i did not see anything under options to turn grass completely off just set it to low/med/high
However i did some dig through the D2 folder and found what I was looking for. For anyone else who would like to turn off grass its in ..

Divinity II - DKS\data\globalswitches.xml

<!-- LoadVegetation: Set to 1 to load all vegetation. -->
<!-- Set to 0 to not load any grass or other vegetation (may increase framerate on low-spec pc's). -->
<!-- DEFAULT = 1

the actual value to change appears at the end of the globalswitches.xml
LoadVegetation="0"

this completely removes grass.

Thanks for your reply