Remove foliage under BP spline

Hi,

I’m trying to do something but I don’t manage to.
Basically, the idea is, you place a BP spline in your scene, and under this spline, foliage is removed.
I tried with a box collision on the spline, sphere traces to hit the foliage instances, but it didn’t work out the way I wanted.

So what’s the best approach to do this?
I’d like that, if the spline is moved, foliage comes back.