I would not sweat the yellowing lower leaves that late in flower. You don't need any kind of nitrogen boost this late in flower. A much bigger concern would be the spider mites. Have you treated the plants with anything yet? I am going to tag
@JL2G so he can chime in here on the mites and possible treatments. He is a good soil man and might be able to help. I have yet to battle them but prepared just in case. One thing i have on hand is Dr. Earth Final Stop which can be used late in flower. I know they can multiply scary fast.
Thank you!! I pulled that plant and have been very thorough checking other plants and they have no signs like the infested plant did. I was told dont bring them in and I should of listened. I have not done any bug treatment on any plants I now see why I should on out door and possibly sterilize soil. I used dr earth and had no problems. Bought promix used with seedlings and hello fungus nats. I'm hoping the spider mites didnt spread. Plant was maybe 2 feet away and air blowed away from the others. Also no ants to carry them or anything so I'm hoping.
I hate bugs. Lol.
If there were, or are bug signs, especially mites, I'd personally I'd go all out on some IPM before they have a chance to possibly multiply.
They hide very well.
Just because they aren't seen doesn't mean they're not there still.
I go with captain jacks dead bug spinosad powder for dusting the soil and pots with.
Can also dust the plants too. It has DE in it as well so a double punch application.
For sprays I add horticultural oil, a bit of neem, and some dawn dish soap. H oil, which is mineral oil, it will melt egg sacs and suffocate live ones of most bugs. Neem gets em too, and dawn is the surfactant to help it all mix up good as well as an IPM. That Dr earth final stop is another one I use. It's just a mix of essential oils that take out bugs.
Yrs ago outdoors I had a bout with spider mites and 3 applications about 5 days apart each, on the plants with the Dr earth final stop took care of it. I also sprayed the entire yard around the greenhouse as well.
Sure don't wanna let em get a foot hold in the door. Lol.