youll get more help if you list your growing setup and conditions. A whole shot of the plant might help, but a whole idea of your setup will help more. Good luck
that looks nasty , but stated above we need your growing conditions.
hydro?
ph?
waterings?
nutes?
stage of plant?
heat? etc... and a full shot would help better
looking into that more reveals that it is very rare and is in most ferts... what would you do to fix that? And please dont say get some boron because I know you can easily over fert with that shit..