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used, the impact of fall armyworm on maize yields was negligible, according to a 2022 Journal of
Economic Entomology study.
“In almost all fields, the levels of damage [to yields] were sufficiently low that they could be ignored
by the farmers,” said study author Rhett Harrison, a landscape ecologist at CIFOR-ICRAF, which has
headquarters in Kenya and Indonesia.
Harrison said some of the earlier assessments of crop losses relied on self-reporting by farmers.
Because the fall armyworm was new, and the sight of a field full of shredded leaves is alarming ?
especially compared to the less visible damage wrought by common pests like stem borers ? farmers
may have overestimated the problem. Maize is a hardy crop; even very extensive leaf damage by fall
armyworm only results in a slight yield loss, according to another study in PLOS ONE.
It’s also likely that the kind of severe outbreaks seen early on declined as bats, wasps and other
native predators became better at targeting fall armyworms. This is a natural process: initially, an
invasive pest runs amok, but once resident predators realize there’s a new, and plentiful, source of
food around, they start to eat the pest more intensively, potentially keeping its population in check.
Ironically, the knee-jerk reaction of applying highly toxic pesticides can actually interrupt this natural
process. “Often the impact [of these pesticides] on natural enemies is much worse than the impact on
the pest itself,” Harrison said. “Especially with a pest like fall armyworm because of its behavior of
hiding in the whorl, a lot of the individuals don’t actually get hit by a contact pesticide. It’s a kind of
self-defeating exercise.”
That’s where integrated pest management, grounded in the principles of agroecology, comes in.
Farmers can help control outbreaks by making sure there’s habitat for natural predators, for example
by conserving patches of native vegetation and using mulch, according to the CIFOR-ICRAF guide and
other experts. Healthy maize is also more resilient; farmers can use agroecological practices such as
applying compost or manure and intercropping to increase soil fertility. “When the soil is fertile, [the
plant] has nutrients … [it] can resist and recover from an infestation,” said Ivan Rwomushana, a senior
scientist in invasive species management at the U.K.-based Centre for Agriculture and Bioscience
International (CABI), an organization also working on helping farmers manage fall armyworm
There are also a slew of low-cost but labor-intensive fall armyworm control options such as picking
the caterpillars off leaves, putting soil inside the maize whorl to irritate the caterpillar, even filling the
whorl with fish soup to attract natural predators, among others. However, fall armyworm outbreaks can
become more severe in some areas or years, experts say. For example, one risk factor is the
cultivation of irrigated winter maize, which allows fall armyworm populations to build up year-round.
Outbreaks also tend to be worse when the rains aren’t steady; rain can wash away or drown the
caterpillars, and plants aren’t as healthy in drier years and so can’t recover from damage as easily.
If the problem is getting out of hand, farmers can resort to sprays from extracts of neem (Azadirachta
indica) and other plants, which serve as a repellent and can sometimes be more effective than
synthetic pesticides, according to a 2019 Insects study.
There’s also been progress with biological control agents based on viruses, fungi or parasitoids. These
include a baculovirus biopesticide called Fawligen, which was recently licensed in Kenya. Rwomushana
said the benefit of this virus-based pesticide is that farmers can buy and apply the product at the
beginning of the infestation. Then, by collecting the dead caterpillars and crushing them up with
water, farmers can make their own low-cost, virus-laden spray. The virus specifically infects fall
armyworm, so it doesn’t pose a wider risk.
And while fall armyworm is a serious problem that shouldn’t be ignored, it’s not the only problem.
“The investment in these smallholder farmers should be on improving their farming systems and
getting their yields up,” Harrison said. “And this pest is part of the system but it’s not the main
problem in the system.”
- 79 -
Economic Entomology study.
“In almost all fields, the levels of damage [to yields] were sufficiently low that they could be ignored
by the farmers,” said study author Rhett Harrison, a landscape ecologist at CIFOR-ICRAF, which has
headquarters in Kenya and Indonesia.
Harrison said some of the earlier assessments of crop losses relied on self-reporting by farmers.
Because the fall armyworm was new, and the sight of a field full of shredded leaves is alarming ?
especially compared to the less visible damage wrought by common pests like stem borers ? farmers
may have overestimated the problem. Maize is a hardy crop; even very extensive leaf damage by fall
armyworm only results in a slight yield loss, according to another study in PLOS ONE.
It’s also likely that the kind of severe outbreaks seen early on declined as bats, wasps and other
native predators became better at targeting fall armyworms. This is a natural process: initially, an
invasive pest runs amok, but once resident predators realize there’s a new, and plentiful, source of
food around, they start to eat the pest more intensively, potentially keeping its population in check.
Ironically, the knee-jerk reaction of applying highly toxic pesticides can actually interrupt this natural
process. “Often the impact [of these pesticides] on natural enemies is much worse than the impact on
the pest itself,” Harrison said. “Especially with a pest like fall armyworm because of its behavior of
hiding in the whorl, a lot of the individuals don’t actually get hit by a contact pesticide. It’s a kind of
self-defeating exercise.”
That’s where integrated pest management, grounded in the principles of agroecology, comes in.
Farmers can help control outbreaks by making sure there’s habitat for natural predators, for example
by conserving patches of native vegetation and using mulch, according to the CIFOR-ICRAF guide and
other experts. Healthy maize is also more resilient; farmers can use agroecological practices such as
applying compost or manure and intercropping to increase soil fertility. “When the soil is fertile, [the
plant] has nutrients … [it] can resist and recover from an infestation,” said Ivan Rwomushana, a senior
scientist in invasive species management at the U.K.-based Centre for Agriculture and Bioscience
International (CABI), an organization also working on helping farmers manage fall armyworm
There are also a slew of low-cost but labor-intensive fall armyworm control options such as picking
the caterpillars off leaves, putting soil inside the maize whorl to irritate the caterpillar, even filling the
whorl with fish soup to attract natural predators, among others. However, fall armyworm outbreaks can
become more severe in some areas or years, experts say. For example, one risk factor is the
cultivation of irrigated winter maize, which allows fall armyworm populations to build up year-round.
Outbreaks also tend to be worse when the rains aren’t steady; rain can wash away or drown the
caterpillars, and plants aren’t as healthy in drier years and so can’t recover from damage as easily.
If the problem is getting out of hand, farmers can resort to sprays from extracts of neem (Azadirachta
indica) and other plants, which serve as a repellent and can sometimes be more effective than
synthetic pesticides, according to a 2019 Insects study.
There’s also been progress with biological control agents based on viruses, fungi or parasitoids. These
include a baculovirus biopesticide called Fawligen, which was recently licensed in Kenya. Rwomushana
said the benefit of this virus-based pesticide is that farmers can buy and apply the product at the
beginning of the infestation. Then, by collecting the dead caterpillars and crushing them up with
water, farmers can make their own low-cost, virus-laden spray. The virus specifically infects fall
armyworm, so it doesn’t pose a wider risk.
And while fall armyworm is a serious problem that shouldn’t be ignored, it’s not the only problem.
“The investment in these smallholder farmers should be on improving their farming systems and
getting their yields up,” Harrison said. “And this pest is part of the system but it’s not the main
problem in the system.”
- 79 -
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