Why are my plants floating?

I started to make a map on left 4 Dead. When I started to create the grass I made a Displacement and started to paint the alpha, being the plants. In hammer they looked like they were floating, but I thought it would go away in game. When I started playing I noticed all my plants were floating looked cut off at the top. Anybody got any ideas?

http://img26.imageshack.us/img26/5089/floatingplants.jpg

Go to Map>Map Properties and change Detail Material File to “detail/ruraldetailsprites” without the quotes ("").

Thanks. It worked.