Solar beam only works the "you are silenced for the duration of solar beam(standing in it)"-part. If mobs are immun to it, it doesnt work. (For example bosses)
If you kick a boss with solar beam you dont get the buff.
Edit: Not sure if the mobs have to have a cast for it to proc. Or if they just have to be able to get "silenced".(Even if they dont cast anything)
I only tested on target dummies but Entangling Roots and Mass Entanglement work. Mighty Bash works. Solar Beam works as long as the mob can be silenced. It doesn't need to be casting anything nor does it need to be a mob that can cast something it just needs to be vulnerable to silence. Typhoon does not work.
Sometimes typhoon does work, maybe if target isn't immune to disorientation? Although I can't always reproduce it, so I usually use Roots to trigger the effect.