Leek rust, Puccinia allii, is a common fungal disease of leeks, also occurring on chives and garlic, and sometimes on onion and other members of the Allium family. Despite its appearance, it rarely does serious damage to the edible part of the plant.
Powdery red/orange, slit-like pustules develop on leaves and stems. These first appear during the summer. Infection usually declines in the cooler weather of autumn so that later growth is disease free. In mild autumns there is a risk that the disease will continue to develop. With very severe attacks leaves may turn yellow and die, and plant size may be reduced.
Fungal spores are carried in the wind. Spores germinate when they land on suitable host plants. The disease occurs most frequently under conditions of high humidity and low rainfall that favour spore germination. As the disease develops, orange pustules containing further spores are formed and the cycle of infection continues. This particular rust only infects leeks and closely related plants (i.e. the onion family). The fungus survives because the growing season for these crops extends over most of the year and some form of diseased material is invariably present as a source of infection.
Prevention and control
Once the disease is present on the plant, there is no control possible. If only a few plants are affected, removing and destroying them may prevent further spread. Unless the attack is severe it can usually be tolerated with no serious loss of yield.
- Hygiene: Always remove and destroy infected plants and crop debris before planting any new crops of the onion family.
- Cultural control: Ensure good drainage. Use a crop rotation of preferably four or five years.
- Correct feeding: Have a soil test done to check nitrogen and potassium levels. It seems that plants grown on soils high in nitrogen and low in potassium are more susceptible to attack by leek rust. Use only well-rotted manure (fresh is high in nitrogen). If soil potassium level is low use a seaweed dressing, or a commercial organic fertiliser known to be high in potassium.
- Resistant varieties: Choose leek varieties that show some
resistance or tolerance to the fungus, e.g. Alcazar RZ, Swiss Giant Zermatt,
Ardea, (check seed catalogues for other varieties)