Possible blight of mountain mint and New England aster
Hi, starting last year, I noticed the base of my short tooth mountain mint and my New England asters appeared to be going dead in the center, and the stalks were becoming woody and brittle. This year it appears even worse, with many stalks growing to normal height, then just snapping off at the base. Can anyone help me?
Brittle stems can sometimes occur on older established perennials. Pruning them back in dormancy all the way to the ground can help them flush out more vigorous, sturdy growth. In the wild they would get this kind of periodic rejuvenation from grazers or wildfires. If they have been in the ground for three or four years at least, they may benefit from division as well. If you prefer to keep the dead stems up in the winter for wildlife, you can remove them just before new growth starts in early spring.
We see evidence of what looks like rust disease on the underside of the Aster leaves - it is a very common ailment. Removal of infected leaves can be helpful, though no fungicides will be effective at this point. Weakening of the plant from chronic infection could also be a cause for the brittle stems.
There looks like minor leafhopper feeding damage (the lighter flecks) on the plant in the center photo. This is fairly inconsequential and no treatments are recommended.