Purple blotch is characterized by sunken, purple oval-shaped lesions on asparagus spears. The disease also appears in ferns and branches as brown lesions. The disease is caused by the fungus Stemphylium vesicarium and causes significant yield losses (up to 50%) in Ontario. The fungus produces overwintering structures (pseudothecia) in crop residues to survive. It produces sexual spores in the spring season to cause primary infection, followed by secondary spread of the disease by producing asexual conidia in multiple cycles. Rainfall, longer durations of wetness or humid environments with temperatures between 15-30°C will favor disease progress in the field.
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