part of the tree dying

Question

my eucalyptus tree [established] has gone brown on several branches and can be snapped off. Also a new hydrangea shrub has gotten the same brown leaf and seems to have died.

Answer 1

These articles discuss diseases of the plants that you are referencing.
https://www.gardeningknowhow.com/ornamental/trees/eucalyptus/eucalyptus-tree-problems.htm
https://www.gardeningknowhow.com/ornamental/shrubs/hydrangea/common-hydrangea-diseases.htm