Pseudomonas syringae pv. alisalensis - UMass Extension
In January 2017, there were two nights when the temperature went down to the low 20's, followed by multiple days of heavy rain. This created an environment in which some of my arugula leaves got small black spots, with smaller white spots (dead areas) inside the black spots. Looking online, the best visual match I found was Pseudomonas syringae pv. alisalensis, which is a very common plant pathogen. According to the UMass Extension page, Pseudomonas syringae is the only pathogen of plants in the family Brassicaceae.
Pseudomonas syringae pv. alisalensis on arugula leaves on January 29, 2017
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