Teff shoot fly

on a young seedling the innermost central leaf turns yellow, then brown, dries out, and slides out easily when you pull it gently — while the outer leaves around it stay green. ('Deadheart' just means the growing heart of the shoot has been killed.) The little base you pull out is often soft, rotten and bad-smelling.

Around the deadhearts you'll see stunted, off-colour seedlings, gaps and thin bare patches in the stand, and hit plants throwing out a bush of many weak, thin side-shoots (tillers) that never make good grain heads.

is small and grey — smaller than a common housefly, the colour of ash — and you'll catch it resting on or running over the young leaves in the warm part of the day. It lays tiny white eggs, like slivers of rice, on the seedling leaves.

is the real culprit: a tiny pale, legless grub, shorter than a grain of rice, found down inside the leaf sheath or in the rotten base of a deadheart when you split the little stem open.

Dry-weather wilting droops the whole seedling and the central leaf will not pull out cleanly; a nitrogen shortage yellows the older, outer leaves evenly right across the field. Only shoot-fly deadheart kills just the central leaf, lets it slide out easily, and leaves a rotten, smelly base — often with a maggot inside.

— roughly the first three to five weeks, which is its whole vulnerable window. This is when a maggot can still reach and kill the central shoot; once the stems start to lengthen, the crop has grown out of danger.

— that is when the flies are busiest and your seedlings are most exposed.

Walk a big "W" across the field so you check the middle and all four corners, not just the edge by the path. Make about five stops.

At each stop, look closely at about 20 seedlings: pull gently on the central leaf of any stunted or off-colour one to test for deadheart, and split open a few weak stems at the base to hunt for the pale maggot.

— or when you see the little grey flies busy over the young stand on a warm day. At that level the pest is building and your youngest seedlings need protecting now.

plant early, before the warm-weather flies build up, and at the recommended higher seed rate so the crop comes up thick and races through the tender seedling stage. Use a firm, well-prepared, moist seedbed and enough nitrogen for quick, vigorous early growth. A dense, vigorous stand simply outgrows the fly, and the extra plants make up for any that are lost.

clear away volunteer teff and grassy weeds in and around the field — these are the fly's hideouts and alternate homes where it breeds up. And sow your whole field at once, not in dribs and drabs; staggered planting keeps handing the fly a fresh supply of young seedlings to breed on.

Before sowing, treat the seed with an approved systemic seed treatment ('systemic' means the chemical is taken up inside the plant and protects the seedling from within for its first weeks), or spray an approved insecticide on the seedlings early, while they are still in the vulnerable stage. A spray cannot reach or revive a maggot already sealed inside a dead central shoot, so early timing is everything.

cover your skin, eyes, nose and mouth; spray in the cool of the morning or evening with the wind at your back; keep it well away from food, drinking water, children, animals and bees; respect the pre-harvest interval (the set number of days the label tells you to leave between the last spray and cutting the crop); and wash yourself and your clothes afterwards. Treated seed is poison — never eat it or feed it to animals, mark the bags clearly, and keep it from children. To stop the fly building resistance, rotate to a different chemical group rather than using the same one season after season.

You cannot save a seedling whose heart is already killed, so keep the weeds down and the nitrogen up to push the healthy plants and their side-tillers to close the gaps. If a patch is badly thinned and the season is still young, re-sow or gap-fill it now while there is still time. And once the crop is past tillering and the stems are lengthening, it has grown out of danger — stop spending on sprays, let it finish, and plan to plant earlier and treat your seed from the start next season.