BLS has a cure - pruning and applying compost tea. I have found that quarantining doesn't do a whole lot to stop the spread. The bacteria that causes BLS (Xanthomonas spp.) is found in nature everywhere, but it can only colonize plants and do damage when the environment cooperates. Think of it this way - a disease needs three things to be successful: a pathogen, a host and an environment. Take out one of these and the process stops.
Pruning goes beyond just picking off affected foliage. Plants also need to be pruned to promote air flow, so plants have a chance to dry off after rain or dew. BLS needs a moist environment to get a foothold on a plant - ensure that the plant's foliage stays dry, and the spread will stop.
The role compost tea plays in this treatment is debatable. Maybe it outcompetes other bacteria before they can cause problems. Maybe it alters the chemistry of the leaf surface so Xanthomonas can't live there. Maybe it stimulates the plant's defenses so it can fend off an attack. The answer isn't clear yet, so I can't speculate beyond that. But I do know that it works.
Over three quarters of my plant had BLS to some degree this spring. Some had only a few spots, some lost about 50% of their leaves. It didn't matter. I picked off all the affected leaves and tossed them in the yard. Then I did some serious pruning to open up the interior of the plant to give them a chance to dry out better. Then I did a lot of foliar applications of tea. None of these steps will stop BLS on its own. But use them together and your plants ought to be fine - I looked at my plants today and there are ZERO lesions on any of the 50 or 60 plants I'm growing this year. Don't give up on them! Good luck!
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