The maize came up evenly with the short rains, and for two weeks it looked perfect. Then one morning the young leaves are covered in small papery windows, a few plants have ragged holes, and down in the funnel of the plant there is a little heap of what looks like wet sawdust. The fall armyworm has arrived. By the time the damage is obvious from the path, the caterpillars inside the whorls are already larger, harder to kill and eating faster every day.
Fall armyworm (Spodoptera frugiperda) is a moth native to the Americas that was first reported in Africa in 2016 and in Kenya the following year. It has since become a regular pest of maize across the country, in both rainy seasons. Its caterpillars feed mainly inside the whorl, the tightly rolled young leaves at the top of the plant, which is exactly the place a casual spray from the path does not reach.
This guide is about the two things a smallholder controls: finding the pest early by scouting properly, and, when control is needed, getting the spray into the whorl where the caterpillars are. Product choice belongs to the label and your extension officer, and we point you there. The equipment, the timing and the technique are what this article is about.
Know What You Are Looking For
Fall armyworm goes through four stages: egg, caterpillar (larva), pupa and moth. The moths fly at night and lay eggs in clusters, usually on the leaves, covered with a layer of fine scales that makes them look furry or fuzzy. The tiny caterpillars that hatch start by scraping the leaf surface, which leaves the translucent windowpane patches that are often the first sign. As they grow they move into the whorl and chew ragged holes through the rolled leaves, so that when those leaves unfold they show rows of holes. Wet, sawdust-like droppings (frass) in the whorl are a strong sign that a caterpillar is inside.
Larger caterpillars have a pale, inverted Y shape on the front of the head and four dark spots arranged in a square on the upper side of the second last body segment. Those two marks help separate fall armyworm from the other caterpillars found on maize. When the caterpillar is fully grown it drops to the soil to pupate, and a new moth emerges to start the cycle again, which is why fields can be reinfested through a season.
Scouting: A Routine, Not a Glance
A walk along the edge of the field tells you very little, because edge plants are not typical and damage is often patchy. A simple routine gives a far better picture in about half an hour on a small farm. Extension programmes in Kenya and the wider region commonly teach a version of the following, and your county extension officer can give you the local recommendation.
Walk the field in a W pattern, starting a few rows in from the edge. Stop at five points spread along the W. At each point, check ten plants in a row, one after another, rather than picking the ones that look damaged. For each plant, look at the newest leaves and down into the whorl for fresh windowpanes, holes, frass or caterpillars, and check the undersides of a couple of leaves for egg masses. Record how many of the fifty plants show fresh damage.
Scout at least once a week from emergence until the maize tassels, and more often if neighbours are reporting damage. Keep the numbers in a notebook. The trend matters as much as the figure: a field that goes from a few damaged plants to many in one week needs attention even if the absolute number is still modest. Note fresh damage specifically. Old windowpanes on lower leaves of a plant whose new leaves are clean may mean the caterpillar has already gone or died, and that plant does not need spraying.
Maize tolerates some leaf damage, especially in the later vegetative stages, and spraying every field at the first hole wastes money and kills natural enemies such as parasitic wasps, earwigs and ants that eat eggs and small caterpillars. This is why action levels exist: they set the point where control costs less than the damage you are preventing. Ask your extension officer for the current recommendation for your area.
Non-Chemical Steps That Help
On small plots, crushing egg masses and picking caterpillars out of whorls by hand during scouting is practical and costs nothing. Planting at the onset of the rains, at the same time as neighbours, avoids a lone late field that attracts moths from everyone else's crop. Healthy, well fed maize grows through damage better than stressed maize, so timely weeding and fertiliser help too.
The push-pull system developed by icipe in Kenya, in which maize is intercropped with desmodium and bordered with Brachiaria grass, has been adapted for fall armyworm and is promoted in several counties. It takes a season or two to establish and suits farmers who also want fodder. Ask your extension office whether seed and support are available locally.
When You Spray, Spray the Whorl
If scouting shows control is needed, the product decision comes first and it is not one to guess. Use only a product registered by the Pest Control Products Board for fall armyworm on maize, which your agrovet or extension officer can confirm, and follow the label for rate, mixing, protective equipment, re-entry interval and the pre-harvest interval if you will eat or sell green maize. Biological products based on naturally occurring organisms are also registered for this pest; they tend to work best on young caterpillars and still need to reach the whorl.
Then comes technique, and this is where most spraying for fall armyworm fails. The caterpillars sit inside the funnel of the plant. A broad, fast pass that wets the outer leaves leaves them untouched. What works is a directed spray: walk slowly along the row, point the lance into the top of each plant, and give each whorl a short burst so the liquid runs down into the funnel. It is slower than blanket spraying, but on young maize it uses less liquid per acre, because you are spraying the target and not the ground between plants.
- Pressure and nozzle. Moderate, steady pressure and a nozzle that gives a narrow, coarse cone or jet put liquid into the whorl rather than drifting as a fine mist. Our guide to spray nozzle selection explains the choices.
- Time of day. Early morning or late afternoon is the usual advice: caterpillars are more active, temperatures are lower and the wind is usually calmer.
- Rain. Do not spray just before heavy rain. The label states how long the product needs to dry; our article on spraying in the rainy season covers rainfastness.
- Calibrate first. Spot spraying still needs a known output per plant so the dose on the label is respected. Our knapsack sprayer calibration guide shows how to measure it with a bucket and a watch.
- Rotate. Repeated use of the same chemical group encourages resistance. Ask your agrovet which groups to alternate.
Spot spraying also changes how much you mix. Because you only treat plants that showed fresh damage in scouting, work out roughly how many plants need treating and mix only what that job needs, following the label concentration. Leftover spray mix is a disposal problem, not a saving. Rinse the tank three times and spray the rinse water over the treated area, as many labels advise, rather than pouring it near a well, stream or the homestead. Never decant products into food or drink bottles, and keep the sprayer itself out of reach of children and animals between jobs.
Late Season: Tassels, Cobs and Green Maize
As maize approaches tasselling, the whorl opens and caterpillars have fewer places to hide, but some move into the developing tassel and later into the cob, where they feed on the silks and grain through the tip or the side of the husk. Damage at this stage is harder to reach with any spray, and on most smallholdings the practical response shifts from spraying to scouting and hand removal. Damaged cobs are also open to moulds once rain gets in, so they are worth separating at harvest rather than mixing with clean grain.
If you grow maize for green cobs, the pre-harvest interval on the label becomes the deciding factor. Some products cannot be used within a set number of days before harvest, and green maize is harvested weeks earlier than dry grain. Check the label before every late spray, and if the interval does not fit, do not spray.
Work With Your Neighbours
Moths fly between farms, so one well managed field next to several unmanaged ones will keep receiving new eggs. Groups that scout on the same days, share what they find with the extension officer and plant at about the same time tend to stay ahead of the pest more easily than farmers working alone. Telling a neighbour that you have found egg masses costs nothing and may save both fields a spray. Many counties also run plant clinics where you can take a damaged leaf or a caterpillar in a closed jar for identification and advice, which is a good habit whenever you are not sure what you are looking at.
Choosing the Right Sprayer for Spot Spraying
For directed spraying, a sprayer that is comfortable to carry and holds steady pressure matters more than a big tank. A manual knapsack sprayer of 16 or 20 litres is the standard choice for half an acre to a few acres. On a manual pump, the pressure drops as you stop pumping, so the dose per whorl varies unless you pump at a steady rhythm. A battery sprayer keeps pressure constant without pumping, which makes it easier to deliver the same short burst into every plant; the trade off is the battery, which needs charging and care. Our guides to knapsack sprayer maintenance and the range of sprayer sizes cover the options.
For a kitchen garden of a few dozen maize plants, a small hand sprayer is enough. Whatever the size, keep a separate sprayer for herbicides so no residue ever reaches the maize, wash the tank and lance after each use, and store products safely; our guide to storing and handling agrochemicals explains how. Wear the protective equipment the label specifies, at a minimum gloves, long sleeves, boots and eye protection, and wash before eating or smoking.
Equipment for Scouting and Spot Spraying, With Prices
These are current prices from the Fuga price list; confirm stock with the team before you travel.
| Item | Stock code | Price |
|---|---|---|
| PREMIER 16LTRS KNAPSACK | 6443 | KSh 1,550 |
| PREMIER 20LTRS KNAPSACK | 6442 | KSh 1,650 |
| KNAPSACK FARMATE 20 LTS - MANUAL | 6285 | KSh 2,200 |
| 16LTR SPRAYER 2 IN 1 | 6470 | KSh 5,000 |
| 16.0 LITRE BATTERY | 6106 | KSh 5,500 |
| 5L PRESSURE PUMP | 6115 | KSh 1,000 |
| 1 Litre Hand Spray | No code | KSh 130 |
| Pressure Sprayer Rods | No code | KSh 350 |
Scout weekly in a W, act on fresh damage while caterpillars are small, use a registered product as the label directs, and put the spray into the whorl one plant at a time. For help choosing between a manual and a battery knapsack, or for nozzles and a spare sprayer lance, talk to any Fuga branch or WhatsApp 0716 961 018. For the weeks before the pest arrives, our guide to planting in the short rains covers seed, spacing and gap filling.
Key Takeaways
- Look for windowpane patches on young leaves, ragged holes and wet sawdust-like frass in the whorl; these are the signs of fall armyworm in maize.
- Scout weekly from emergence to tasselling: walk a W, stop at five points, check ten consecutive plants at each, and record the share with fresh damage.
- Act on fresh damage while caterpillars are small, using the action level your extension officer recommends rather than spraying at the first hole.
- Use only products registered by the Pest Control Products Board for fall armyworm on maize, and follow the label for rate, protective equipment and pre-harvest interval.
- Direct the spray into the whorl of each plant with moderate pressure, early in the morning or late in the afternoon, and calibrate the sprayer first.
- Scout again a few days after spraying, and treat only plants with fresh damage on new leaves.
Frequently Asked Questions
How do I know if my maize has fall armyworm?
Early signs are small translucent windowpane patches on young leaves, followed by ragged holes in the leaves as they unfold and wet, sawdust-like droppings in the whorl. Larger caterpillars have a pale inverted Y on the head and four dark spots in a square near the tail end. Egg masses look like fuzzy clusters on the leaves.
How often should I scout maize for fall armyworm?
At least once a week from emergence until tasselling, and more often if neighbours report damage. Walk the field in a W, check ten plants in a row at each of five points, and record how many show fresh damage. The trend from week to week tells you whether the problem is growing.
When is the best time to spray fall armyworm?
Early morning or late afternoon is the usual advice, when caterpillars are more active, temperatures are lower and the wind is calmer. Spray while caterpillars are young, aim into the whorl of each plant, and avoid spraying just before heavy rain. Follow the product label for timing and intervals.
Which chemical kills fall armyworm?
Several products are registered in Kenya for fall armyworm on maize, including biological options. Product choice should come from the label and your extension officer or agrovet, who can confirm what is registered by the Pest Control Products Board. Rotating between chemical groups helps slow resistance.
Is a battery sprayer better than a manual knapsack for fall armyworm?
Both work. A manual knapsack is cheaper and simple to maintain, but its pressure falls if you stop pumping, so the dose per whorl can vary. A battery sprayer holds steady pressure without pumping, which makes it easier to give each plant the same short burst, but the battery needs charging and care.
