Sugarcane smut

is a whole stool that looks wrong — instead of a few thick strong canes, you get many thin, spindly, grass-like shoots crowded together, short and stunted, with narrow pale leaves. This 'grassy' clump means the plant is sick inside even before the whip shows.

is the smut whip: a long, curved, black, whip-like shoot — like a thin black bootlace or a rat's tail, often as long as your arm — pushing straight up out of the top (growing point) of the cane. When young it has a thin silvery-white skin; once that skin breaks it turns sooty black and puffs out clouds of black powder (the spores) if you shake it or the wind blows.

the whip comes from the very top of the shoot, from the central growing point. The affected canes stay thin and light and give little juice or sugar.

with normal flowering (the cane 'arrow', which is a feathery silver-grey plume, not a hard black whip) or with fall armyworm or borer damage (chewed leaves and holes, not a black whip). A black, powdery, whip shape from the growing tip is smut and nothing else looks like it.

— these are the stages when whips push out and shed spores. Pay closest attention to ratoon (regrown) fields and any field you planted from cane of unknown health, which carry the most disease.

Walk a big "W" across the field so you cover all four corners and the middle, not just the edge by the road. Make about 10 stops, and at each stop look over roughly 10 stools.

At each stop, scan the tops of the shoots for the black curved whip, and look down at the base of the stool for crowded thin grassy shoots. Both are smut.

There is no 'safe' number — a single whip is already shedding spores onto the rest of your crop. The moment you see a whip, rogue it (see control). If you are counting many whipped stools, that field is heavily infected and should be ploughed out, not ratooned again.

Choosing a smut-resistant sugarcane variety is by far the most effective control. If smut is in your area, ask your extension officer or mill for the resistant varieties and switch to them — a resistant variety fights the fungus for you, season after season, at no extra cost.

Take your seed-cane (setts) only from healthy, disease-free plants or a clean nursery — never cut planting material from a field that has had whips. Do not carry cane from an infected field to a clean one; you will carry the spores with it.

where this is recommended: soaking the setts in hot water kills the fungus hiding inside the buds before it can start. Ask your mill or extension officer for the correct water temperature and soaking time.

Before the whip breaks open and dusts spores, gently slip a bag or old sack over the black whip, cut the whole shoot low, and carry it out inside the bag so spores don't scatter on the way. Then burn or bury it deep well away from the field. Pull out the whole infected stool where you can — remember there is no cure, so the stool will only keep making whips.

The only chemical use is a seed-treatment fungicide: after hot-water treatment, dip the setts in a systemic fungicide (systemic means it soaks into the sett and works from the inside) before planting, to kill bud-borne infection. When handling any fungicide, cover your skin, eyes, nose and mouth, mix and dip in the cool of the day out of the wind, keep it away from food, drinking water, children and animals, and wash your hands and clothes well afterwards. Follow the label exactly. No spray will save cane that is already infected in the field.

if whips keep coming back and many stools are grassy and whipped, stop ratooning that field — do not leave the stumps for another crop. Plough the whole field out and start again with a resistant variety and clean, treated setts on fresh ground. Cutting your losses and replanting clean is cheaper than nursing a heavily infected field that will only get worse and infect your other cane.