The fall armyworm is a destructive caterpillar that is indigenous to the Americas, the 'fall' referring to the season during which it tends to migrate to the United States.
It was only spotted in Africa last year but has already left a trail of destruction which is threatening food security in many parts of southern Africa.
The pest targets maize, sorgum, soya beans, groundnuts and potatoes. Zambia says 124,000 hectares (306,000 acres) of its crops have been destroyed. In December 2016, the country ordered the national air force into action to control the plague.
In a statement last week, the Food and Agricultural Organization (FAO) said "preliminary reports indicated the possible presence (of the pest) in Malawi, Mozambique, Namibia, South Africa, Zambia and Zimbabwe."
Essential for food security in large parts of Africa, maize is particularly vulnerable to the larvae of the fall armyworm, which attack the crop's growing points and burrow into the cobs.
South Africa says it is still assessing the damage but three of the country's nine provinces have been hit. Agriculture, Forestry and Fisheries Minister Senzeni Zokwana said they had positively identified fall armyworm in samples collected in Limpopo province.
Zokwana said his department was registering pesticides for use against the fall armyworm as "no pesticide was previously registered to be used against it."
He also told local radio on Tuesday he was convinced pesticides would be able to contain the outbreak.
The minister also stressed that South Africa would be taking part in an FAO meeting in Zimbabwe's capital Harare next week to draw up an emergency response to the threat.
He said the Department of Agriculture "realized that trans-boundary pests and diseases, especially migratory pests, threaten food security. Regional efforts are important to address these risks, to ensure that early warnings of these biological threats are in place."
Countries with confirmed outbreaks can face import bans on their agricultural products because armyworm is classified as a quarantine pest.
Mathew Cock, chief scientist at the UK-based Center for Agriculture and Biosciences International, said outbreaks could cause devastating losses and mounting debts for famers.
The fall armyworm from the Americas is also harder to detect and eradicate than its African counterpart
Jan-Hendrink Venter, a plant scientist with South Africa's Department of Agriculture, told DW it was spreading fast. "We are used to the common African armyworm. This is something new. It has a life cycle of 24 to 40 days. It's prone to the prevailing winds and can migrate very large distances.
A rural farmer in Limpopo province, who identified himself as Willi, says he belongs to a group of neighboring farmers who are extremely worried. He's concerned that the government might take care of commercial farmers and "forget us small farmers in rural areas so we might end up losing the whole crop."