Ring spot is caused by the fungus Mycosphaerella brassicicola. The disease is most severe during cool weather when heavy dews are present. The pathogen is disseminated within and among fields by windblown spores (conidia), and overwinters in infested crop debris.
Ring spot symptoms first appear as small, whitish leaf spots. Lesions enlarge with time, and become elongated and purple to gray in color with lighter centers. Perithecia (fungal fruiting bodies) appear as dark specks in lesions. Lesions may coalesce and completely blacken large portions of the plant. The disease is not considered important.
Biological control strategies have not been developed for ring spot.
Practice three-year or longer rotation to non-hosts such as small grains. Eliminate weeds in and around fields.
No fungicides are registered specifically for ring spot.
Categories: Canola and Mustard, Disease, Ring Spot
Date: 12/31/2004