Agriculture Minister George Chaponda told Reuters that the country was confident about dealing with the outbreak because it successfully contained an invasion last year.
Army worms are caterpillars that "march" across the landscape in large groups feasting on young maize plants, wiping out entire fields.
Neighbouring Zambia is also dealing with the outbreak and has deployed its military to deal with the threat. Zimbabwe is also affected.
Around 6.5 million Malawians, over a third of the population, are dependent on food aid until this year's harvest in March, according to the UN World Food Programme, the report says.