Onion rust

Affected leaves show small reddish to dusty orange spots (pustules). These later turn black and are covered until maturity by leaf epidermis. Leaves that are heavily infected turn yellow and die prematurely. A new crop of leaves may develop and the bulb size is usually reduced. The fungus attacks also leek, shallot and some wild species of Allium. The disease is favoured by high humidity coupled with moderate to low temperatures. Also excessive nitrogen in the soil favours disease development.