Pacific Northwest 1998 An Online Guide to Plant Disease Control

FactSheets offer superior print quality for the page you are currently viewing. Using Microsoft's Internet Explorer has given best printing results.
Glossary
Guide Home
Search

OSU Extension Office
 
Onion (Allium cepa) -- Smut
 
Cause: Urocystis magica (syn.= U. cepulae) and U. colchici, fungi that survive many years saprophytically in infested soil. They attack only members of the onion family including onion, leek, and Welsh onion and are more a problem on muck soils. Susceptibility decreases as tissue ages. Affected bulbs are predisposed to other infections in storage.
Symptoms: The disease appears in the plant stem as it emerges. Infected areas have a raised, blisterlike appearance near ground level. Blisters rupture to expose black powdery spore masses. Many seedlings die during emergence; those that live produce distorted bulbs with darkish streaks and numerous smutty lesions.

Note the black, dusty lesions along the leaves and bulbs.

 
Cultural control: Small onion sets and young onion plants may be set out in infested soil without apparent danger of infection.
Chemical control:
  1. Seed treatment.
    1. 42-S Thiram at 6 fl oz/100 lb seed plus a dye. See label for reentry restrictions.
    2. Pro-Gro at 2.5 lb/100 lb seed. See label for reentry restrictions.
  2. Control smut by an in-furrow drench at seeding.
    1. Dithane DF Rainshield NT at 3 lb/A in 75 to 125 gal/A water. Dry bulb onions only. 24-hr reentry.
Content edited by: Cynthia M. Ocamb on January 1, 2010
 
Top

In print since 1954 and on the web since 1996. Questions or comments, please contact us.