Hope for farmers in war on armyworms

Caroline Adongo on her maize farm in Kisumu that has been attacked by fall armyworms. Photo / NMG 

What you need to know:

  • The technology named Pherogen is pheromone-based, with the chemical used mimicking the scent that female armyworms release to attract males for mating.

A new technology that disrupts mating in fall armyworms to suppress populations promises to be a game-changer in the fight against the ravenous pest.

The technology named Pherogen is pheromone-based, with the chemical used mimicking the scent that female armyworms release to attract males for mating.

“The pheromone saturates the farm and forms a cloud in the maize field that confuses the males. They thus loiter in the field trying to work out where the pheromones are coming from, throwing them off the females who are left to lay infertile eggs incapable of hatching into young ones,” said Samuel Muchemi, the field director at Provivi, a US-based firm that developed the trap. Muchemi said studies done in Kenya since 2019 have shown that the technique is highly successful.

“Application at the beginning of the crop provides season-long control by disrupting the pest’s mating and preventing damaging populations’ build-up.”

The pheromone sachets are installed using a stick on the farm at a spacing of 20 by 20 metres. At least eight sachets are adequate for an acre. It costs between $24(Shs90,000) and $35 (Shs131,250) per acre to use the technology.

Fall armyworm

“The pheromone is active for 90 days and should be installed before the emergence of the first shoots of the plant and left there until harvesting,” according to Muchemi.

Muo Kasina, a principal investigator for the fall armyworm and other maize pests, says they are seeking a scenario where all farmers will be able to use the biological control method as their primary intervention and only integrate chemical pesticides as a secondary measure if the infestation is getting out of control.

“Management of the pest has been challenging because of its rapid proliferation. It can cause up to 100 percent yield loss if left uncontrolled because the insect lays very many eggs ensuring that within a month it has multiple of generations,” said Kasina during a farm visit at Kalro’s farm in, where the trial on the technology is being done. According to him, some farmers have given up on growing maize due to the costs involved in its management.

“We are seeking a solution to reduce the cost of management and reduce overuse of chemical insecticides as it’s not sustainable.”

Metabolising insecticides

Kasina said maize is not very good at metabolising insecticides, thus requires a big pre-harvest interval, which many farmers do not observe.

“With the love for green maize, the interval may not be enough between the last spray and the roasted maize on our streets. And we have to be worried about what this increased use of pesticides on our food systems more so our staple food, is doing to human health,” says Kasina. Kasina said most farmers discover their crops are attacked by armyworms when the pests are at the caterpillar stage which is the most dangerous.  “Farmers need to start managing this insect intelligently, by scouting their maize farms intensively to catch it at the early stages of egg or tiny caterpillar after hatching.”

Cosmas Nzioka, a farmer, said one has to spray their farms nine times from establishment to harvest said to curb fall armyworm attack.

“This made me stop planting maize. I am tired of spraying the crop every week.” Since its discovery in 2017, the pest has become a major challenge to maize farmers, causing losses of about a third of the annual maize production— about a million tonnes. The new technology has been adopted in Mexico, Brazil and Asia.

Wasps to fight fall armyworm

Meanwhile, as farmers ready for a new maize planting season, many of them are hoping that fall armyworms (FAW) will not attack their crops this time round. The pests have ravaged acres of crops in the last two years, heaping losses on farmers, some who are finding pesticides ineffective.

This season, however, things are looking up for farmers when it comes to controlling pests as the International Centre of Insect Physiology and Ecology (Icipe) and its partners work on insect-controlled method to curb the pests. Scientists at Icipe have identified two local varieties of wasps, Trichogramma and Telenomous, which they release in affected maize plantations to search for and lay their eggs on armyworm eggs thus killing them before they reach the larvae stage where they are most destructive to crops. The two wasps act as natural enemies to most caterpillars that harm a wide array of crops, not just maize.

In the field, the armyworm eggs are spherical, green or cream white in colour, turning dark brown before hatching. The eggs that are usually laid in masses of approximately 150-200 are found in two to four layers deep on the surface of the leaf and are covered with a protective layer that takes three to four days to mature depending on the temperature. Up to 2,500 eggs may be laid by each female.

Within a few days, the larvae emerge and starts to feed on the different crops creating pinholes on leaves and easily make its way to the next crop, county or country.

“The developing larvae eats different parts of the host plant creating gaps on the leaf and a moist sawdust like tress near the funnel of the upper leaves. If the larva attacks early in the season, the feeding can kill the growing plant,” explains Dr Tadele Tefera, a principal investigator at Icipe.

Key facts

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).

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