How to win the war against armyworm without pesticides

Janet Odiyo's maize farm that is buffered by napier grass. She has had bumper harvests from using the push-and-pull technology. PHOTO | COURTESY

What you need to know:

  • After carefully studying the pest and testing the desmodium and Napier grass strategy, Icipe announced a breakthrough last November.
  • They collected data and samples, which they tested in the laboratory, and found that intercropping with desmodium and planting Napier grass along the farm border, keeps fall armyworms away from crops.

Two decades ago, farmers in the Lake Victoria Basin were at wits’ end.

They had suffered untold suffering and losses in harvests thanks to the parasitic weed striga, and the stem borer.

As farmers counted their losses, scientists from the Nairobi-based International Centre of Insect Physiology and Ecology (Icipe), brought out their thinking caps, with the aim of finding a solution that would end the farmers’ suffering.


In the team was Prof Zeyaur Khan, who is now the principal scientist and leader of the Habitat Management Programme at the Centre.

While researching different types of grasses, they chanced upon desmodium, a large perennial tropical forage legume, which suppressed the destructive striga weed.

“We could not believe what we had found. We repeated our research several times in our laboratories, until we proved it would work,” he recalls.

The farmers, who had faced uninspiring harvests for many years, gladly embraced the solution, which offered more than one benefit.

Besides repelling striga and pulling stem borers from crops, desmodium also improved soil fertility and reduced erosion, and could also be used as fodder for livestock.

By 1998, after Icipe scientists had introduced desmodium as a parasite control strategy, more than 2,000 farmers had started intercropping their food crops with desmodium and bordering their farms with Napier grass.

Fast-forward to 2016, when the fall armyworm made its entrance, catching farmers by surprise.

One of those farmers was Rose Otieno, the secretary of the 15-member Ayieko Women Group in Lambwe Valley.

She knew that using desmodium controls striga weed, but she had no idea that it could also manage the fall armyworm.

She watched as the pest destroyed her entire maize crop and left her with devastating losses.

The pest left farmers terrified by its destruction and the fact that it did not respond to pesticides.

They formed groups to put their heads together and put up a united front against the armyworm, to no avail.

A maize crop attacked by fall armyworm at Ngeria Farm Prisons in Uasin Gishu County on April 24, 2018. PHOTO | FILE


Then Icipe came to their rescue, with what they called the push and pull technology.

It began with a phone call from Kitale, in Kenya’s maize belt, where farmers were also counting their losses, after the dreaded caterpillar ravaged acres of crop. Lillian Gumbe, called Prof Khan at Icipe, after many years of silence.

“We talked about the fall armyworm and the destruction it was causing on maize farms. I imagined she would be among the affected, but she told me that while every other farmer was experiencing huge losses, her crop had not been attacked. The difference between her farm and other farms, was that she grew desmodium, a pest repellent plant,” he recalls.

Prof Khan and his team went to Kitale, where they last worked with farmers in 1997.

They collected data and samples, which they tested in the laboratory, and found that intercropping with desmodium and planting Napier grass along the farm border, keeps fall armyworms away from crops.

After carefully studying the pest and testing the desmodium and Napier grass strategy, Icipe announced a breakthrough last November, by which time farmers from 43 out of 47 counties were in tears from trying to win the war against the stubborn parasite.

Between April and May 2017 alone, 250,000 hectares of maize crop in Kenya had been attacked by the destructive worm.

Rose Otieno and her friends from the Ayieko Women Group in Lambwe Valley, were among the farmers counting their losses, but that was before Icipe introduced them to the aptly named push and pull technology.

According to Prof Zeyaur Khan, the push and pull technology involves intercropping cereals with a pest repellent plant such as desmodium, which drives away stem borers and fall armyworm from the food crop.

To make it more effective, Napier grass is planted around the border of the intercropped cereal plants, to attract and trap the pests, thereby keeping them away from the food crop.

The technology has proved successful in managing the pest that has ravaged staple crops like maize, worsening food insecurity in Kenya, East Africa and the wider sub-Saharan Africa.

“We are optimistic that we will have a bumper harvest from our farms this time round. We have planted desmodium and Napier grass to manage the pest,” says a triumphant Ms Otieno.


Samwel Oyoo, another farmer, and the chairman of Nyasanja Youth Group in Lambwe Valley in Homa Bay County, has also learnt that he can use desmodium for more than dealing with the striga weed, which had invaded his farm. Now he uses it to keep out the fall armyworm as well.

“Last year’s maize harvest was poor. That is why we embraced the push and pull technology after being trained by scientists from Icipe,” says Mr Oyoo.

Already, he can see the difference between his crops, and those of other farmers who are not applying the push-pull technology.

Untouched by pests, his look way healthier and stand out from the rest.

His friends at the Nyasanja Youth Group have also embraced the technology, and reaped increased acreage under healthy maize for their efforts.

Other farmers were in on the secret, way before the pest became a nuisance.

“Last year many farms were attacked by the fall armyworm, but my crops were left untouched, thanks to the push and pull technology,” says Reuben Onyango, a maize farmer who has used push and pull as a pest control strategy in Kanyada, Homa Bay, for the last four years.

Mr Onyango, a retired teacher, says the push and pull technology gives him 50 times more yield than on another farm where he does not practise the technology.

He uses desmodium and mulato, not just to repel pests, but also to fertilise his crops, then as fodder for his cows.

“I do not have pest infestation on my farm, unlike in other farms where push and pull is not practised,” he says, noting that many farmers stopped growing maize and sorghum due to the pest.

But having seen the wonders the push and pull technology is doing on his farm, they are now ditching the sweet potato vines they turned to, and going back to growing the cereals they surrendered to the fall armyworm. Now push and pull keeps the pests away.

“To make maximum profit from agriculture, farmers need to adopt the technology,” Mr Onyango says.

Janet Odiyo, from Lambwe Valley in Homa Bay County, has been using the push and pull technology as a pest control strategy for the last seven years. She says that it is the most sustainable way to go for serious farming ventures.

The 67-year-old farmer says that she has been recording bumper harvest in all the years she has intercropped with desmodium and Napier grass.

“It is unfortunate that some people within my area have not adopted the technology despite seeing how my harvest has grown over the years,’ she said at an interview on her farm.


Following the outbreak and spread of fall armyworm in 2016 to date, many farmers are now adopting push and pull technology as it helps reduce the pest infestation that had caused crop loss.

The Fall armyworm (Spodoptera frugiperda) which destroys crops especially maize, flies nearly 1,600 kilometres in just 30 hours and has already migrated across Africa reaching 50 of the 54 nations since 2016 when the voracious pest native to tropical and subtropical America first appeared in West Africa, according to United Nations Food and Agriculture Organisation (FAO). By 2017 it had reached parts of eastern, southern and northern Africa.

The pest spreads fast because one female moth lays 1,500 to 2,000 eggs in three weeks. The larvae feed on 100 plant species including maize, rice, sorghum, millet, sugarcane, vegetables and cotton.

They devour leaf whorls, ears and tassels of maize crops, resulting in zero yield.

These food crops are staple foods in Africa, thus destruction by pests points towards a dire food insecurity situation, if the pest is not effectively and sustainably controlled.

Last year, FAO warned that the pest will persist and cause serious damage to key crops that provide nutrition and support the livelihoods of many subsistence farmers.

Although the vicious pest can be managed using some synthetic pesticides, few African nations have come up with successful application methods for these chemicals.

Moreover, this method means additional expenses to poor farmers, who also have to be trained on the appropriate use of the poisonous chemicals. Icipe developed the push-pull technology for the control of the cereal stem borers, but it is now an added innovation for the management of the fall armyworm.

The technology involves intercropping maize with Greenleaf desmodium (Desmodium intortum) and planting Brachiaria or Napier grass as a border crop.

Desmodium offers protection by emitting substances known as semiochemicals, which repel (push) stem borer moths and fall armyworms. Then semiochemicals released by the border crop Brachiaria attracts (pulls) the pests away from the crops.

Scientists from Icipe and Rothamsted Research in the UK, also conducted research with 250 farmers who had adopted the technology in drier areas of Kenya, Uganda and Tanzania.

Each farmer had a set of two plots: one was a climate-adapted plot using the push-pull intercropping technology, while the other was a maize monocrop (just one crop planted) plot.

They found that in the climate-adapted push-pull plot, there was an 83 per cent reduction in the average number of larvae per plant and an 87 per cent reduction in plant damage, than in the maize monocrop plot.

Similarly, maize grain yields were significantly higher (almost threefold) in the climate-adapted push-pull plots.


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Cereal farmers across sub-Saharan Africa are experiencing heavy losses due to the devastation by the Fall army worm. It has caused huge losses, especially of maize and sorghum, affecting food security and trade.

The fall armyworm’s lifespan, from egg to larva to moth, lasts between one to three months. It’s during the larva stage that it does the most crop damage. Controlling them is a challenge because they reproduce fast and in large numbers, can migrate great distances, hide within growing leaves and have been reported to resist several pesticides. Emergency responses by the affected countries have been based on the use of pesticides, but in most cases this has proven costly and not very effective.

Various tactics – both old and new – are being tested to try and control the fall army worm in Africa. These include the use of inter-cropping technology, natural enemies, early warning systems and use of biopesticides.

To combat the voracious pest, and prevent the huge losses, policymakers, extension agencies and growers could learn from the experiences of farmers in the Americas, and adapt the same to suit the smallholder African production system. This knowledge must be shared with farmers and agricultural officers.

The pest, an alien from the Americas, was first reported in Africa in 2016. Starting in the São Tomé and Príncipe islands and Nigeria, in just two years it spread to over 38 African countries.

The speed with which they spread could be due to a few factors. Firstly, female armyworms produce a huge number of eggs (between 50 - 200 eggs per batch), and can have up to 10 batches within her lifespan. Secondly, the moths are carried by the wind across vast distances. Some have been known to travel up to 1,000km. Thirdly, numbers aren’t being reduced by their natural enemies which means they can multiply uninhibited.

All these factors are crucial to keep in mind when managing an outbreak.

Pesticides: The use of chemical pesticides seems to be most common practice that is currently heavily supported by government. But pesticides can be harmful, particularly to the environment as they affect non-targeted organisms, like bees. Though often overlooked, there are other, more natural approaches which have proven effective.

Push-pull and other intercropping technology: In this approach crops are grown alongside one another. Some act as a deterrent to insect pests and weeds. The system has reduced pest infestation drastically. This technology has the additional benefit of providing high quality fodder for livestock and improving yields and soil fertility.

For example, when a “trap” crop (such as napier grass) is planted around maize rows, it attracts stemborer moths to lay eggs on it. But, because the grass isn’t nutritious, very few stem borer larvae will survive. In the case of fall armyworm, this has proven effective when maize is inter-cropped with drought-tolerant greenleaf desmodium and planting Brachiaria as a border crop around this intercrop. On the basis of these multiple benefits the International Centre of Insect Physiology and Ecology and partners are rolling out the approach in sub-Saharan Africa.

Early warning, surveillance and monitoring systems: Surveillance and monitoring are crucial to managing an outbreak. They ensure that identification happens very early, before a full outbreak, and allows for proper response management.

Pheromone traps, which use the smell of a female armyworm to attract a male, can be a useful surveillance tool. Judging by the number of moths captured, an infestation can be quickly recognised. These types of surveillance systems are already being demonstrated within some communities. The traps can also be used for mass trappings to reduce the numbers.

Biocontrol: several ecologically sustainable biocontrol solutions are available to farmers. The release of natural enemies is one of them. Parasitic wasps for example can provide (up to 70 per cent) control for fall armyworm by laying their eggs on or inside the fall armyworm eggs or larvae.

Scientists at International Centre of Insect Physiology and Ecology have also identified locally available natural enemies, such as the wasp Cotesia icipe, which has proven effective against the armyworm larvae in the lab.

If these natural enemies are reared in bulk, they can be released in huge numbers in affected fields and conserved. As they multiply in the fields, they can control the pest as they feed on the pest’s larvae.

Biopesticides: These are a fungal, viral or bacterial based product which kill the fall army worm. Examples include the fungi-like Metarhizium anisopliae or bacteria-based Bacillus thuringiensis that have proven effective against fall armyworm and have been used to control it in the US and Brazil.

There are also botanical pesticides which act as both deterrent and toxins. These can prevent the caterpillar from feeding on the crop but also interfere with its ability to grow.

Efforts to control fall armyworm by African governments could draw on the lessons of all these interventions which have been used in the Americas but also trialled in Africa. Obviously, local adaptations will need to be made. But the Fall army worm will remain in Africa for a long time unless concerted action is taken, drawing on the various methods from America and those available in Africa.


Saliou Niassy is the head of technology transfer unit, while Sevgan Subramanian is an entomologist and insect pathologist, at Icipe. This piece was first published by The Conversation.


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