Advice
RHS Help & Advice
Leek rust
Symptoms
Elongated or circular bright orange or brown pustules on leaves and stems.
Cause
Leek rust (Puccinia porri) is related to but different from the rust that infects chives and onions. The rust from leeks does not infect onions, or vice versa.
Mild infections do not render the vegetable inedible, and supermarket leeks frequently show symptoms, but severe infections can lead to extensive leaf death and reduced yield.
Crowded plants, high humidity, excessive soil nitrogen and insufficient soil potassium encourage the disease.
Prevention
Space plants well apart, apply a potassium-rich fertiliser (such as a tomato fertiliser) and practice crop rotation.
Non-chemical control
Remove affected areas of leaf and dispose of them, but not on the compost heap. Ensure all leaf debris is disposed of at the end of cropping. There is some varietal resistance to this disease - check seed catalogues for details of resistant cultivars.
Chemical control
None is available to amateur gardeners.