There was another thread with similar bronzy leaves where it was suggested it was due to cold temps (plant producing fall colors). Does your plant experience cold temperatures at night?
I would say N has been reduced too much too. But, the bronzy stuff looks odd.
Hey bro! Just to share with ya.
Yes cold does express colors that way - nice question for that value.
The thing is that K does the same thing - When done together, you can get very rich and deep coloring...once you dial the combination in!
I say it's bloom feeding because it shows exactly the result of early P&K enhancement. It (plant) thinks it's further along then it is from the high P uptake and is using more N from the plant then up taking it. The color expression and bronzy look point straight to the elevated K.......so then - early use of high P&K bloom foods is indicated.
A little more N MIGHT slow down the progression but, only if the PK is reduced for say maybe a week.....With it having around 4 weeks left it would be slightly risky to try that now but could slow the progression for a better yield.
The use of Si from the start of the run will help regulate P uptake......The plant stores P and when that limit is reached - boom P tox starts....The higher the P content of the feed - the faster it takes over.
Just thought I would share that..
Doc