The University of Greenwich

Fighting armyworm in Kenya and Tanzania

Armyworm are caterpillars of a night flying moth which lays its eggs on grasses and cereal crops. Within a few days the larvae hatch, with up to 1000 caterpillars occupying each square metre. In such numbers, they are able to devastate an area of grassland or crop in a few hours, before characteristically 'marching' to the next source of food. In Tanzania, serious outbreaks of armyworm occur nine years out of ten, causing up to 90% losses of crops and pasture. As the number of caterpillars and moths increase, the plague spreads north through Kenya to Ethiopia, and even Yemen, or south to Malawi, Zambia and Mozambique.

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  • Disaster ReliefDisaster Relief
  • Education/Training/EmploymentEducation/Training/Employment
  • Environment/ConservationEnvironment/Conservation
  • Health/WellbeingHealth/Wellbeing
  • Poverty Alleviation/ReliefPoverty Alleviation/Relief


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Farmers have the choice to either pay the $10 per hectare needed for pesticide application, or face the threat of total crop loss. There is a lower cost solution in the form of nuclear polyhedrosis virus, or NPV. The virus occurs naturally in armyworm caterpillars, but generally spreads too late and too slowly to prevent crop loss. Mass-production of NPV as a powder, instead of chemical sprays, has proved to be an effective tool against the armyworm. Since the virus, once sprayed, spreads naturally in the armyworm population, the method is ideal for tackling the dispersed pest and is of no danger to humans, livestock or other insects. Early application during the first few days after the larvae hatch is essential if adequate crop protection is to be achieved. This requires early warning of outbreaks through regular monitoring of moth numbers. Monitoring in Tanzania was formerly done by government employees who reported back to a central control office from where information was sporadically distributed to farmers. Surveys have shown that most farmers have a poor understanding of armyworm, do not know what to look for and do not know what to do about it. Crucially, the national forecasts hardly ever reach them. In the last three years a community-based monitoring system has been successfully implemented in several high-risk districts. Armyworm forecasters have been elected and trained to monitor male moth numbers through the use of pheromone traps. A villager operates a single trap, collects data and makes a local armyworm forecast according to some simple rules. This process of community-based armyworm forecasting (CBAF) has proved to be sustainable. The first participating villages were trained in 2002 and they continue to operate their own forecasting systems with minimal intervention by local Ministry of Agriculture staff. This system now needs to be implemented on a larger scale. A national programme is needed to formulate and distribute the NPV powder and roll out the local forecasting method. Two hundred villages could benefit over a three year period. A funding initiative of £1.5 million over five years is required to implement the scheme to reach all the villages that could benefit in Kenya and Tanzania. Even if technology penetration achieved only 25%, the potential benefit would be approximately £10 million over the next decade.