Turcicum leaf blight

long, narrow spots on the leaves shaped like a cigar or a canoe — pointed at both ends, roughly the length of your finger (2-15 cm). They start grey-green and watery-looking, then dry to a pale tan or straw brown in the middle.

the spots show up first on the lower, older leaves near the ground, then climb up the plant leaf by leaf. When many spots join together, whole leaves turn brown and dead, and from a distance the plant looks scorched or frost-burnt.

in wet weather look at an old spot in the early morning — it may carry a fine greyish-black dust or fuzz (the fungus making new spores) on its surface, especially on the underside.

with grey leaf spot, whose marks are narrow rectangles boxed in by the leaf veins (straight-sided, not cigar-shaped). It is also not fall armyworm — that pest leaves ragged holes and moist droppings, while this disease leaves the leaf whole but dried and spotted, with no insect and no holes.

from about knee-to-chest height right through tasselling and cob-filling — this is when the plant is most at risk. Step up your checks after a spell of cool, wet, humid weather with heavy morning dews, which is exactly what the fungus loves.

each week walk a big "W" shape across the whole field so you cover the four corners and the middle — not just the edge by the path. Look hardest in the damp, sheltered, shaded low spots where the leaves stay wet longest.

at about 10 stops bend down and inspect the lower and middle leaves — those below the cob — for the cigar-shaped grey-green to tan spots. These lower leaves show it first.

if you start finding these lesions on the leaves below the cob at or just before tasselling — the peak danger point — treat this as your trigger to act, and act sooner and harder if the variety is a susceptible (non-resistant) one and the weather stays wet.

if spots appear only on the lower leaves and the weather is drying out, good field hygiene and a resistant variety may be enough on their own. Keep scouting; the goal is to keep the disease from reaching the top leaves and the cob before the grain is filled.

on a high-value crop where spots are appearing below the cob at tasselling and the weather stays wet, a triazole fungicide can hold the disease back. A triazole is a systemic fungicide — meaning it is taken up into the leaf and works from inside, not just sitting on the surface — so it protects the new growth. Spray at the first lesions, before the disease climbs high; spraying late, once leaves are already scorched, wastes your money.

cover your skin, eyes, nose and mouth, spray in the cool of the morning or evening with the wind at your back, and keep the spray off food, drinking water, children, animals and bees. Wait the full pre-harvest interval (the number of days on the label between spraying and harvest) before you pick, and wash yourself and your clothes afterwards.

don't use the same triazole every time — switch to a fungicide from a different chemical group on the next spray so the fungus doesn't build up resistance (stop being killed by that chemical).

if lesions keep climbing up past the cob despite your efforts, focus on protecting next season — pick a resistant hybrid, clear every scrap of old maize residue, and rotate the field. If the top leaves are already dead and the grain is nearly filled, stop spending on sprays: the loss for this crop is set, so cut your losses, harvest what you can, and put your effort into a clean start next year.