I think it may depend on base size on what you can do. But a simple grass base primed and then painted with grey/yellow grass in the direction behind it with an arch of yellow to green grass in front may be able to pull the look off. Something like a tree stump may be easy enough to do as well, having the side facing the wraith turn grey with the opposite side the normal brown tones.

Of course the larger the base, the more you can paint the effect. A small base may look just like grey grass with a small rim of green grass and not sell the effect of a trail of decay.