From poison to biology: how nematodes could help Kenyan farmers defeat the fall armyworm
Felix Johnson stands in the morning heat of Kilifi County on Kenya’s coast, pointing to his maize plants. In the leaf axils sit the caterpillars of the fall armyworm (Spodoptera frugiperda), some finger-length. Johnson, 31, cultivates maize on just under two hectares. Every one to two weeks he sprays insecticide—like most smallholders in the region, using a backpack sprayer in temperatures of around 40°C. Many of his neighbours do so without gloves or masks. “If you spray today, after two, three, four days the pest is back again,” he says.
Johnson is one of many thousands of smallholder farmers in Kenya who have been battling a pest that spread across much of the continent within months of its 2016 arrival. Eighty-one per cent of surveyed farms in five Kenyan counties report heavy infestation. The fall armyworm attacks not only maize but over 350 plant species—including many crops, from millet and rice to sugar cane and pasture grass. For many, this means reduced yields and thus lower incomes. Those who grow maize—Kenya’s most important staple food—can hardly avoid it.
This is precisely where a Swiss-Kenyan research project intervenes. Funded by the Swiss National Science Foundation (SNSF) and the Swiss Agency for Development and Cooperation (SDC) under the SOR4D programme, it is a collaboration between four partners: the International Centre of Insect Physiology and Ecology (icipe) in Nairobi, the research groups of Sergio Rasmann and Ted Turlings at the University of Neuchâtel, CABI Switzerland and Dudutech/Bioline, a commercial producer of biological pest control products from Kenya’s Rift Valley.
Rather than attacking the pest with chemical insecticides, the project team deploys a natural antagonist: entomopathogenic nematodes. These microscopic roundworms penetrate the larvae of the fall armyworm and kill them from within. The Swiss partners in Neuchâtel possess considerable expertise in developing such biological pest controls. Icipe adapts the method to local conditions and works with Dudutech/Bioline to find ways of marketing it to farmers.
The pesticide trap
“We thought that if we used higher doses, it would work faster. That’s not true,” says Lucky Nzilani Mutua, 28, a farmer and teacher from Makueni County. Like many smallholders, she sprays every one to two weeks against the armyworm, as well as against fungal infections. When she could no longer tolerate the consequences—declining bee populations and, by her own account, lung and heart problems—she converted her kitchen garden to organic cultivation for household consumption. “Since we switched, I haven’t been to hospital for two years.” But for her income she remains dependent on chemically treated maize and vegetable cultivation. “Sometimes you do things, you wouldn’t inflict on yourself,” she says.
The extent of the problem is revealed by soil samples from a scientific survey in the five affected counties: the 125 farms examined yielded 61 different pesticide residues—including substances classified as “extremely hazardous” and active ingredients now banned in Kenya. Since the armyworm’s arrival in 2016, pesticide use on maize has risen dramatically. Protective equipment is rarely worn in extreme heat. Residues on freshly harvested food have long since become a health problem for consumers as well. One telling detail: Kenya’s export farms have not used highly toxic Class I pesticides for over 20 years—because European buyers demand this measure. Domestic market produce often faces no comparable controls.
Suncream for the nematode
The research team relies on a biological antagonist: entomopathogenic nematodes—microscopic roundworms that live in soil, penetrate insect larvae and kill them from within. The method is used worldwide in plant protection, mainly against root pests. They have rarely been used aboveground, but this is now possible thanks to a newly developed gel-based formulation. Still, under equatorial conditions of intense heat and UV radiation, these sensitive organisms reach their limits.
“Without additional protection, the nematodes are damaged too quickly in the field,” says Fathiya Khamis, who coordinates the project at icipe. In practical terms, this meant researchers had to protect the nematode against UV with something akin to suncream, such as titanium dioxide and rapeseed oil, which also serves as an inexpensive carrier substance. Building on a formulation from the University of Neuchâtel, the team developed a gel that protects the nematode and can be applied with a standard backpack sprayer, just like a pesticide, but is harmless to humans and the environment.
“We thought it would be plug-and-play—we take the formulation from Neuchâtel, and voilà, it works here,” says Khamis. “But it wasn’t like that.” The commercially available nematodes, a powder product from Kenyan partner Dudutech already on the market against other pests, did not work against the armyworm. The team had to collect dozens of nematode isolates from Kenyan soils and test each individually against armyworm larvae in the laboratory to find the species that reliably kills the pest. In the end, it was an isolate from Dudutech’s own collection (Steinernema carpocapsae) that showed the highest efficacy.
Three per cent of the gel in the Neuchâtel formulation consisted of a common thickening agent (carboxymethyl cellulose), a viscous mass best applied drop by drop to individual plants. For the backpack sprayer used by smallholder farmers, this was far too thick. Only when the team reduced the proportion to 0.5 per cent did they achieve a more fluid formulation—thin enough for the sprayer nozzle, thick enough to keep the nematodes attached to the leaves.
“Once it becomes sprayable, like a pesticide but safer, acceptance will rise,” says Khamis. The new formulation must prove itself this summer in field trials on farmers’ holdings. But commercial readiness—product registration, commercial production, distribution networks—will likely take several more years.
A network between laboratory and field
Even the best product is of little use if it does not reach the farms. The project therefore relies on knowledge transfer from farm to farm: 25 “Trainers of Trainers” (ToT), five per county, were trained at icipe. Back in their communities, they convert their own fields into demonstration plots. They remain connected with each other and the researchers via WhatsApp groups. Felix Johnson is one of these trainers. During his visit to icipe, he put it succinctly: “We are here to get new technologies so we can avoid the chemicals.”
Data from initial field trials promises success: in the greenhouse, the best nematode isolate achieves efficacy comparable to chemical pesticides. But expectation management among farmers could prove a major hurdle. It takes about two days, not hours, for the nematodes to kill the pest. The “knockdown effect”, or the immediate, visible death of the pest after spraying, does not exist with nematodes. Farmers who see no effect after half a day may well resort to chemicals again in doubt. “As trainers, we will specifically pass on knowledge about the peculiarities of biological control,” says Felix Johnson.
From laboratory to market
Developing biological agents is one thing. Bringing them into the daily routine of smallholder farmers—on time, in appropriate package sizes and at an affordable price—is the second, often more difficult task.
Catherine Gacheri from partner company Dudutech/Bioline, responsible for commercial scaling, says: “When the project ends, it’s up to us to ensure that farmers can actually get the product.” For Dudutech, this means mass-producing nematodes, ensuring quality, and establishing storage and transport routes. Currently, nematodes as a product have a shelf life of only about one month. The gel formulation should extend shelf life to about three months—crucial in determining whether a product can reach rural agricultural shops at all.
Biological control is more expensive than chemical pesticides, Gacheri acknowledges. In the long term, it could still be cheaper, if one considers the total cost of a pesticide cycle: repeated spraying, health costs, resistance development. Reliable cost-benefit data—what does a farmer save per season specifically?—is still outstanding. The socio-economic evaluation is planned for after the first field season. Until then, the cost argument remains a promise.
When asked at a training day at icipe whether he would be willing to pay more for the biological agent than for a pesticide, one farmer does not hesitate: “It’s better to have an expensive solution than the diseases we’re experiencing now. Cancer is more expensive.”
More than a product
Biocontrol alone will not defeat the armyworm. Researchers recommend it as part of an integrated approach: supplemented by intercropping, targeted border planting or push-pull, a strategy where companion plants repel pests from maize and attract natural enemies.
For such an approach to take effect, it needs more than a good product. It requires a political framework that not only tolerates but actively favours biological alternatives. In Kenya, this framework has existed formally since 2024: with the National Agroecology Strategy for Food System Transformation (NAS-FST) 2024–2033, Kenya has become one of the first countries in sub-Saharan Africa to adopt a ten-year strategy for transforming its food system.
It is to be implemented at provincial level, and some counties such as Murang’a and Vihiga are leading with their own agroecology laws. The pesticide bans of June 2025, which led to 77 products being withdrawn, 202 restricted in application and 151 others placed under review, are part of the same movement. Research shows that banned substances continue to circulate under new brand names. But the direction is right, and creates a market without which biological alternatives like nematodes would have no chance.
Whether the approach becomes established beyond the project’s end also depends on the institutional framework. The project works with the Kenya Plant Health Inspectorate Service (KEPHIS) and county agricultural ministries; agricultural extension officers accompany fieldwork and training. Product registration with the Kenyan pesticide authority is Dudutech’s responsibility, a process that still lies ahead and typically takes time.
Much speaks for continuity even without project funding. Dudutech has a commercial interest in the product as a company and will remain in the market even without research funds. And the county agricultural ministries, whose extension officers have accompanied the project from the start, maintain a permanent presence in the communities, an institutional anchor for the training network.
Felix Johnson will not make this his primary concern. He has enough to do getting his two hectares of maize through the next season. But if the nematodes deliver this year in field trials what they promised in the greenhouse, he can fill his backpack sprayer with nematodes rather than pesticides, without a mask and without concern for his health.
