Septoria Leaf Spot is most prevalent during warm and wet weather. Mulching is one means of control as is pruning from the ground up. Keeping infected leaves picked off helps keep this under control as well. Some fungicides can help keep leaves from becoming infected but will not cure infected leaves. Perhaps this from ATTRA will be of some help.

https://attra.ncat.org/calendar/question.php/what_organic_controls_are_there_for_sept

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