Howard F. Schwartz, Colorado State University, Bugwood.org

onion purple blotch, disease, Alternaria porri

Howard F. Schwartz, Colorado State University, Bugwood.org

onion purple blotch, disease, Alternaria porri

Howard F. Schwartz, Colorado State University, Bugwood.org

disease, onion, purple blotch, Alternaria porri

Howard F. Schwartz, Colorado State University, Bugwood.org

onion, purple blotch, disease, Alternaria porri

Howard F. Schwartz, Colorado State University, Bugwood.org

onion purple blotch, disease, Alternaria porri

Howard F. Schwartz, Colorado State University, Bugwood.org

A volunteer onion plant with the purple blocth disease caused by Alternaria porri in a winter wheat field

Howard F. Schwartz, Colorado State University, Bugwood.org

An onion plant with the purple blocth disease caused by Alternaria porri in the field.

Howard F. Schwartz, Colorado State University, Bugwood.org

An onion field during the mid stages of the purple blocth disease caused by Alternaria porri trial in the field.

Howard F. Schwartz, Colorado State University, Bugwood.org

A field trial of onions for the purple blocth disease caused by Alternaria porri.

Howard F. Schwartz, Colorado State University, Bugwood.org

An onion fungicide test plot at Vineland used in the study of onion purple blotch caused by Alternaria porri.

Howard F. Schwartz, Colorado State University, Bugwood.org

Purple blotch lesion on the neck region of an onion plant caused by Alternaria porri.

Yuan-Min Shen, National Taiwan University, Bugwood.org

Black to purple spot on stem of Allium