I used to have alot of black eyed susans. last year the leaves got black,...
There are two primary disease that cause black-eyed Susan leaves to get black spots that progress to black blotches and sometimes totally black leaves. Septoria is more common this year.
Management for both Angular leaf spot and Septoria leaf spot are the same. Plants are not usually killed, but can die back to the base.
To manage them, do not water overhead. Keep plants thinned so they have good air circulation and dry quickly after rains. At the end of the season (or earlier is the plants look dead), remove all infected plant material and discard in the trash so that infected material will not reinfect them next year.
You can spray with a fungicide containing copper or chlorothalonil for Septoria (a fungus.) You can use a copper containing bactericide for Angular leaf spot.
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