Most of  the literature states that JB grubs feed not just on lawn roots, but on the roots of other ornamentals.  However, I am not aware of significant damage the grubs cause to shrub roots.  My guess is that the grubs have a specific soil-depth preference, and that the shrub roots are more extensive than shallow-rooted lawns and so can withstand any JB feeding.  Furthermore, grub treatments use pesticides that are highly toxic to pollinator species, so I would not recommend using them to treat what is likely a non-issue.

Hi Dennis-