The African armyworm Spodoptera exempta is a major episodic migratory crop pest over much of Eastern and Southern Africa. Control of this pest has been reliant on the use of synthetic chemical insecticides. However, this approach fails to protect poor farmers and is becoming unacceptable for environmental and cost reasons. A programme of field trials was conducted in Tanzania to evaluate the endemic baculovirus, the S. exempta nucleopolyhedrovirus (SpexNPV), as an alternative control. Field trials demonstrated that both ground and aerial application of SpexNPV to armyworm outbreaks on pasture can initiate outbreaks of NPV disease and population collapses. The SpexNPV was effective when applied at 1×1012 occlusion bodies (OB) per hectare if applied to outbreaks early, when larvae are in I–III instar—mass mortalities appear 3–10 days post treatment. The data from these trials indicate that SpexNPV can have a potential role as a substitute for chemical insecticides in strategic armyworm management programmes.