Millet head miner

The clearest and earliest sign is a winding spiral line of cut and missing grain running down the millet head (the candle-shaped grain spike at the top of the plant). Along that track the tiny flowers — the florets, which should each swell into a grain — are eaten away, so the head turns half-empty, chaffy and light in your hand, often with dry droppings caught among the florets.

Peel open an affected head and you'll find one or a few caterpillars the size of your thumbnail up to your first thumb-joint (about 1–2 cm long) — pinkish-brown to greenish, with faint darker bands and a dark head — curled among the florets where they feed. The adult is a small, drab straw-coloured moth that flies only at night, so you will almost never see it: hunt for the caterpillar and its spiral, not the moth.

A head emptied by drought or heat is bare evenly, all over, with no spiral track and no grub. Birds such as quelea strip grain from the outside, leaving ragged, pecked heads — again no spiral and no caterpillar. Grain smut or mould leaves dark, dusty or discoloured grain but keeps the head's normal shape and has no tunnel. Only the head miner leaves that neat spiral of cut florets with a caterpillar still at work inside.

This is the danger window — the night-flying moths lay their eggs exactly as the heads emerge, especially in the days after a good rain. Start checking when the first heads show, and keep going every few days while the heads are still soft and filling.

, not just the edge nearest the path, so you cross all four corners and the middle. Make about 5 stops along the W.

At each stop, check 10 heads (about 50 heads in all). Look closely at the emerging heads, and gently open a few of the softest, newest ones — search among the florets for young caterpillars and for the first sign of a fresh spiral channel.

With only one generation a year and the grub hidden inside, there is no 'wait and see': the moment you confirm it on the emerging heads, move to control and start planning to break the cycle for next season.

Sow with the first good rains, at the same time as your neighbours, so your heads push out and pass the tender stage before the moths are flying in numbers. Late or staggered planting is the head miner's best friend: it keeps offering fresh young heads for the moths to lay on just as their flight peaks.

Where you can, grow a shorter-cycle or less-preferred local millet that heads early and dodges the main moth flight. After harvest, plough or dig the field over to turn up and destroy the resting stage — the pupae sleeping in the soil — so far fewer moths rise on your land next year.

A tiny parasitoid wasp (Habrobracon hebetor — a natural enemy that lays its eggs on the head-miner caterpillars; its young then feed on and kill them) is the most effective control in the Sahel. Farmers release these wasps during heading, usually from simple release bags or stations supplied through extension services or a farmer group — ask your extension officer or group how to get them. Protect the wild ones already living in your field by not spraying broad poisons that would wipe them out.

There is no reliable insecticide for this pest: once the caterpillar is spiralling inside the head, no spray can reach it, and a broad poison only kills the bees and the helper wasps that are on your side. If you are ever tempted to spray anyway, treat it as a true last resort and handle it safely — cover your skin, eyes, nose and mouth; spray in the cool of morning or evening with the wind at your back; keep it well away from food, drinking water, children and beehives; wait the full pre-harvest interval (the set number of days between spraying and harvest so no poison is left on the grain); and wash yourself and your sprayer afterwards. And never spray the same product again and again — rotate between different chemical groups so the pest can't build resistance (stop being killed by a poison that is used too often).

If the heads are already heavily mined and empty, nothing this season will bring the grain back: harvest whatever has filled and cut your losses. Then break the cycle for next year — plough in the stubble to bury the resting pupae, plant early and all together next season, and arrange a wasp release with your neighbours so the whole area heads early and starves the moths at once. Because this pest carries over in the soil and flies in from around you, beating it works best when the whole community acts together.