problem with instance

Hello everyone I wanted to achieve the effect of a background vertical continuous Move through (giving the feeling of going up). I decided to make a plane (with texure) and give the command to transition the y axis. When the plane reaches a certain coordinate should istaziarne a copy to give a sense of continuity. As for the instance I have no problems. The problem is that I clone to infinity. This is my code:

 var planeBackground : GameObject;
 
 var x : int = 0;
 

function Start () {

  planeBackground = GameObject.FindWithTag("Respawn");
 
  
 
 print(planeBackground); 
 
  }
 
  
 
  
 
  
 
 function Update () {
 
  
 
 //print(cameraMia.transform.position); 
 
  
 
  
 

planeBackground.transform.Translate(0,0,-1*Time.deltaTime);

 if(planeBackground.transform.position.y < 1.3){
 
  
 
 print("CLONA");
 
  
 
  
 
  
 
 }
 
  
 
  
 
  
 
  
 
  
 
 }

I will rightly continue to clone because it reached a coordinated derminata will always be lower. How can I fix this? Thank you =)