Polystichum munitum disease?

Hello-
I am a landscape architect and gardener in Portland, OR.  I use Western
Sword Fern/ Polystichum munitum in my own garden as part of a largely NW
native planting palette.  It is a beautiful and dependable plant that
provides year round structure to the garden.
Over the last year I have noticed some problems with some of my ferns and
wonder if anyone might be able to advise or point me in the right direction
for further information.  A few ferns have died back suddenly during the
growing season.  The plants start to exhibit a curling of the pinna along
the fronds.  Within a few short weeks, the plant dies.  The photo below
shows a fern that is currently suffering from this.  You can see one frond
in the middle of the photos that is not yet affected, but the others are
dying-back.  Another piece of information: The afflicted ferns reside under
the canopy of a mature Western Dogwood/ Cornus nutallii that has a chronic
problem with anthracnose.  I used to have the tree sprayed twice a year,
which was marginally effective, but the last two years I have chosen to
forgo the spray regime and see how the tree does on its own.  After some
leaf drop (and clean up on my part), the tree seems to do ok, about the
same as when sprayed.  I do clean up and dispose the leaf litter from the
tree in the fall, as well.
I am not sure what is going on.  I did find an 1984 citation of an article
regarding phytophthora cinnamomi and root rot:
https://www.apsnet.org/publications/PlantDisease/BackIssues/Documents/1984Abstracts/PD_68_536d.htm

I appreciate any advice from you fern experts and afficianados!
Kim Isaacson, ASLA

[demime 1.01d removed an attachment of type image/jpeg which had a name of DSC03605.jpg]

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