Angoumois grain moth

kernels with a neat round hole about the size of a pin-head, often capped by a thin, see-through flap or 'window' of grain skin where the moth pushed its way out. Hold a handful up to the light — the bored grains look empty and papery and feel light. Tip the handful into water and the hollow, moth-eaten grains float while the good, solid grain sinks.

when you open the store or pour the grain, small straw-coloured (buff) moths flutter up, most of all at dusk; they settle on the grain, the sacks and the walls. In a heavy attack the grain feels warm to your hand, smells musty or mouldy, and carries patches of fine silk webbing.

it is tiny — about the length of a grain of rice — pale yellow-brown, and it folds its wings roof-like along its back. Its back wings are narrow and pointed, with a long fringe of hairs down the edge, like a little feather. The grub is a small white caterpillar you will almost never see, because it lives sealed inside one kernel the whole time it is feeding.

the maize or rice weevil also bores holes, but it is a hard, dark beetle with a long snout that crawls — not a moth that flies up. The flour or meal moth spins lots of tangled webbing and feeds on the outside of broken grain and flour; the grain moth instead bores into whole, sound kernels and leaves that clean round hole with the little window-flap.

This moth lays its first eggs out in the field once the crop reaches the late season — grain hard, cobs drying down, ready to pick. So do not leave ripe grain standing in the field or sitting on the cob any longer than you must; get it in, shelled and dried fast. Every extra day of ripe grain in the field gives the moths a head start into your store.

Grain can look clean on top and be alive with moths underneath, so never judge by the surface alone.

— top, middle and bottom, the corners, and any patch that feels warm — say 5 or more spots. Spread each scoop on a cloth or tray in good light and look right through it for round exit holes, hollow papery kernels and the little window-flaps. Then at dusk, stand and watch the store for moths flying up.

Even one live moth flying up, or one kernel with a round exit hole in your samples, means act now. This is not a field pest where you wait for '2 in 10' — in a warm store a few moths become thousands in a matter of weeks, so treat the first moth or first bored grain as your signal to move.

This moth needs damp grain (about 12% moisture or more) to breed, so dry your grain right down before you store it — until a kernel is so hard it cracks instead of denting when you bite it, or shatters under a stone. Well-dried grain alone starves most of them out, and this drying-and-clean-store routine is the strongest defence you have that needs no chemical, so do it properly.

Shell the grain off the cob and seal it in hermetic (completely airtight) bags or closed drums — shut so tightly that any insect inside uses up the air and suffocates. Before the new crop goes in, sweep out and burn the old grain leftovers, empty sacks and dust in and around the store, and never mix in carry-over grain from last season — that old grain is exactly where the moths hide and cross over into your new harvest. Keep the store cool and shaded.

If you do find them, mix a fine dust right through the grain as you bag it — diatomaceous earth (a soft powder of ground fossil shells that scratches the insect's waxy skin so it dries out and dies) or clean wood ash. It is safe for you to handle and does not poison the grain, but still keep the dust out of your eyes and nose while you work it in. In a large bulk store you can also release Trichogramma — a tiny, harmless wasp that kills the moth's eggs before they ever reach the grain.

If a store is already badly infested, you can mix a registered grain-protectant dust evenly through the grain at exactly the rate on the label, or have a trained, licensed operator fumigate a sealed store with phosphine — phosphine is a deadly gas, so never attempt it yourself. For any grain treatment: cover your skin, nose and eyes, mix in the open air with the wind behind you, keep it well away from children, food, drinking water and animals, and wash yourself well afterwards. Respect the withholding period — the number of days the label says you must wait after treating before the grain is safe to eat or sell. And to stop the moths getting used to the chemical (resistance), rotate to a different chemical group next time instead of using the same product season after season.

empty the store completely, take out and destroy — burn or bury — the badly hollowed, webbed grain so it cannot re-seed the rest, then re-dry and re-treat the sound grain into clean, airtight containers. If a whole batch is already hollow, warm and musty, it is past saving as food or seed — cut your losses: get it away from your good grain and use or sell it quickly at feed value before the moths spread any further.