A guide to seasonal changes in the distribution of armyworm infestations in East Africa

Abstract

The African armyworm, the larva of the night flying moth Spodoptera exempta (Walk.), feeds on young stages of cereal crops, sugar-cane and all types of grasses in some 30 countries of Africa, from Mauritania and Senegal in the north-west to Ethiopia and Somalia in the north-east, and southwards to Namibia and South Africa. Between 1960 and 1982, outbreaks of armyworms were recorded regularly in East Africa during the ‘outbreak season’ between November/December and June/July, often from southern Tanzania towards the north or north-west at monthly intervals. Analysis of occurrence of outbreaks in Tanzania, Kenya and Uganda in the 1971/72–1973/74 seasons, and rainfall records in Tanzania for 1969–1975, showed that the occurrence of armyworms in Tanzania coincided with the onset and northward progression of the rains up to Kenya and Uganda. Additional results from monthly maps, tables, graphs and histograms of armyworm occurrences in administrative units (Districts and Provinces) in Tanzania, Kenya and Uganda for 20 years (1960–1979), showed that the onset, progress and duration of armyworm attacks in all districts and provinces in each country, tend to follow certain geographical patterns which can be monitored through the use of insect traps and Agricultural Extension Services. In this way, coordinated surveillance of priority areas could enable farmers, pastoralists, Plant Protection and Pest Control Units of the Ministries of Agriculture to identify likely areas and periods of armyworm attacks, so that they could organize strategic or emergency control of armyworms with insecticides when the larvae are still young.