School of Agriculture and Biotechnology
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Item Effects of entomopathogenic fungus and spider plant intercrop in control of onion thrips and iris yellow spot virus(INNSPUB, 2018-06-30) Birithia, Rael Kayume; Subramanian, Sevgan; Muthomi, James Wanjohi; Narla, Rama D.Iris yellow spot virus (IYSV) is a major constraint to bulb onions production in Kenya. In search for alternative to synthetic insecticide, field experiments were conducted for two cropping seasons to evaluate the effectiveness of spider plant intercrop, Metarhizium anisopliae and carbonsulfan insecticide in the management of onion thrips and IYSV. Two onion varieties; Bombay red and Red creole were used. Randomized complete block design in a split plot arrangements was adopted. Results showed both varieties treated with entomopathogenic fungus recorded the least number of adult thrips while insecticide treated plots recorded the least larvae thrips. Insecticide, entomopathogenic fungus and intercrop significantly reduced IYSV incidence as compared to the control plots. Bombay red variety treated with fungus recorded the lowest severity and virus titer levels in the two cropping seasons. Adult thrips positively correlated with IYSV incidence in season one (r = 0.575; P <0.001) and two (r = 0.580; P <0.001). Red Creole treated with insecticide recorded the highest bulb onion total yield (10782.8 T/ha) and marketable yield yield (8314.8 T/ha) in the first cropping season. Entomopathogenic fungus treated plots outweighed other treatments in the second cropping season and recorded total bulb yield of 8503.7 T/ha and marketable yield of 7611.1 T/ha. Although, spider plant intercrop reduced bulb yield in both seasons, it contributed significantly in reducing onion adult thrips and increased food productivity. Metarhizium anisopliae and spider plant intercrops were found to be effective bio-pesticide and we suggest their inclusion in the integrated management strategies of vector thrips and IYSV.Item EFFECTS OF WEATHER ON THRIPS POPULATION DYNAMICS AND ITS IMPLICATIONS ON THE THRIPS PEST MANAGEMENT(Karatina University, 2008-06-30) Waiganjo, M.M.; Gitonga, L.M.; Mueke, J.M.Onion thrips, Thrips tabaci Lindeman, is the most destructive insect pest of the onion crop, Allium cepa L. worldwide. Both larvae and adults attack the onion crop at all stages of its growth, resulting in reduction of yield and quality. Despite the heavy losses incurred as a result of damage by the onion thrips, very little efforts have been made to develop an integrated pest management strategy for the control of the pest in many African countries. Field trials were conducted in four seasons at the Kenya Agricultural Research Institute (KARI) Mwea-Tebere farm in Kirinyaga District. Onion plants were planted periodically and thrips populations monitored weekly from onion plant samples and blue sticky traps for a full year under natural field conditions. The purpose of the trials was to assess the effect of weather on thrips population in onions with the aim of predicting thrips control requirements for a given climatic trend. Weather variables monitored included: rainfall, temperature, relative humidity and wind. Thrips occurred in the onion field and infested onions in all the crop seasons. However, there was significant (P=0.05) variation in thrips numbers between the crop seasons. Dry weather (30.3 mm rainfall) with moderately high temperatures (15.6-28.2oC) increased seasonal thrips numbers, while wet season (391mm rainfall) with moderately high relative humidity was negatively correlated with thrips numbers. Regression analysis (step-wise selection model) showed that minimum relative humidity was the only significant weather factor for predicting thrips infestation in the onion crop (R2 =0.15; y = 60.342-0.1022x). The results suggest that climatic trends can be used to determine the potential thrips control needs in onion production.