Purple blotch is caused by by the fungus Alternaria porri. It is a concern throughout the entire growing season.

●      Infection occurs when fungal spores from nearby plants are blown by wind into onion fields where they infect wounded plants.

●      Overwinters in crop residue on or near the soil surface.

●      Optimum temperatures for infection are between 77-85°F.

SYMPTOMS

Early symptoms include small brown elliptical spots on leaves, similar to IYSV lesions, which enlarge over time and may result in brown, necrotic streaks. Lesions will eventually turn purple as fungal spores develop. In severe cases, lesions enlarge and coalesce to blight the entire leaf. This pathogen requires wounds caused by other diseases (e.g. botrytis), thrips feeding, or hail, to enter the plant.

Management & Control

Considering the losses attributed to infection with purple blotch, it is recommended that the disease be controlled. Various methods can be used, which include the following;

Chemical control

The following fungicide have both preventive and curative capabilities and therefore very effective against purple blotch.

ure 20ml