whoa whoa, its not burned at all. let me explain; nute burn occurs at the new growth tips first, and the new growth seems fine.
however your leaves are lime green(early stage N deficiency) and they are probably yellowing/dieing at the lowest oldest growth(mid stage), yellowing from the tips inwards, and its climbing up the plant(late stage).
you also have a major K deficiency; i bet money that all the leaves tips are singed(early K deficiency), now they are starting to yellow slowly and that singed tip is area is getting larger(mid stage), and finally those rust spots start appearing and that the late stage. heres some pics so theres no question
N deficiency early, notice the lime green
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healthy plant, notice leaf size and color
and the K deficiency pic
the best quick guide pic ever
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