Q What is leek rust?

A This is a very common and destructive disease that seems to be on the increase.

If your leeks get long, bright-orange spots on their leaves in warm (10-24°C), moist weather, where the leaves are wet for at least four hours (usually from August onwards), you probably have a leek-rust problem.

Garlic and chives can also be affected. Similar species attack other onion-family crops but aren’t very common. 

Caption: Orange rust spots appear from late summer

Q What damage does it cause?

A Sometimes the foliage is ruined and the growth of the plant reduced. Even if the plant is not affected like this, the foliage is most unappetising. Later, when the weather turns colder, the leeks slowly recover from the disease, producing unaffected leaves. However, this might not be until December in a mild autumn.

Q How can I avoid leek rust?

A Too much nitrogen and too little potash in the soil is said to promote leek rust so be careful when adding fertiliser.

The pustules are full of uridiniospores that spread the disease to plants by rain splash and wind currents so don't plant them too close together.

They also persist in the soil on plant debris for several years so clear all of the old crop and put it in the bin or burn it. 

There are no chemical controls available.