The symptoms begin as small spots, followed by tan to brown necrosis on the leaves.  The pathogen can overwinter on infested plant residue as well as on asymptomatic  hosts near onion/leek fields. Disease management for S. vesicarium is difficults due to growing populations of S. vesicarium  resistant to at least three single-site mode-of-action fungicides.
SLB can result in yield and quality loss of up to 90% in leek and onion crops.  

S. vesicarium can infect a broad range of plant species from several families, including many annual and perennial crop species. 
Field trials in USA and Canada showed that fungicides containing azoxystrobin or pyraclostrobin were ineffective. Similarly, boscalid was highly effective in early trials but declined in efficacy.