Etiology, epidemiology and control of bean scab caused by elsinoe phase Jenkins sp vulgare in Kenya
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The investigations done in this project on the pathogen Elsinoe phaseo Jenkins vulgare included etiology epidemiology and control. The pathogen attacks all parts of foliage. Symptoms on the stems are elongated raised lesions measuring up to on~ cm long.They coalesce to cover big portions of the stem. The lesions on the leaves are ashy grey, roundish to irregular measuring up to 4 mm. When the veins are attacked, the saves curve upwards. Roundish to irregular ashy grey lesions with brown to brick red margins are found on the pods. They coalesce to cover large portions of the pods . The pathogen is sub epidermal where a sci are borne in single locale. They contain eight ascospores which are 1-3 separate and measure up to 13.5 u X 7.5 u. The imperfect state (Sph2celoma sp.)occurs on the surface of the lesion. Conidia are borne in acervuli which cO~3ist of indistinct compact conidiophores. Conidia measure 2.6 u x 590 u. in diameter. Infection in beans was successful only in young leaves less than one week old. Older leaves became resistant. Out of thirty four legumes tested, Phaseolus vulg3ris. Pha3801us lunatus and Dolichos 1ab1ab were infected. 'Mexican 142' and 'Ree haricot' bean varieties were found resistant •. Epidemio1r-gy and control experiments on bean scab carried out at the University Field Station, Kabete which is cool and wet, and at Katumani research station which is warm and dry, showed that contact was an effective means of disseminating the pathogen. Dissemination by wind was less efficient and was greatest in the down wind direction. Disease intensity was compared in the two stations and was found to be more severe a4 Katumani than Kabete. The meteorological factors indicated that temperature, windrun, relative humidity and precipitation at the time of inoculation highly influenced the progress of disease in the two stations. Shorter incubation and latent periods raised the level of inoculate more quickly at Katumani than at Kabete and this also contributed to a higher disease level. In the later stages of the epidemic, the rate of disease progress in both areas depended more on the amount of healthy leaf tissue remaining. Diseased plants incurred yield losses up to 70% at Katumani and up to 40% at Kabete. In the chemical control experiment, it was further demonstrated that sprays of three Fungicides, namely, benlcte (methyl-l-(but,yl-carbamoyl) benzimidazol-2-yl carbami~e) a systemic fungicide, and manganese ethylene bisdithiocarbamate) and copper oxychloride, gave higher yields than the control. Benlate was the best and gave ap~roximately 13% higher yields than the control. Benlate and copper oxychloride could be economically used because they gave Ksh. 635/ha and Ksh. 392/ha respectively above the control. Dithane M-45 gave a negligible arno un +t- or~ Ksh. 8.