conditional spawning

Hello all. I have a spawn script which instantiates a ball at given coordinates which works great, however I want the ball to be spawned only after a condition is met and I'm not sure how to go about doing that. Right now my script spawns the ball every 10-15 seconds with a startup time of two seconds and is repeated using invokerepeating. I want the Ball however to be spawned and repeated only after the score is equal to or greater than 50. I tried putting the invokerepeating script into an if statement in the update function but when the score was 50 a ball was spawned every frame. This must be a simple fix ...but I can't seem to figure it out, help please?