When farmers reported fields full of dead caterpillars covered in a mysterious white substance, scientist Letodi Luki Mathulwe of South Africa's agriculture department went to investigate. It turned out the white substance was a natural fungus killing fall armyworm, one of the most destructive pests for farmers in Eastern and Southern Africa.
The 2025 fall armyworm outbreak began in northern Africa and by April had reached KwaZulu-Natal province in eastern South Africa, where Mathulwe works. She received frantic calls daily from local farmers about the worms appearing throughout their fields. When she visited Kikuyu grass pastures—vital for cattle grazing—she made a key discovery: “Something was naturally killing the worms. I was curious because in other areas the worms were alive and damaging the grass, but here they were dead.”
An entomologist who had studied using fungi to control pests, Mathulwe collected samples of dead worms and the fungus for her laboratory in Pietermaritzburg. The findings, published in a specialist journal, showed that this soil fungus could indeed be used against fall armyworm. This is a major breakthrough since, previously, chemical pesticides worked only in the early stages of the worm's life cycle, with no effective method for mature larvae.
Fall armyworm not only devastates staple crops like maize and sorghum but also releases chemical compounds in grass that can make livestock sick. A 2017 outbreak destroyed up to 40% of Zambia's maize harvest. The pest causes heavy losses for farmers, drives up food prices, and strains government budgets. Last year's outbreak affected farmers in Zimbabwe, where inflation hit 736% in 2024, and Malawi, where it reached 35% in 2024.
The fall armyworm causes most damage in its larval stage, but once it becomes a moth, it is hard to control and can migrate far. Mathulwe hopes the research will lead to a biological product using the soil fungus that can be sprayed during outbreaks. “When we found this fungus, we realized we could develop it into a product for the next outbreak. That would be wonderful and would remove farmers' fear when worms appear in their pastures,” she said.
Despite the promising initial results, Mathulwe noted that more research and trials are needed before the product reaches farmers. “I think this will bring great hope to farmers, because it means their livestock won't get sick if we can control the worms in the pasture.”
