Thanks for your question.

We believe these structures on the leaves of your Liatris are galls. Within these structures are very small gall midge larvae. I don’t know what species they are. What has happened is that adult midges laid eggs on the Liatris leaves this past spring. When these eggs hatched into larvae, the larvae burrowed into the leaf tissue. This triggered a growth response within the leaves that led to these larvae being completely enclosed by plant tissue. These are the bumps that you are seeing on the leaves. These bumps are called galls. No harm occurs to the plant in this process. Only cosmetic damage is done. While you could remove the affected leaves, there is no reason to do so. There is no remedial action that needs to be taken by you. With time, the larvae burrow out of these galls and become adult midges. These adults then mate and lay eggs. When these eggs hatch into larvae, the process begins all over again.

Without pictures of the other plants that you think are being impacted, I do not know if gall midges are involved or not. Since these midges are generally very plant specific, it is unlikely that something has spread from the Liatris to these other plants.

Here is some general information about this type of insect:

https://ipm.ucanr.edu/PMG/GARDEN/FLOWERS/INVERT/gallmidge.html - :~:text=For flowers in planting beds,difficult to control with insecticides.

https://extension.umn.edu/yard-and-garden-insects/insect-and-mite-galls

Good luck. Please get back to us with any further, related questions. Thanks for using our forum.