Leaf rust

small orange-brown, rusty spots on the upper side of the leaves, scattered and separate like grains of chilli powder or brick dust. Rub your thumb across them — they smear an orange-rust powder onto your skin. That powder is the spores.

the spots (called pustules — little blisters that have burst the leaf skin) grow more numerous, and the leaf around them yellows and dries early. Under a heavy attack the lower leaves brown off and die while the plant is still trying to fill grain. Late in the season the pustules darken from orange to black.

mostly on the leaf blade, spread over the flat upper surface in no set pattern. This matters — leaf rust rarely gets onto the stem.

stem rust makes bigger, darker brick-red pustules mainly on the stem and leaf sheath, and they tear the skin roughly. Stripe (yellow) rust lines its yellow pustules up in neat stripes between the leaf veins, not scattered. If your spots are orange, round, powdery and scattered on the upper leaf blade, it is leaf rust. Plain yellowing with no powder that rubs off is hunger (nitrogen) or drought, not rust.

start walking the field once the crop is jointing and building height (the development stage) and keep going hard through heading and grain-fill (mid-season) — these are the stages when rust does the most damage, and warm, misty, dewy mornings after mild nights are exactly the weather it loves. Check after every such spell.

cross the field in a big "W" so you hit all four corners and the middle, not just the headland by the path where you always look.

make about 10 stops along the W. At each stop look closely at the top two or three leaves of 5–10 plants — the upper leaves, and above all the flag leaf (the top leaf that feeds the head).

turn the leaf to the light and look for the first orange, powdery spots; rub a finger over any suspect spot — orange dust that comes off confirms live rust. Pay special attention to plants of a known susceptible variety.

you are already at threshold when you find the first rust pustules on the upper leaves at or just before heading, especially on a susceptible variety — in plain terms, even 1 in 10 flag leaves showing fresh orange pustules as the head emerges → act now, because from there it explodes. Waiting until half the field is orange is waiting too long.

plant a wheat or barley variety bred with durable leaf-rust resistance. This is the single most effective control — it cuts rust roughly two times out of three on its own, costs nothing extra at spraying time, and protects even when the weather turns against you. Ask your seed supplier or extension officer which local varieties still hold up to rust.

plant early so the crop passes through heading before the main rust weather builds up; pull out or plough down volunteer wheat and barley and roadside cereal regrowth — this "green bridge" is where rust survives between seasons and re-infects your new crop; and do not overdo the nitrogen, because lush, soft, over-fed leaves catch rust worse. These habits together take the edge off the pressure before rust ever arrives.

there is no biological spray or handpicking for rust — the two things that stop it are the resistant variety above and, if you planted a susceptible one, spraying at the very first pustules. A spray protects the green leaf you still have; it cannot bring back leaf that has already dried, so timing is everything. Once you see those first spots on a susceptible variety, decide quickly.

if you are stuck with a susceptible variety and rust appears, spray a triazole fungicide (a systemic product — meaning it moves inside the leaf, unlike a contact spray that only coats the surface). Time it to protect the flag leaf at the first pustules; well-timed it controls rust strongly (about eight times out of ten). Safety: cover your skin, eyes, nose and mouth, spray in the cool of the day with the wind at your back, keep it off food, drinking water, children and bees, wash yourself and your clothes afterwards, and respect the pre-harvest interval (the number of days the label says you must wait between the last spray and cutting the crop) so no residue reaches the grain. Resistance: don't lean on the same product every season — rotate to a different chemical group so the fungus doesn't learn to survive it.

re-check the flag leaves a week after spraying; if fresh orange pustules keep appearing on the green leaves and the weather stays mild and dewy, a second, well-timed triazole spray on a different group may still save the flag leaf and the grain-fill. But once the flag leaves are already brown and dry and the heads are near ripe, stop — no spray will heal them. Cut your losses, harvest promptly to save what grain has filled, and then break the cycle for next season: clear every volunteer cereal, rotate to a non-cereal crop, and plant a resistant variety so rust has nothing to carry over on.