Summary: Maize lethal necrosis (MLN) is a viral disease of maize caused by the combination of Maize chlorotic mottle virus (MCMV) and one of viruses in the Potyviridae family such as Sugarcane Mosaic Virus (SCMV), Maize Dwarf Mosaic Virus (MDMV) or Wheat Streak Mosaic Virus (WSMV). In Rwanda, the disease was identified in 2013; it was reported to be caused by a combination of two viruses MCMV and the potyvirus Sugarcane mosaic virus (SCMV). MCMV is new in the country and is thought to be transmitted mechanically or by insect vectors (thrips and beetles) as well as seed while SCMV is endemic. Symptoms of MLN disease include leaf mottling and necrosis, stunting and failure to produce tassels, immature ear husks showing yellow streaks, ears appearing physiologically mature, kernels inside are still at milk stage while the rest of the plant is still green. Infected plants form small cobs with few grains or on grains; necrosis of young leaves in the whorl before expansion leading to the death of the whole plant.