what's wrong with these ladies

They look a bit over fertilized overall, but nothing is wrong with the plant. It's pulling the sugars stored in the leaves and using right now so the leaves die off. It's common about this time in the flower cycle of the plant so no worries. As far as the nitrogen toxicity, you need to back off the nutes (or should've already). I would definitely do a flush before harvest if it were me to get some of the nutrients out before you cure it. A healthy MJ plant is that nice deep blue green we all love. Too green...too much nitrogen. If it starts to yellow....it's hungry and needs fed. Nutes are nothing more than plant food and if you're going to use them a lot, you need to read up on the whole thing and know what you should give during the different stages of the plant. But it's just plant food. LIGHT is the "gotta have" if you want big plants and fat dense buds. No matter how many chemicals you pour in the container, it will only grow as much as the lighting you have in place forces it to. We're attempting to mimic the sun with the indoor grow and we have nothing that will even remotely come close, so overkill is necessary (per plant) with the artificial grow. Each plant needs super good wattage in the correct spectrum for cycle your plant is currently in and plenty of space to spread during flower so that great light can penetrate the canopy of the plant and develop out the buds down inside. That is how you get the most out of a MJ plant. Keeping light and plant as close as possible during flower is going to increase your yield too as long as you don't risk light burn.

Most people don't have any concept, until they've grown for a bit, of just how much lighting it takes for each plant to actually get a good harvest out of it and heavily overload the light they do have. If you have to raise the light higher just to cover all the plants you're running, you do not have enough light. The further away the plant is from the light, the less good you get out of it and the plants will only stretch to get to it. You don't want your plant spending it's flowering cycle stretching for light....you want it working on filling out buds. So you actually get a better return by flowering less plants and giving those you do flower the most awesome conditions possible. If you only have enough light to flower a single plant, you'll be much better of doing just one. But like I said, once you run a few through, you realize that it's not the nutes that get results. It's lighting.

 

I don't claim to be an expert in diagnosing plant problems, but I would say you have way more problems than nute burn. That discoloration of your leaves and the necrosis is not normal and indicates a problem. Obviously flowering has been affected because the buds are very small for 7 weeks in. Here's a comparison - 7 weeks. No leaf discoloration.

 

What size containers do you have them, and what are you using for media? Looks like a really fast sativa!

 

i think your plants are probably rootbound. They really don't look bad. Cure those ladies right and enjoy