A study of cercosporao zeae-maydis on maize (zea mays L.) in relationto its viariability and control in Zambia
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Maize (Zea mays L.) is an important crop in Zambia but it is being threatened by a number of foliar diseases. In Zambia, gray leaf spot caused by Cercospora zeae-maydis has become a serious foliar disease of maize in the last four years.The assessment of the variability of Cercospora zeae-maydis was done by taking samples from the three agro-ecological regions of Zambia. Samples were collected from Livingstone, Choma, Kabwe and Ndola. Four fields, which'had natural infection of Cercospora zeae-maydis, were randomly sampled for each site. Diseased leaves were collected from the plants when the crop was nearing physiological maturity.Sections of the diseased maize leaves were incubated to allow for the growth of the pathogen. Measurements of the conidial size were done after five days of incubation at 25 °C. An analysis of variance of size of conidia revealed significant differences within and between the agro-ecological regions of Zambia. The variability observed could be attributed to the differences in the climatic conditions in the agro-ecological regions.A susceptible variety, SC 401, was used to assess the effectiveness of Early Impact fungicide (150g carbendazim and 94g flutriafol per litre) on the control of gray leaf spot disease on maize. The experimental sites used were Mt. Makulu Research Station and University of Zambia School of Agriculture field station. Three treatments and a control were used. The experiments were replicated three times in a Completely Randomised Design.Spraying commenced at 62 days after emergence of the maize crop when the disease index was 35. A second spray was applied 21 days after the first fungicide application. Disease index increased on the control plots. For those that received a single fungicide application, the disease index decreased initially but increased again subsequently. Those that received two or three fungicide applications demonstrated a decrease in the disease index throughout the experimental period.Early Impact can effectively control gray leaf spot disease on maize with an economic benefit of 425% if a single fungicide application is made at the appropriate time. However, if the disease pressure is high, two fungicide applications would be necessary to control gray leaf spot on maize.