I agree with the others that the plant is over fed and has a salt build up.
There is a lot of mis information circulating about soil growing. The salt build up does not happen for growers that buy fresh soil each grow.
Soil does build up salts if reused and never leached of the buildup.
There is a simple test to find out. Water the plant slowly to runoff. Test the runoff E/C and compare it to the input E/C. You'll need an E/C or PPM meter. Test the runoff several times.
My bet is the runoff will be so high the meter will max out and give an over the limit reading.
When there is a salt build up the roots have trouble with water uptake and the soil needs to be leached.