Divisi
Cereal stem borers
· Insect
Photo: சிகி பாரதி · CC BY-SA 4.0
Cereal stem borers are the caterpillars (grubs) of several dull, brown, night-flying moths — the spotted stem borer, the African maize stalk borer and the pink borer among them — that attack maize, sorghum, millet, rice and sugarcane. The young grubs hatch on the leaves and feed hidden inside the whorl (the funnel of new leaves at the plant's centre), cutting the neat rows of holes you later see marching across the opened leaf; then they tunnel down into the stem, choking off the plant's water and food, killing the growing point and hollowing out the stalk until it snaps. They ride out the dry season as grubs sealed inside old stalks and stubble, so a field left uncleaned after harvest quietly plants next year's attack.
Paul-andre Calatayud · CC BY-SA 3.0 
LEMAUX Yves · CC BY-SA 4.0
Why it matters
In a bad year, stem borers can take up to half your grain (50%). Once a grub tunnels deep inside the stem, no spray can follow it, and when it kills the plant's growing point — leaving a dead centre shoot called a dead-heart — that plant will never make a cob. Worse, the grubs survive the dry season hidden inside old stalks and stubble, so if you leave last season's residue lying in the field they come back stronger the next year. That is why catching them early and cleaning up after harvest beat any spray.
When to act
Around 5 to 10 percent of plants showing fresh leaf shot-holes or early dead-hearts; scout weekly during vegetative growth.
This guidance is general, compiled from published agronomic references including FAO and CABI. Thresholds and timing shift with your crop, your variety and the season.
In much of the region a spray is simply called mushonga — medicine. But a chemical group you cannot name is one you cannot rotate, and a product you did not write down has no pre-harvest interval you can observe. Mushonga, and other farming words →
The full cereal stem borers field guide
- Identify it
- Scout for it
- Control it
16 field-guide sections in the app
The full guide to cereal stem borers — every symptom to check, how and when to walk your field looking for it, and the controls that actually work, ranked. Built into your crop plan, so you are told to look before it costs you a harvest.
Crops it affects
Frequently asked questions
How do I identify cereal stem borers?
The first sign — neat rows of little holes. While the grub feeds on the tightly-rolled young leaves down inside the whorl (the funnel of new leaves at the plant's centre), it punches through all the folds at once. When that leaf later opens out, you see a tidy, straight row of small holes — shot-holes — marching across the leaf, as if someone pushed a pin through folded paper. Neat rows, not ragged tears, are the giveaway.
When should I take action against cereal stem borers?
Around 5 to 10 percent of plants showing fresh leaf shot-holes or early dead-hearts; scout weekly during vegetative growth.
How do I control cereal stem borers?
Prevent — plant early and all together. Sow early and at the same time as your neighbours so the whole area grows past the tender stage before borer moths build up; the late or lonely field is the one they hammer. Keep the crop well-fed and weed-free so it grows fast and can shrug off light damage.
Which crops does cereal stem borers affect?
Among the crops covered here: Maize, Pearl millet, Rice, Sorghum, Sugarcane.
Catch it before it costs you a harvest
Divisi builds scouting into your crop plan — it tells you when to walk your field, what to look for at that stage, and what to do when you find it. Free for farmers, works offline.
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