An infestation of armyworms, a pest that has hit maize fields in southern Africa, has spread across Malawi, a senior government official said on Tuesday. "The armyworms have now spread affecting all the 28 districts (and) threatening the crop for this year ...we are prepared and we will put it under control," Erica Maganga, principal secretary in the ministry of agriculture, told Reuters. The outbreak of fall armyworms - an invasive Latin American species which is harder to detect and eradicate than its African counterpart - has erupted in Zambia, Zimbabwe and Malawi and follows a crippling El Nino-triggered drought which scorched much of the region last year. A year ago, Malawi successfully contained an armyworm invasion that affected seven districts. "We are confident we will stop the spread as we experience more rains and more farmers use the pesticide that we have been distributing," Maganga said. She added the ministry was still assessing how many hectares had been affected. Earlier this month the government said 2,000 hectares of maize had been destroyed but the outbreak then was restricted to nine districts. Malawi's maize crop, the staple grain, was devastated last year by the regional drought. About 6.5 million Malawians, more than a third of the population, are dependent on food aid until this year's harvest in March, according to the United Nations' World Food Programme. The armyworms are caterpillars that "march" across the landscape in large groups feasting on young maize plants.