Looks like youre about 3ish weeks into flower. By the slightly burned leaf tips it appears that youre feeding a tad more than what might be needed, but now biggy.
But the leaf in your hand shows some deficiency. Im not experienced enough to know exactly what...maybe somebody else can chime in on that.
But... at this stage it is not unusual to see some yellowing/necrosis. The girls are using a lot of energy pushing out the bud. Nothing to be alarmed about.
Are you using bloom nutes yet? They need more p and k now...