Generalized disease and planthoppers
A friend had me over to see why her hypericum was dying back. After a “brief” search, we found planthoppers on everything from nandina, mountain mint, magnolia, maple trees, dogwoods, asters, etc. The grasses and ferns did not appear affected. All are exhibiting similar signs: diffuse yellow marbling of leaves, leaf/plant die back, all very rapid. It started in the hypericum last summer. The hypericum is severely affected, dying stem by stem. My theory is the planthoppers are spreading something. What? I’m not sure. How to rid the property of planthoppers (they are everywhere) to help stem the spread? I don’t know. It could be a wilt/virus/bacteria that has just allowed the planthoppers to proliferate more readily. It’s a real chicken or egg situation. I have more photos if needed. Thanks for reviewing!!
Montgomery County Maryland
Yes, planthoppers are abundant but they aren't to blame for what you are seeing.
As for their abundance, it is normal at this time of year, and they are likely food for another critter down the chain.
Here is our page about them: https://extension.umd.edu/hgic/topics/planthoppers-flowers
We'd really need to do more individual plant concerns as many diseases and pests are host specific.
Certainly environmental/abiotic factors like weather, soil, etc. could also be in play. Hypericum can suffer from several issues including a root rot by the fungus Rosellinia among others. How does that particular area drain?
If you can send new questions and photos for each (or a couple) of plants we will take a look.