Generation Problem c#

I have a question-problem with a game I'm creating for android .... the thing is that I have 4 generators but I want to only 1 generator generating items from the beginning, then the 2nd generator starts to generate once you have accumulated too much x points and so on with the other.

I tried to, but if I put it in Start() does not generate anything when it comes to points, I will change to Update(), FixedUpdate() and generated once reach the points but starts to generate thousands of items xD

Actual Code: http://pastebin.com/rNNumw0u