumes. Inoculation with F. oxysporum and M. phaseolina had no significant effect on nodulation in common bean. All the treatments had little or no significant effect on shoot dry matter. The results suggest that fungicide seed treatment in combination with rhizobia inoculation is beneficial in management of root rot and enhancement of nodulation in food legumes.
  R.D. Narla , J.W. Muthomi , S.M. Gachu , J.H. Nderitu and F.M. Olubayo
  Field experiments were conducted over two growing seasons to determine the effectiveness of vegetable intercrops in the management of downy mildew (Peronospora destrutor) and purple blotch (Alternaria porri) of bulb onion. Vegetable intercrops evaluated, were carrot (Daucus carota), spider plant (Cleome gynandra) and French bean (Phaseolus vulgaris). The efficacy of the vegetable intercrops in reducing the foliar diseases was compared to a fungicide Tata Master™ (metalaxyl8%+mancozeb 64%). Each vegetable was intercropped with three onion varieties (Bombay Red, Red creole and Orient F1) and downy mildew and purple blotch development were determined until physiological maturity. Vegetable and bulb yields were also determined at harvest. The vegetable intercrops significantly reduced downy mildew and purple blotch severity but had no significant effect on disease incidence. Spider plant was the most effective vegetable intercrop in reducing downy mildew severity by up to 21% and purple blotch severity by 18%. Onion varieties Red creole and Bombay red had low disease levels compared to orient F1. Although intercropping onion with vegetables reduced bulb yield, it improved the gross return per unit area. The results showed that intercropping bulb onion with vegetables could be beneficial in reducing foliar diseases and improving gross return per unit area. However, further studies are necessary to determine the optimal spatial arrangements of onion and vegetable intercrops in foliar disease management.
  J.H. Nderitu , E.M. Wambua , F. Olubayo , J.M. Kasina and C.N. Waturu
  A field study was conducted in 2002 to evaluate the combined effectiveness of insecticides and varietal resistance in the control of thrips infestation and damage at Kabete, Central Kenya. Four test varieties (Amy, Monel, Samantha and Impala) of French beans (Phaseolus vulgaris L.) and four insecticides (Lambda-cyhalothrin (Karate 1.75 EC), Petroleum spray oil (DC Tron 500 ML), Spinosad (Tracer 480 SC) and Fipronil (Regent 50 SC)) were used. The experiment was set in a split plot design, with variety forming the main plot and insecticide the subplot. Results show both varieties and insecticides influenced thrips infestation independently. For example, Tracer 480 SC and Regent 50 SC sprayed plots had the lowest thrips numbers across all varieties. Individual thrips species infestation differed across the treatments. For example, the mean number of Frankliniella occidentalis (Pergande) in Karate 1.75 EC sprayed plots was higher and significant compared to plots sprayed with Tracer 480 SC and Regent 50 SC but mean number of Megalurothrips sjostedti Trybom was not significantly different in all plots except those sprayed with DC Tron 500 ML and the control (unsprayed) plots. The research concludes by discussing the implications and applicability of the findings in French bean IPM systems in Kenya.
  J.H. Nderitu , M.J. Kasina , G.N. Nyamasyo , C.N. Waturu and J. Aura
  This study was conducted to measure economic benefit of using different spray schedules to control thrips on French beans. It was done using different spray regime scenarios of two insecticides: Lambda cyhalothrin (Karate 1.75% EC) and Methiocarb (Mesurol 500 SC). It is shown that increasing the number of sprays results to lower thrips infestations, explaining why local farmers practice calendar spraying. However, this lowers the net returns obtained from French bean sales. In contrast, application of one to two sprays maintains thrips below economic damage and provides the highest net returns. It is suggested that farmers should only use the effective insecticide after noting a density of three thrips per flower. This is possible if farmers embrace monitoring of thrips buildup on French beans.
  J.H. Nderitu , J.M. Kasina , J.W. Kimenju and F. Malenge
  This field study was conducted to evaluate the efficacy of two synthetic insecticides (Imidacloprid 350 g L-1 (Gaucho FSR) and Lambda-cyhalothrin 17.5 g L-1 (Karate 1.75 ECR), two neem products (Azadirachtin 0.15%w/w (AchookR) and Azadirachtin 0.6% w/w (Neem extractiveR) and a spray alternation of Azadirachtin 0.6% w/w and Lambda-cyhalothrin, in the management of aphids (Aphis gossypii Glover) infesting okra (Abelmoschus esculentus L. Moench). The crop was established in two seasons, December 2003-March 2004 and February-May 2004 at Kibwezi, Eastern Kenya. Imidacloprid was applied as a seed dresser while the other insecticides were foliar applied. The population of live and parasitized aphids was monitored on the leaves and pods of the plants for 9 and 7 weeks, respectively. The number of live and parasitized aphids was significantly (p<0.05) lower in plots treated with Imidacloprid, causing more than 95% aphid reduction. Plots treated with spray alternation of Lambda-cyhalothrin and Azadirachtin 0.6% had higher pest infestation than the other treated plots. Plants in Imidacloprid-treated plots had slightly higher yields than in other treatments. The results of this present study show that neem products are as effective as the synthetic insecticides in the management of aphids infesting okra. The study provides the best alternative of managing aphids` pests in okra that can reduce both the cost of production and chemical residue levels in the produce.
  J.H. Nderitu , E.M. Wambua , F. Olubayo , J.M. Kasina and C.N. Waturu
  Nine French bean commercial varieties and over ninety breeding lines were assessed to ascertain their susceptibility to thrips (Megalurothrips sjostedti Trybom and Frankliniella occidentalis (Pergande). Samples of thrips infestation were collected after anthesis at weekly intervals for four weeks. Evidence from the study showed significant differences among the French bean cultivars and breeding lines in thrips infestation. The cultivars had higher thrips infestations compared to the breeding lines. Pod damage score also differed significantly among the varieties with cultivar Harricot 05 recording the highest thrips damage score (2.84).
  V.M. Kega , M. Kasina , F. Olubayo and J.H. Nderitu
  Current pest control methods rely on a pesticide dominated paradigm and there is need to adopt a more ecological approach based on renewable technologies such as host plant resistance and natural biological control, which are available even to resource poor farmers. Resistant cultivars complement natural enemy action in lowering pest infestation while intrinsic rate of increase of pest species on resistant varieties is lower. An experiment whose aim, was to test whether the African white rice stem borer (Maliarpha separatella), can be managed by use of resistant rice varieties in combination with entomopathogenic nematodes was set up at Kenya Agricultural Research Institute, Mwea. The study was arranged as a 4x4 factorial design and each treatment replicated three times. First factor was rice cultivars at four levels, resistant cultivar (M27615), second resistant cultivar (M27628), the highly susceptible but tolerant cultivar (M27608) and commercial check Basmati 370 variety, which were planted in 1x1m experimental plots. Second factor was application of EPN (Hetrerorhabitidis indica) as a suspension in distilled water to the cultivars at four different times after they were transplanted (no application, 3 weeks after transplant date (WAT), 5 WAT and 6 WAT. Results showed that M. separatella infestation was lowest on cultivar M27615 where H. indica was applied at 3 WAT, while cultivar M27608 had the highest yield despite high number of white heads and stem tunneling indicative of high levels of M. separatella infestation. The findings showed that host-plant resistance and EPNs can be integrated to manage M. separatella infestation (250 words).
  V.M. Kega , J.H. Nderitu , M. Kasina and F. Olubayo
  Information on the population fluctuation of African white rice stem borer (Maliarpha separatella Ragonot), which is a major rice pest in Kenya, is not known. Availability of such information can assist in the development of an integrated management strategy for the pest. Therefore, a study was conducted at Mwea irrigation scheme in Central Kenya, to investigate the influence of irrigation water provision and cropping systems on population of M. separatella. Farmer fields in different parts of the scheme were sampled every fortnight. The farms represented three irrigation water provision schedules and three cropping systems regimes. The irrigation water provision schedules were, System of Rice Intensification (SRI), flood irrigated (conventional method) and sporadic irrigation. The cropping systems were main season crop (conventional method), double crop and ratoon. Water provision schedules were treated as main plots, while cropping systems were the sub plots. Results showed that the highest percentage of white heads (13.66) occurred in areas, where rice was double-cropped and where, there was sporadic water provision (9.70). There were no significant differences in the number of white heads (empty panicles) between the on-season (6.37) and ratoon (4.25) cropping system. There were also no differences between flood (4.42) and System for rice intensification (5.48) methods of irrigation. This study demonstrates that irrigation methods and cropping systems greatly influence fluctuation of M. separatella infestation and suggests that in case of double cropping it will be necessary to control the stem borer and efforts should be made to ensure that farmers synchronize planting dates.
  V.M. Kega , F. Olubayo , M. Kasina and J.H. Nderitu
  Information on losses caused by the African white rice stem borer, Maliarpha separatella rag, which is an important rice pest in Kenya is scanty. The development and implementation of effective pest management strategies relies on accurately defined Economic Injury Levels (ElL) for that pest. Investigations were, therefore, conducted to determine yield losses caused by M. separatella and economic injury level of the pest. The experiment was conducted in an insect proof screen house at Kenya Agricultural and Livestock Research Organization, Mwea station. The experiment was arranged as a (2×6) factorial design and each treatment replicated three times. First factor was time of infestation at two levels, early and late which was 3 and 6 weeks after transplant date, respectively. Second factor was infestation rate at six levels (0, 1, 2 4, 6 and 8 egg masses). Results indicated that infestation levels of 1, 2, 4, 6 and 8 M. separatella egg masses at early infestation resulted in grain yield losses of 59.8, 83.2, 84.8 90.2 and 90.9%, while losses of same infestation levels at late infestation was 34.3, 52.1, 63.4, 81.8 and 80.8%. There was a strong positive relationship between yield loss and M. separatella population levels, (y = -0.214.29x+ 1693.4, r2 = 0.8416). On the basis of cost benefit ratio, the economic injury level was 6 and 8 egg masses per square meter in the early and late infestation, respectively. The action threshold for early infestation was 4 egg masses and 6 egg masses for late infestation.
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