We try not too, when we used to grow our own plants in nursery beds it was something we did as routine, made sense to spray an acre patch rather than 20 a week later, now we buy in modules and only spray if we need too, since we went to modules we not had more than a few very small patches so not needed to do, saying that Caterpillar is very easy to kill and the spray is relatively cheap, cheap enough to use as part of a programme rather than need to go over the crop again later.
* Thinking of it I have the same 2 litre bottles of Decis in my spray store for about 6 years now but I ima