How to Control Fall Armyworm in Maize Without Synthetic Insecticides

3 hours ago

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TL;DR: Fall armyworm is easiest to control while the caterpillars are small, in the first four to five weeks after maize comes up. Walk the field twice a week, spray only when about one plant in five shows fresh damage, aim the spray into the whorl in the early morning or evening, and repeat every 14 days while damage continues. A plant-based insecticide such as Conqueror, mixed at 120 ml per 16-litre knapsack, fits this plan.

Young maize plant with water droplets on its leaves, the stage when fall armyworm attacks the whorl

What is fall armyworm?

Fall armyworm (Spodoptera frugiperda) is a moth whose caterpillars feed on more than 80 crops, but prefer maize. It came from the Americas and was first found in Africa in early 2016, in Nigeria, Benin, São Tomé and Togo. Within two years it had spread across most of sub-Saharan Africa.

The caterpillar does the damage. It hides deep in the funnel of young leaves (the whorl), feeds at night, and moves into the cob as the plant matures. A University of Benin study (2023) describes it as capable of destroying a maize crop completely when it isn't controlled.

How to recognise it

On the leaves: small, see-through "windows" on young leaves at first, then ragged holes and torn edges.
In the whorl: wet sawdust-like droppings (frass) packed into the funnel.
On the caterpillar: a pale upside-down "Y" on the head, and four dark spots in a square near the tail end.
In the cob: holes in the husk and chewed grain at the tip.

Why timing matters more than the product

Young caterpillars (the first few days after hatching) are small, feed on the leaf surface and die easily. Older caterpillars burrow deep in the whorl or the cob, where no spray reaches them well. That's true for synthetic insecticides as well as plant-based ones.

The most effective way to control fall armyworm in maize is to find it early and spray while the caterpillars are small. CIMMYT's guide to fall armyworm management in Africa recommends regular scouting and suggests acting when about 20% of plants show fresh damage at the early whorl stage, and about 40% at the late whorl stage. Spraying earlier than that wastes money, and spraying later means the caterpillars are already too big and too well hidden. Spray into the whorl, where the caterpillars feed, in the early morning or late evening when they're active and the spray doesn't dry too fast. Repeat at the interval on the label while new damage keeps appearing. Plant-based insecticides work best on young caterpillars, so field trials in Nigeria have found neem-based treatments reduce damage and improve yields when they're applied early.

How to control fall armyworm, step by step

1. Scout twice a week from emergence

From the day maize comes up until tasselling, walk the field twice a week. Check 10 plants in each of 5 spots, following a "W" path across the field. Count how many of the 50 plants show fresh damage (wet frass, new windows, live caterpillars). Old, dry damage doesn't count.

Crop stage	Spray when fresh damage reaches
Early whorl (about 2–4 weeks after emergence)	about 10 of every 50 plants (20%)
Late whorl (about 4–7 weeks)	about 20 of every 50 plants (40%)
Tasselling and cob	Check the cobs. Spraying is less effective now

Source: CIMMYT, Fall Armyworm in Africa: A Guide for Integrated Pest Management (2018). These are guideline figures, not rules. Act sooner if the field was badly hit last season.

2. Use cultural controls alongside spraying

Plant early and at the same time as your neighbours. Late-planted fields get the largest moth populations.
Keep the field weeded, especially the edges where moths lay eggs on grasses.
Crush egg masses and young caterpillars on small plots. Egg masses are cream-coloured clusters covered in fine hairs on the leaf.
Intercrop maize with beans or cowpea where you can.
Feed the soil. Strong, well-fed maize recovers from leaf damage faster. See What Is Biochar Fertilizer?

3. Mix and spray correctly

For Conqueror, Vertex Agro's organic insecticide:

Shake the bottle well.
Half-fill a 16-litre knapsack with clean water.
Add 120 ml of Conqueror, mix, then top up with water.
Spray straight away, aiming the nozzle down into the whorl of each plant.

Crop	Pests on the label	Rate per hectare	Knapsacks per hectare	Repeat every
Maize, sorghum	Armyworms, budworms, cutworms, bollworms	800–900 ml	about 7–8	14 days
Beans, soybeans, peas	Bean weevils, bollworms, armyworms	800–900 ml	about 7–8	14 days

First spray: 2–3 weeks after the crop comes up, or as soon as scouting shows damage above the threshold.

Last spray before harvest: check the label for the number of days to wait between the last spray and harvest.

4. Check the result

Go back 3–4 days after spraying. Caterpillars that have fed on a plant-based insecticide often stop feeding before they die, so look for new damage rather than dead caterpillars. If fresh damage is still rising, respray at the label interval.

Do plant-based insecticides work on fall armyworm?

Yes, when they're used early. The evidence from Nigerian research is encouraging:

Study	Treatment	Finding
Gombe State field trials, 2021–2022	Neem leaf extract, 20%	Controlled fall armyworm on maize about as well as the synthetic standard used for comparison
Abuja field study, 2018	Neem oil	Second most effective treatment after a synthetic pyrethroid
University of Benin, 2023	Fresh neem leaves used as mulch	Grain yields rose 410–600%, partly from pest control and partly from better soil fertility

Plant-based products don't knock pests down as fast as some synthetics. Their strength is that they work in more than one way: they kill on contact and when eaten, stop caterpillars growing and moulting, and put adult moths off laying eggs. Conqueror combines plant extracts, so it works in each of these ways. It's registered with NAFDAC (A5-2334).

Common mistakes

Spraying too late. Once caterpillars are in the cob, no spray works well. Scout from week one.
Spraying in the midday sun. The spray dries before it reaches the whorl, and caterpillars are hiding. Spray early morning or late evening.
Covering leaves but missing the whorl. Point the nozzle into the funnel.
Using less water than the label says. It can scorch the crop and gives poor coverage.
Treating "plant-based" as harmless. It's still a poison. Wear gloves and a face mask, and keep it away from children, food, drinking water, streams and ponds. Spraying early or late also avoids the hours when bees are feeding.

Frequently asked questions

How do I know if my maize has fall armyworm?

Look for see-through windows on young leaves, ragged holes, and wet sawdust-like droppings in the whorl. The caterpillar has a pale upside-down "Y" on its head and four dark spots in a square near its tail.

When is the best time to spray for fall armyworm?

Early morning or late evening, when caterpillars are feeding and the spray won't dry too fast. Spray when about 20% of young plants show fresh damage, aiming into the whorl.

How much organic insecticide do I mix in a knapsack for armyworm?

For Conqueror, mix 120 ml in a 16-litre knapsack. That's about 7–8 knapsacks, or 800–900 ml, per hectare of maize. Repeat every 14 days while new damage appears.

Can neem kill fall armyworm?

Neem reduces fall armyworm damage, especially on young caterpillars. Nigerian field trials in Gombe and Abuja found neem extract and neem oil among the most effective treatments tested, though results vary with dose and timing.

Why is fall armyworm still eating my maize after I sprayed?

The caterpillars were probably too big, hidden in the whorl or cob, or the spray missed the whorl. Plant-based insecticides also stop feeding before caterpillars die. Check for fresh damage 3–4 days later and respray at the label interval.

Protect your maize this season

Fall armyworm is beatable when you catch it early. Scout twice a week, spray into the whorl when damage passes the threshold, and keep going at 14-day intervals.

Not sure how much you need? Tell us your crop, your farm size and what you're seeing in the field. We'll tell you which product to use and where to buy it near you.

Call +234 803 618 6987 · See Conqueror →

Sources

Goergen et al. (2016), First Report of Outbreaks of the Fall Armyworm in West and Central Africa, PLoS ONE
Prasanna et al. (eds.) (2018), Fall Armyworm in Africa: A Guide for Integrated Pest Management, CIMMYT
University of Benin neem-mulch study (2023): IITA repository
Gombe neem extract trials (2021–22): AJOL
Abuja neem oil study (2018): Nigerian Agricultural Journal