Stem borer (cereals)
Bores into the cereal stem and kills the central shoot — the "dead heart" of young maize, sorghum and millet, and tunnelled, broken stems later.
- Pest type
- Stem-boring caterpillar
- Attacks
- Central shoot & stem
- Worst in
- Early crop; warm season
- Main risk
- Dead heart; stem breakage
Overview
Stem borers are caterpillars of several moth species that tunnel inside the stems of maize, sorghum (jowar), pearl millet (bajra) and sugarcane. The young caterpillar first scrapes the leaves, then bores into the stem and feeds inside, hidden from view.
In a young plant, boring through the base kills the growing central shoot, which dries into a straw-coloured "dead heart" that pulls out easily while the outer leaves stay green — the classic diagnostic. Later in the season the tunnelling weakens the stem so it lodges or breaks, and cobs and earheads fill poorly. Because the caterpillar is inside the stem, early action and resistant varieties matter far more than late spraying.
How to identify it
- A dry, straw-coloured central shoot ("dead heart") that pulls out easily while the outer leaves of a young plant stay green.
- Rows of small "shot holes" across leaves that unfurl from a bored whorl, and bore holes in the stem with pellet-like frass around them.
- Splitting an affected stem reveals a tunnel and a caterpillar inside.
- Later, broken or lodged stems and poorly-filled cobs/earheads.
The damage it does
- Dead heart that kills the main shoot of young plants, thinning the stand.
- Tunnelled stems that lodge and break, and disrupted movement of water and food to the grain.
- Poorly filled cobs and earheads, and entry points for stalk rots.
- In sugarcane, bored internodes and reduced cane weight and sugar.
When to act
- Scout from early vegetative growth for dead hearts and leaf shot-holes; the young-larva stage is the only time to reach the pest before it is deep in the stem.
- Remove and destroy dead-heart plants as you find them to take out the caterpillars inside.
- Pheromone traps and thresholds for the specific borer help time any spray to egg-hatch.
Organic & cultural control
- Grow resistant/tolerant varieties and sow at the recommended time to escape peak borer activity.
- Release Trichogramma egg parasitoids at the recommended rate, and conserve natural enemies.
- Pull out and destroy dead-heart plants and, after harvest, destroy or deep-plough stubble where borers overwinter.
- Apply Bt or spray/place biologicals against young larvae in the whorl before they bore in.
Chemical control
- Target young larvae in the whorl before they enter the stem — CIB&RC-registered options include chlorantraniliprole 18.5% SC and other registered granular/whorl treatments for the crop.
- Whorl application (granules or a directed spray into the funnel) reaches the borer far better than a general foliar spray.
- Rotate insecticide groups and observe the label pre-harvest interval.
- Confirm the current recommendation and dose for your crop and zone with your local KVK.
Crops most at risk
Where this problem is called out in our crop guides — open a crop for the full package of practices.
Frequently asked questions
The central shoot of my young maize is dry and pulls out easily. What is it?
That is "dead heart" — the classic sign of stem borer. The caterpillar bores into the base and kills the growing central shoot, which dries to straw colour and pulls out while the outer leaves stay green. Remove and destroy dead-heart plants, and target young larvae in the whorl before they get deep into the stem.
Why does spraying often fail against stem borer?
Because once the caterpillar is inside the stem it is protected from any surface spray. Control depends on hitting it early — young larvae still feeding in the whorl — with whorl-directed treatment, plus resistant varieties, Trichogramma releases, and destroying dead-heart plants and stubble. Late foliar sprays largely miss the pest.
How do I reduce stem borer next season?
Sow resistant varieties at the recommended time, destroy or deep-plough crop stubble after harvest to kill overwintering borers, remove dead-heart plants during the season, and use Trichogramma and whorl-targeted treatment against young larvae. These together cut the carry-over and the in-season damage.
Symptoms and control measures follow ICAR, KVK and state agricultural-university package-of-practices; any named chemical is a registered use. Always read the product label and confirm the dose for your crop and zone. editorial policy.