Nov

How do we fight the Fall armyworm, the new wound of African agriculture ?

Feeding on sorghum in Niger

Two years after its first detection in West Africa, this invasive caterpillar is threatening the food security of millions of small farmers in over 30 African countries.

To solve the future food needs in sub-Saharan Africa, entomologists must be a critical part of the puzzle. From Nigeria to Ethiopia, South Africa to Chad, African smallholder farmers often face severe crop losses from damaging bugs from locusts to cassava’s whiteflies, cowpea pod borers or maize and sorghum stem borers. According to the Center for Agriculture and Biosciences International (CABI), pests, (some emerging due to climate change or shifts in land use), reduce African crop harvests by 50%. Most smallholder farmers don’t have the ability to diagnose crop problems quickly and often have no means or knowledge to control these pests. With climate change and increased movement of goods and people, emerging pests will worsen an already serious problem.

Now, a foreign caterpillar from the Americas, the fall armyworm (FAW) Spodoptera frugiperda is quickly invading the continent, swallowing entire fields of maize, but also sorghum, millets and many other staple crops. There were already armyworms in Africa –worldwide – but the fall armyworm is particularly voracious and versatile, and spreads fast. Targeting over 80 crop species, the caterpillar eats day and night. It’s life cycle can be as short as 30 days and the adult moth is able to fly 100km a night. It is no surprise then that it has invaded over 30 African countries since it was first reported in Nigeria in early 2016. The pest poses a serious threat to the food and nutrition security of millions of farming households in sub-Saharan Africa. According to CABI, the FAW could potentially cause maize yield losses in a range from 8.3 to 20.6 million tons annually in Africa, worth between 2.5 and 6.2 billion dollars, in the absence of any means of control, in just 12 maize-producing countries. But FAW attacks concern also many other important food crops including sorghum and millets, where damages were reported for example in Ethiopia, Kenya, Malawi, Mali, Niger and Rwanda. So what could be the response to this pest problem that is here to stay?

Chemical or natural ways to control the FAW

Looking at what happens in their native lands in Americas, when caterpillars damage over a quarter of the crop field, systemic pesticides are recommended. Some scientists have noted in the past some excesses which have harmed farmers health and the environment without economic sense, alongside building FAW’s pesticide resistance. Pesticide use may be considered against FAW invasion – plant breeders on ICRISAT research stations used it this summer to protect their experiments – but most of the chemicals that control FAW are not tested and registered in most African countries. Therefore, there is a need to evaluate and fast track registration of effective chemicals for the control FAW. This chemical response is however expensive and often out of reach of most smallholders, and will certainly not be used for their staple food like sorghum and millet.

Natural ways to combat FAW can be an efficient and appropriate approach. Biological control, ie the use of natural enemies of a pest, is a successful approach for many devastating insects like pearl millet head borer which can be almost eradicated by parasitic wasps. FAW has several enemies (predators, parasitoids and pathogens) in its native continent but they may be different than the enemies of the local armyworms species. It is advised to list an inventory of possible natural enemies present in Africa, focusing on parasitoid Telenomus wasps, which control quite well the population of FAW in the Americas. About 11 Telenomus species parasitizing many Lepidoptera insects in Africa could be tested for effectiveness against FAW. If no indigenous biological control is effective, some parasitoids could be introduced from the Americas after careful pre-release studies. After defining the effective biological control methods, local production of parasitoids should be set up. This could however take years.

Biological pesticides such as the spray application of Bacillus thuringiensis or nuclear polyhedrosis virus (NPVSf) have shown good results against FAW and could be tested in the context of African farms. However, this solution could be out of reach for most small farmers.

Plants also have the extraordinary capacity to repel or attract insects by emitting specific volatiles. Some “call” caterpillar enemies, such as wasp parasitoids, when the caterpillar starts feeding on the plant. Other plants repel – like the tropical forage legume Desmodium – or attract FAW. A push-pull strategy using Desmodium as intercrop and Brachiaria another forage crop as border can reduce by more than 80% FAW damage as this recent study from the International Center of Insect Physiology and Ecology (ICIPE) shows. Such habitat management approaches including crop rotations, intercropping with compatible companion crops and conservation agriculture need to be tested as such options are more manageable for smallholder farmers.

Developing and distributing resistant varieties could be central to an Integrated Pest Management strategy against FAW. ICRISAT has already developed sorghum lines resistant to stem borer (Lepidoptera) that will be evaluated for responses to FAW, working closely with EMBRAPA-Brazil who has in the past screened sorghum germplasm for FAW resistance. Two potential sorghum lines have been identified in the ICRISAT Genebank, which could be useful for breeding for FAW resistance.

Yet, this breeding effort will also take several years to achieve results, and then there will be the “seed systems challenge” of disseminating these improved seeds to farmers.

Providing a rapid response to African smallholder farmers

While FAO and other players are debating big plans to combat FAW, African smallholder farmers need fast responses to save their harvests in the months to come, faster than plant breeding, biopesticides or biological control. If we take a closer look at the insect cycle and impact on the plant, may be it is a change of perspective that is needed.

First we need to know the extent of the problem. Mobile technologies could help map in real-time the exact location of the attacks. With the fast adoption of smartphones across the continent (about 300 million users already), African farmers could access mobile plant diagnosis applications such as Plantix to check if their field is affected by FAW – there are 30 different types of armyworms (Spodoptera genus), some other than the fall species, creating havoc in some Indian States this year due to favorable weather conditions – and report it to the online community. FAW Hot spots mapping could help assess the damages, understand and forecast future outbreaks and plan long-term FAW management.

Farmers may also have to accept limited damages to the adult crop up to a certain level, let’s say 20%, and invest on protecting seedlings with affordable seed treatment, coating seeds with an appropriate pesticide and fertilizer blend that would protect the seedlings to avoid total wipe out of the crop if the caterpillar attacks early. When feeding on seedlings, FAW may eat buds and tipping points, killing the plant.

Seed treatment is far more affordable for small farmers than spraying the field when the crop has matured, and worth the investment. In West Africa, ICRISAT scientists have demonstrated that 2$/ha of millet and sorghum seed treatment with Apron Star could protect seedlings from pests and fungi up to 40 days, improve crop density by a quarter and yields by up to 50%. Training of farmer organizations and the distribution of small packs of seed treatment, could be implemented quite quickly with the right public private partnership.

While the presence of the fall armyworm is now irreversible in Africa, as insects know no borders, there is now a collective international effort to control its damage. The scope and speed of fall armyworm destruction show how African smallholder farming is vulnerable to emerging risks. It is important that varied approaches to tackle this emerging pest are explored, from biological control, biopesticides to pest tolerance crop breeding. But because so many farming families have no other livelihoods and safety nets, research should focus also on delivering scalable and affordable solutions for the next season.

About the authors

Jerome Bossuet