maize downy mildew, % incidence, Sudan and Sahel savannah agro-ecological zones
The incidence, distribution and prevalence of downy mildew in maize were investigated during the
2008 growing season following a planned–two time survey across the Sudan and the Sahel savanna agro-ecological zones of Nigeria. The occurrence of the disease was investigated in 102 and 120 farmers’ fields in 34 and 40 locations in the first and second surveys respectively. Average incidence (%) of the disease was obtained from a sample of 100 plants each from three farms per stop; each farm representing a replicate. Simple random sampling technique was employed in the
selection of plants. Results of the survey have revealed that 20 out of the 34 locations visited during the first survey had maize with early symptoms of the disease while only 4 out of the 40 locations visited in the second survey was having the symptoms of the disease. The incidence of the disease was 8.20% and 1.12%, in the first and second survey respectively and therefore
significantly different (p>0.05) indicating that the disease was more prevalent at seedling than at grain filling stage which is an indication of the absence of certified, sorghum downy mildew (SDM) free seeds in most of the regions surveyed. The incidence was also higher in the Sudan than in the Sahel savanna (16.28% and 3.28% first and second visits respectively). This might be probably
because of differences in climate of the two zones and the fact that maize was grown more in the Sudan than in the Sahel savanna zone. Although the incidence was generally low, proper measures should be taken to avoid unexpected epidemic of the disease in the future.