You silly boy.
Now thats out of the way you have spidermites because you bought a dope plant into your clean uncontaminated growroom from 'somewhere' outside the room.
Spider mites from another grow room are very hard to get rid of as they are immune to many treatments already and are survivors...
If they are close to harvest I don't want to flush and deprive them of nutes
A flush will only improve the health of the plant ,she will love it. Plants dont need as much nutes at this stage.
Its nute burn so your adding a little too much and you need to fix this before flowering. It could be that strain is sensitive to the nutes/medium you have. Maybe try canna terra.
This pathogen soup is the reason the plants look like crap and are dead or dying. Get some H202 35% grade + in there every 4 days to control this mess .
I think those pots are big enough for these skinny girls you have here. Also why is the bud so leafy and the the plant so leafless? What strain is it bro ?
No but under watering does , when the pot is allowed to dry to much too often salts build in there and stress the root system leading to salt burn, leaf drop and N lockout. You should be concerned. The damage is done now remember this next grow. Also try a better medium.
Its K def and you should have added some potash or flowering nutes by now. Sprinkle some potash around the drip zone and some super phosphate but dont over do it. When flowering starts plants are very hungry for K.
Bad nute burn, how old are these scraggly looking things? you need to change medium as the mix you have put together does not work for dope. I would start again if i were you because you could be flogging a dead horse here, it takes a long time to recover if ever, in the mean time you could be...
Vacuum sealed and put in this drum/container that has been dug into the ground . Find a sandy soil area that has no logging and very few fires. Large opening at top to get stuff in and out easier, GPS the location on paper then to a well encrypted usb then burn the paper.