Over the past four or five days I have noticed in my own garden dozens of perennials from a wide group of genera showing the same foliar disease symptoms; countless dark spots on leaves slightly to severely curled and in some cases the plants appear to have blackened leaves severely curled and falling from the plants almost denuding it. Similar symptoms are also showing on my Black lace elderberry…
I don’t own a microscope or anyother instrument to guarantee accuracy of diagnosis, but I offer the following as a general rule: If the same symptoms ravage a wide variety of plants of different genera, the disease agent is probably bacterial, rather than fungal or viral.
A minority of my diseased plants are recently showing recovery, that is, the new foliage appears healthy, free of infection. So from that I suspect the frequent rains we had for most days of more than two weeks in succession, caused the bacteria to develop and spread, and it did so quickly. With the drier conditions returning, the suspected bacteria no longer can thrive without a reliable continuing presence of moisture. I shall have to wait to know if some of the plants more severely diseased ( Angelica, Ligularia, Sambucus, Geranium) will recover.
Fungi generally infect plants within a genus or family and are unable to cause such havoc to such a wide variety of unrelated deciduous broadleaf plants.