The fall armyworm is an invasive pest, a moth native to the Americas that was found for the first time in early 2016, in the West and Central African countries of Benin, Nigeria, São Tomé and Príncipe, and Togo. The moth is a voracious eater of corn along with 80 other plant species including millet, rice and sorghum. It is also a strong and fast flyer, and as of summer 2018, it had been confirmed or reported in every sub-Saharan African country. More recently, it was confirmed in southern India, marking its arrival on the Asian continent.
In Africa, the fall armyworm is now here to stay with no chance of eradication, only damage mitigation. Now that it has spread to India and will likely show up soon in other Asian countries, sustainable and effective control methods are vital.
When an invasive, agricultural pest shows up in a new place, the response often involves the spraying of chemical pesticides. If an insect is causing damage, the thinking is often poison: the insect and stop the damage. In practice, however, it is rarely, if ever, that simple. Chemical pesticides can cause damage to both human and environmental health and are also expensive, putting them out of reach for smallholder farmers in developing countries.
Most African farmers who grow corn are subsistence farmers, growing crops for their own consumption. So when the fall armyworm showed up in West Africa and spread quickly to the rest of the sub-Saharan continent, decimating crops that these farmers rely on for food, they panicked, leading many governments in countries such as Kenya, Tanzania and Uganda to provide or subsidise pesticides, which many farmers use without proper training.
“The immediate reaction on the part of national governments is to go to pesticides,” says Allan Hruska, the Principal Technical Coordinator for fall armyworm at the United Nations Food and Agriculture Organization (FAO). “There’s political pressure to do something immediately, so the quick reaction is to go to pesticides. Donors give money to governments and they buy pesticides and either give them away or apply it themselves.”
Pesticides are also prohibitively expensive. With governments freely handing them out in the 2016/2017 cropping season, there was a big increase in their usage with around 60-70% of farmers using them in certain countries – in Ghana, 71% used pesticides and in Zambia, 60%. But in the 2017/2018 season, when farmers had to procure their own pesticides,the numbers went down to 53% in Ghana and 43% in Zambia according to a CABI report that will be published this year – although this usage is still relatively high.
And because these farmers do not generally have a lot of experience with pesticides and received no training from government in their use, they often spray them incorrectly or unsafely, threatening their own health as well as the health of the environment. A 2017 study from the UN found that pesticide poisoning was responsible for 200,000 deaths worldwide.
But, many farmers have found that the chemical pesticides are not effective against the fall armyworm. In addition, pests build up resistance to pesticides that are commonly sprayed. This has happened with the fall armyworm in its native habitat in the Americas, and scientists believe with time it could happen in Africa as well.
“A lot of the farmers we talked to who did try pesticides say that [they] don’t work,” says Paul Van Mele, Director of Agro-Insight, an enterprise that produces farmer-to-farmer training videos in developing countries. Agro-Insight is also co-founder of Access Agriculture, an NGO that makes training videos widely available to farmers on a variety of agricultural subjects. “Even if they spray…two weeks later when new leaves emerge, [the leaves were] already damaged inside the whorl, so the farmers think it’s not working and they just keep spraying.”
In addition, pesticides are indiscriminate killers, meaning that they will also kill any natural enemies of the fall armyworm that are present on the corn plant. Integrated pest management (IPM) is an important part of successfully controlling the fall armyworm, so beyond not being effective as a chemical control, pesticides may actually have an adverse effect because it will leave the fall armyworm without any natural predator that could keep the pest’s numbers down.
The value of traditional methods and innovation
One of the factors that makes fall armyworm so difficult to kill on corn is the structure of the plant. Corn plants contain a whorl, a group of leaves wrapped around the stem, which provide a cozy place for the larvae to hide from chemical pesticides. With pesticides both an ineffective and expensive option, farmers have begun to look at more traditional methods for pest control, making use of relatively cheap, locally-available, non-toxic ingredients and materials which they already have access to.
Access Agriculture recently put out two videos on the fall armyworm for farmers, one to help them identify the pest and another to train them in some of the traditional control methods. “Farmers tend to innovate,” says Roger Day, programme executive for the Centre for Agriculture and Bioscience International (CABI)’s Action on Invasives programme. “If you’re in a difficult spot, you’ll probably start trying things.”
For example, many farmers are using ash or sand or salt or soil placed directly in the whorl to suffocate the larvae hiding in the plants. Across the continent, farmers use different kinds of ash depending on what’s available, and sometimes they use a mixture of the above materials. Use of soil, ash, sand, or salt is already relatively common in Central America, one of the fall armyworm’s native habitats, so Hruska was pleasantly surprised when he saw African farmers employing the same techniques on their own without having been introduced to the method.
Ivan Rwomuhana, Senior Scientist for Invasive Species Management with CABI says he’s heard from farmers who have had some success by simply spraying their plants with water, trying to mimic the effects of heavy rain and knocking the pests to the ground.
Other traditional methods include smearing lard on the stalks of corn plants to attract ants to predate on the fall armyworms; making botanical mixtures using plants such as Mexican marigold, pepper, aloe vera and bitter weed, to put on the maize plants that will repel the fall armyworm; use of fungi and insect predators against the fall armyworm; disrupting the fall armyworm’s mating by using pheromone lures; and the application of Neem extract. Neem is a tree that is common in many parts of Africa and its leaves contain a natural insect repellant called azadirachtin.
Intercropping, which is planting corn along with other plants that can attract the fall armyworm away from the corn, has also shown to be effective against the fall armyworm. One intercropping method that has been shown as particularly effective is the Push-Pull method, developed by the International Centre for Insect Physiology and Ecology (ICIPE). This method involves planting corn alongside Desmodium, a weed that repels certain predators, including in this case, fall armyworm. The edge of the field is also lined with Napier grass to attract predators away from the corn.
And one of the cheapest, albeit time consuming, methods is simply hand-picking – going from plant to plant, finding the armyworms, picking them off the corn plants and squishing them between one’s fingers. In some places, entire communities are engaged in the task of combing the fields and hand-picking the pest.
Already organizations like CABI and FAO are trying to spread word and provide training in these traditional methods for farmers. FAO runs Farmer Field Schools to train farmers in identification and local control methods and CABI is conducting farmer surveys in Ghana and Zambia to find out what kinds of methods farmers are already employing. However, with such a diverse array of tactics to tackle fall armyworm, it can be difficult to find a set of recommendations that could be considered ‘best practice’.
“One thing we found with the fall armyworm is people saying that we can’t recommend anything if it’s not scientifically proven,” says Day, “which is good on the face of it; but then if you’re saying ash, for example, you’d have to try every kind of ash to make a recommendation. When you’re using a pesticide, it’s easy to know the active ingredient.”
To this end, CABI will soon begin trials on ash and a few other traditional methods in Ghana and Zambia. But of course, with thousands of types of trees, it would be impossible to conduct experiments with all the kinds of potential ash.
For Day, while it is important to try and validate these methods, it is more realistic to educate and empower farmers to find things out for themselves, and then, let them take the lead.
Photograph: Paul Van Mele
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