Onion Disorder: Purple Blotch

Publication cover

Publication cover

Karen Delahaut, Walt Stevenson
Revised:  8/6/2012
Item number:  A3804

Purple blotch causes onion leaves to become blighted and die prematurely. The result is reduced yields from undersized and immature bulbs. In storage, diseased bulbs rot.

This disorder affects onions, garlic, leeks, and false shallot. The fungus that causes purple blotch (Alternaria porri) is closely related to the species that causes early blight on tomatoes and potatoes (Alternaria solani). This fact sheet will help you identify, prevent, and control purple blotch on onions and related crops in your home garden.

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