I suspect the "we only have protective chemistry now" story is just more chemical industry lies designed to get us to apply more sprays even if there is no disease showing, personally I'm sick of their crapProbably not but how quick can you react if things do change.
I can't see any point putting product on if no disease is there but bear in mind septoria has a longish latent period so disease may be there but just not showing and once disease is present most Chems are now mainly protectant with not great curative activity.
As mentioned in the t0 thread I'm doing mine with amistar opti next week because I'm growing jb Diego but hopefully t1 will be azole+ctl and then we'll see what things are like at t2 it may get a sdhi if needs be but it may get another azole+strobe+ctl (assuming no strobe added at t1)
I'll also be playing around with just foliar nutrition again as that worked ok last year but needs more fine tuning.
The main thing is to be flexible and react to what's happening at any given time and being able to react and adapt.
My rough thinking at the mo is £50/ha if using old chem or £75/ha if I include a sdhi at t2.
Ps we has 10mm in the week and have just had another 7mm today, it's not enough but will keep us going for another week or so.