Disease
Rust
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Watch for | Watch for in April | Watch for in May | Watch for in June | Watch for in July | Watch for in August | Watch for in September | Watch for in October |
What it is
Rust is a family of fungal diseases, each type usually confined to one plant or a small group. In the vegetable garden, leek and garlic rust and broad bean rust are the ones you are most likely to meet; among herbs, mint rust is common; and in borders, roses, fuchsias and heucheras are frequent targets. Infections look alarming but crops are usually still edible.
Symptoms
Raised, powdery pustules appear, coloured bright orange, rusty brown or almost black, depending on the type and the stage. Leeks and garlic carry orange flecks along the leaves; roses show orange spots under the leaves and on stems; mint shoots in spring can be pale, swollen and twisted before pustules form. Heavily infected leaves yellow and die off early. Rubbing a pustule leaves coloured dust on your finger.
Cause
Spores are carried on the wind and need moisture on the leaf to germinate, so humid weather and crowded planting help it along. Allium rusts are often worst in late summer and autumn, especially on soils rich in nitrogen and low in potassium. Many rusts overwinter on fallen leaves or in perennial hosts, and mint rust persists in the underground runners.
Control
Remove and bin badly affected leaves as soon as you see them, and clear up debris at the end of the season. Leeks with rust usually still produce a usable stem, so peel away the outer leaves and eat them. For mint, cut the patch to the ground in autumn, or replace it with clean runners in fresh compost. Fungicides are rarely justified; use one only as a last resort and follow the label.
Prevention
Space plants so air moves freely and avoid heavy nitrogen feeding. Rotate allium and bean crops each year, and do not plant leeks right next to a previous rusty crop. Choose varieties sold as rust resistant, which are available for leeks, garlic and some roses.
Plants often affected
Could it be something else?
These problems share some of the same symptoms. Compare them, or run the symptom checker with these signs ticked.
Months to keep an eye out: April, May, June, July, August, September and October.
Sources
Identification and life-cycle details were checked against the references below. Text and advice are our own. See our editorial policy.