Thanks for your question.

Although you did not specify the type of shrub, I suspect it might be a variety of viburnum.  I can’t determine the precise variety.  If I am correct in my identification, then the dead foliage is most likely attributable to Botryosphaeria canker.  This is a fungal disease that is rather common in viburnum.  It is a disease attributable to various species within the fungal genus Botryosphaeria.

Judging only from your pictures, I can’t tell if the branches bearing the brown leaves are dead or alive.  Try this for the branches with brown leaves:

1).  Lightly scratch away a small patch of outer bark with your fingernail or a clean knife.

2).  Look for the cambial region immediately beneath the bark.  Greenish, moist tissue generally indicates living tissue. Brown, dry tissue suggests the branch is dead.

3).  Repeat the test farther down the branch, toward its connection with a larger stem.

If the entire branch is dead, prune it back to its point of attachment, without cutting into the branch collar.   If only the tip is dead, prune back to healthy wood.  Do not compost the plant debris.  Put into plastic bags that are then sealed and placed out with the trash.  Also remove all plant debris from under the shrub as fungal spores may over winter there.

Do not apply any fungicide at this point (October 2026).  Fungicides will have no effect upon established cankers such as those existing on your shrub.

Start watering your viburnum now and continue doing so up until the soil freezes.  Failure to do this may imperil the survival of the plant during the impending winter months.

Monitor things during spring 2027.  If any brown foliage appears again, repeat the scratch test that I previously described and discard any dead plant material.  Viburnum is a tough shrub.  By continually removing affected branches, the prognosis for your shrub should be good.

See the following for further information on these and related points:

https://apps.extension.umn.edu/garden/diagnose/plant/deciduous/viburnum/leavesbrowntoblackwilted.html

https://www.pubs.ext.vt.edu/450/450-726/450-726.html

https://www.umass.edu/agriculture-food-environment/landscape/fact-sheets/botryosphaeria-canker

Good luck.  Please get back to us if you have further questions.  Thanks for consulting our forum.