Purple Blotch - Leeks/Onions
Alternaria porri
Pathogen
Fungus
Hosts
Onions and leeks
Symptoms
Spores infect the leaves to produce elliptical lesions which develop a purplish centre and a yellow halo around the outside. These lesions can be several centimetres in length. Under severe disease pressure whole leaves can dieback pre-maturely.
Sporulation leads to the formation of concentric rings.
Development
The lesions can encircle a leaf or stem leading to premature leaf/stem death. Spores can be washed down to the neck area of the bulb giving rise to a watery rot of the outer bulb scales. Spores can also be dispersed by wind.
Overwinters on infected plant debris.
Favourable Factors
Warm, humid weather.
Importance
A disease of leeks, onions and chives.
Losses arise during bulb storage.
Can result in reduced yields with smaller bulbs.
Control
Clean seed, sets or bulbs
Crop rotation
Spray fungicides at the first sign of infection
Remove infected plant debris
