Arugula being grown in a greenhouse as microgreens was found to be infected with bacterial leaf spot, most likely Pseudomonas syringae pv. alisalensis, the only described pathogen of arugula and other cruciferous species. This pathogen may be seed-borne and survives in plant debris for up to two months.
To manage bacterial leaf spot, begin with certified disease-free seed or hot water treated seed. Remove and destroy all crop debris between plantings. There are few effective controls for plant pathogenic bacteria; although copper and hydrogen dioxide may give fair control if applied early in the disease cycle and repeated at regular intervals. Check pesticide labels for host appropriateness. Hydrogen dioxide is a disinfectant only and has no residual activity.