rust on leeks

Space plants well apart in the first place, 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, best to burn or bag and bin. 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.

No chemical control is available to amateur gardeners.

Crowded plants, high humidity, excessive soil nitrogen and insufficient soil potassium encourage the disease.