Mowing down an Instanced wheat field with weightmaps?

[RealBeard]

Hi Everybody.

So I'm attempting to simulate a car mowing a path through a wheat field as it drives.

I have a constrained cube that uses a distance to geo operation that paints a weightmap to a grid as it moves with the car.
The grid in turn uses said weightmap to drive the particle size of the emission instancing the wheat geo.

My problem is that the animated weightmap doesnt affect the particles when the emission type is set to "Total Number of Particles" (To achieve the full field.)
Is it possible to achieve this? Is there an every nth frame or test function I should be using?

Originally I wanted the instanced geo to "rotate flat" in the direction of the cubes path, but at this point I'll settle for simply making the wheat dissapear.

Help/input is much appreciated!

[Pooby]

If the particle tree is simulated, then any changes to the weightmap are irrelevant past frame 1. The particles are generated on the first frame and just sit there waiting for further instruction.
It is only on a non simmed tree that it will read that weightmap and use it to generate the particles per frame.
If you want to delete them on a simmed tree, then do it with a delete point node and use some kind of condition such as weightmap is less than, or distance to 'whatever' is less than (or any condition you like) to produce the required Boolean to plug into it.

[RealBeard]

hmm, this still doesn't work. The animated weight painting by geo itself has to be simulated or else it doesn't work, is this interfering with the particles? Even when the particles in point cloud are non simulated there seems to be no effect. Though the filtering works perfectly in non-sim state when the particles are set to a Per Second. Please excuse my ignorance.