First Report of Severe Outbreaks of Bacterial Leaf Spot of Leafy Brassica Greens Caused by Xanthomonas campestris pv. campestris in South Carolina

Suppression of Bacterial Blight on Mustard Greens with Host Plant Resistance and Acibenzolar-S-Methyl

Bacterial blight, caused by Pseudomonas cannabina pv. alisalensis, attacks the leaves of most brassica vegetables, including mustard greens (Brassica juncea). 'Carolina Broadleaf,' a new mustard cultivar, is resistant to bacterial blight, whereas 'Florida Broadleaf,' a commonly grown cultivar, is susceptible. Acibenzolar-S-methyl (trade name Actigard) has been used to manage bacterial diseases caused by P. syringae on a variety of crops. The objective of this study was to evaluate host plant resistance and acibenzolar-S-methyl alone and in combination to manage bacterial blight. Three field experiments were done in spring and fall 2011 and fall 2014. In each experiment, acibenzolar-S-methyl was applied twice as a foliar spray, once before and once after plants were inoculated. Severity of bacterial blight was 81% less on nontreated Carolina Broadleaf than on nontreated Florida Broadleaf (P ≤ 0.0003). Acibenzolar-S-methyl applications reduced severity of bacterial blight by 55% compared with the water control treatment on susceptible Florida Broadleaf. Mean weight of diseased leaves, averaged across acibenzolar-S-methyl treatments, was 53% less with Carolina Broadleaf than with Florida Broadleaf (P < 0.0001). However, acibenzolar-S-methyl applied at the recommended rate (14.2 g/ha) significantly injured leaves of Carolina Broadleaf in two experiments and injured leaves of Florida Broadleaf in one experiment. Overall, host plant resistance was more effective than acibenzolar-S-methyl for managing bacterial blight on mustard greens.