Hey mate! :smoke: This looks like combo Ca-Mg defc.,... LOL!- there's a reason they pair these two together, as one is often linked/followed by the other,... yeah, some of the necrotic damage does look a bit like P defc., but the leaf color is the tell (yellowing pattern), as is the spotty nature of the necrosis; P defc. usually causes patches of wasting/necrotic tissue, even when still fairly green at times! Also, Ca is very poorly mobile, so uppermost growth tends to be hit the hardest, while Mg is fully mobile, and will be drawn off lower fans first, yellowing them out from edges in, usually w/o spotting .... Ca-Mg munchies are not uncommon; had one plant that ate 3 times what the other seed-mate had, and at this stage, it's almost automatic! no doubt, the most common defc. syndrome I see here,... I have no idea why this happens though,... :dunno: regardless, this is not damage caused by fungus gnat larvae attacking the roots, in epic numbers... you would know by the clouds of adults flying around, and the maggot-like larvae that might be at the bottom of the pot drainage....symptoms simply don't match up...
...do you have a dedicated Ca-Mg supp'? the conc. of stuff in them is usually high, better that molasses; Foliar is out at this stage of budding, barring a desperate severe save attempt,.. but you're not there! If not, molasses will do in a pinch, as it has decent amounts of Ca, Mg and K in it, plus the sugars will make the soil herd and plant happy; mix at 1T/gal soil drench; make sure to quit at least 10 days before projected harvest, as part of the final cleansing process,....
(Do you have some gnats? Small numbers are no more than a nuisance, but no need to put up with them at all; nothing kicks their asses like Mosquito dunks, or the bacterial equivalent,...(that's how they work, there's a specific bacteria inoculated in them, that gets in the bugs' guts and wrecks them)... I found granular stuff at OSH, instead of the pucks that are a PITA to break down!
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