Rust: how to recognise and treat it

Disease

Symptoms

Pale spots on the upper leaf surface, with raised powdery pustules mostly underneath; on beans they often have a yellow halo.
Pustules are orange, yellow, brown, black or white depending on the rust; many turn dark in late summer and autumn.
Badly affected leaves turn yellow and fall early; pustules can also appear on stalks, stems and pods.
Heavy infection weakens the plant; a few rusts, such as antirrhinum rust, can kill it.

Pick off the first affected leaves as soon as you see them — but only a few; stripping many leaves does more harm than good.
Remove badly affected plants, which release huge numbers of spores; do not compost rusty leaves from late summer on, when they carry tough overwintering spores.
Sulfur on plants its label covers, as a protectant at the first spots; it does little once rust is established.

On roses and other ornamentals — a fungicide with tebuconazole + trifloxystrobin; follow the label.
On edible crops — in the UK no fungicide with good activity against rust is available to home gardeners; elsewhere use only a product labelled for that crop and follow its dose and pre-harvest interval.

Reference information, not a guarantee. Read and follow the label of any product: dose, safety and the days to wait before harvest.

Choose resistant varieties where they exist, for example of beans, currants and gooseberries.
Water at the base in the morning, and space or thin plants so the leaves dry quickly — rust needs wet leaves.
Avoid excess nitrogen fertiliser, which gives soft growth that rust colonises easily.
Clear plant debris at the end of the season, rotate beans, and do not save seed from rust-affected crops; plant currants and gooseberries well away from five-needled pines.

Figures checked against these sources.