how do i destroy a spawned object

first off all sorry for my english i'm dutch and can't speak english that well

also i'm new to unity

click here to see picture

what i want is to have a box collider and when i step in it it spawns an gameobject.

i already have that but now i need another box collider that will destroy that same object.

this is my code

 #pragma strict
 
 var Blokkade : GameObject;
 var spawnposition;
 
 function spawn_blokkade  ()
 {
 spawnposition = Vector3(0,0,-50);
 var temp_spawn_blokkade = Instantiate(Blokkade, spawnposition, Quaternion.identity);
 }
 
 
 
 function OnTriggerExit(o:Collider){
 spawn_blokkade();
 }
 
 function OnTriggerEnter(o:Collider){
 
 }