School of Agriculture and Biotechnology

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Author: search.filters.author.Mueke, J.M.Has files: Yes

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    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.
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    SUSCEPTIBLE ONION GROWTH STAGES FOR SELECTIVE AND ECONOMIC PROTECTION FROM ONION THRIPS INFESTATION
    (Karatina University, 2008-03) Waiganjo, M.M; Mueke, J.M.; Gitonga, Linus
    The growth of the bulb onion is subject to significant stress and yield reduction caused by sap feeding onion thrips. In Kenya, the general control recommendation is to spray the crop with insecticides as soon as the pest appears and to continue thereafter, throughout the crop season. The practice is expensive and environmentally hazardous. Two field trials were conducted at the Kenya Agricultural Research Institute (KARI) Mwea-Tebere farm to identify the growth stages most susceptible to onion thrips infestation that would provide the highest economic benefits to the onion grower by managing thrips, with the aim of promoting need-based onion pesticide application. The trial design was randomized complete blocks of 16 treatments replicated three times. The treatments constituted insecticide treatments at different onion growth stages and frequencies. Thrips density/plant was estimated weekly through a destructive cutting and bagging method. Yield gains due to the application of the protection regimes were calculated and the marginal returns estimated as the income of yield gain divided by the cost of the control option. Thrips infestation was significantly (p=0.05) higher in the unprotected plots than all the protected plots in the first and second trial and resulted in significant yield losses of 59 and 29%, respectively. A significant onion yield response to thrips infestation was observed during the 2nd month (bulb-formation) and 3rd month (bulb-enlargement) after transplanting, but no significant response was observed in the 1st month (pre-bulbing) and 4th month (maturation) respectively. Onion protection only during the bulb-formation stage resulted in higher marginal returns than full season pesticide application. The studies suggested that control recommendations for onion thrips could be refined to optimize selective pesticide use in Kenya.
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