Rust

small raised bumps (pustules) that break open like tiny blisters and dust your finger with powder when you rub the leaf — the powder is orange, brown, reddish or yellow, the exact colour of rust on old iron.

the pustules multiply until the leaf looks freckled all over. Badly hit leaves turn yellow and dry out early, starting from the lower, older leaves and climbing upward. On a heavy attack the whole plant can look scorched and the grain fills poorly and shrivels.

check both sides of the leaf — many rusts show most on the underside — and along the stems and pods. The powder wipes off onto your hand; that dusty smear is the sure sign it is rust and not something else.

with harmless leaf-spot diseases, which make flat, dry patches or rings that do NOT rub off as powder, or with sun and drought scorch, which dries the leaf edges without any coloured dust. If nothing comes off on your finger, it is not rust.

rust does its worst from the development stage right through mid- and late-season, so watch hardest from when the plant is growing fast up to and during flowering — the make-or-break time for grain fill. It loves cool, mild days (about 15–25°C) with heavy morning dew, mist or long wet leaves, so step up checks after damp, humid spells.

walk a big "W" across the field so you cover all four corners and the middle, not just the edge by the path. Make about 10 stops along the way.

at each stop, look at the lower, older leaves first — that is where rust starts. Turn leaves over, and rub a leaf between your fingers: coloured powder on your skin means live rust.

the trigger is the very first pustules on the lower leaves, especially just before or during flowering. In plain terms — if you find even 1 in 10 plants with fresh rust powder on the lower leaves at this stage, act now. Rust doubles fast; waiting a week can mean the whole field.

rust cannot be handpicked like an insect — so catching it at the first few pustules is the whole game. The moment you find early rust on the lower leaves around flowering, decide fast: if it is just starting and weather is drying out, tighten scouting; if it is spreading and the weather stays cool and damp, move to a spray while it is still small.

if rust is climbing toward the upper leaves before or during flowering, spray an approved triazole fungicide to protect the top (flag) leaf that fills the grain. Note: a fungicide protects healthy leaf and slows the disease — it cannot revive leaf that is already dead, so spray early, not late. Safety: cover your skin, eyes and nose, spray in the cool of the day with the wind at your back, keep it off food, water sources, children and beehives, wait the pre-harvest interval (the number of days on the label between spraying and harvest) before you pick, and wash yourself and your clothes afterward. Resistance: don't use the same chemical group over and over — rotate to a different fungicide group so the fungus cannot get used to it.

if the rust is still climbing after a spray, rotate to a different fungicide group and re-check the weather — a drying spell will slow it on its own. But if the upper leaves are already yellow and dying across most of the field, the harvest for that leaf is lost — stop spending on sprays, harvest what you can early to save some grain, and next season start clean: a resistant variety, early planting, and burnt or buried residues so rust does not carry over.