Zambia, Malawi and Zimbabwe are urging farmers to act fast with pesticides to halt the spread of armyworms now threatening crops.
Armyworms are a common pest, but this year's invasion has sparked particular concern.
In those three countries alone, the worms have destroyed thousands of hectares of maize — a staple food. El Nino-induced drought and flooding destroyed much of the previous two harvests, leaving nearly 30 million people in the region in need of food assistance.
"The problem is that if you have had, like we have had here in southern Africa, two droughts, it provides [a] conducive environment for the army worms to be very active when the rains come," said Chimimba David Phiri, coordinator for the U.N. Food and Agriculture Organization for Southern Africa.
Malawi first reported the armyworms at the start of January, in eight of the country's 28 districts. Now, officials say the worms have spread across Malawi.
"People in most parts of the country are now reporting incidents of some sort,” said Erica Maganga, principal secretary in the Ministry of Agriculture in Malawi.
She says efforts are underway to contain the worms.
"It's a pest that comes almost in every growing season,” Maganga said, “so we always pre-position pesticides in all the ADDs [Agriculture Development Divisions]. We are giving out cypermethrin to small-scale farmers whose gardens have been affected."
Maganga says owners of big farms are advised to buy the pesticides from agro-dealer shops.
Rose Chisowa, a farmer outside Malawi's capital Lilongwe, told VOA that she has almost managed to control the worms which invaded her rice field.
"I noted about the armyworms earlier,” she said. “Actually, I noted it on my rice when it was on nursery. So I bought some pesticides. I sprayed cypermethrin and it worked."
Zimbabwe is reporting the armyworms in seven of the country's eight corn-growing provinces.
But it is Zambia that has been the hardest hit. The country first registered the invasion of the worms last month in four provinces: Copperbelt, Central, Eastern and Lusaka.
Zambia has been using military planes to spray pesticides to highly affected areas.
Local media reports say the worms have destroyed 124,000 hectares of maize crops in Zambia, up from nearly 90,000 hectares last week.
VOA’s Sebastian Mhofu in Harare contributed to this report.