I read in your other post that you had fungus gnats earlier on.
I've had those, too, and it took a while for the plant to regrow the roots back that were damaged.
You have to understand that the life cycle of the fungus gnat means that while the fliers are dead and even a lot of the maggots during the first treatment, the eggs still hatch and immediately start eating the roots again in 3-4 days.
It takes repeat treatments to keep killing them offspring. I'd recommend a watering with 1 part hydrogen peroxide to 4 parts water to kill them for realz if your infestation was that bad.
It oxygenates the soil, too, which is good, but it also kills a lot of flora and beneficial microbes.
Don't worry though, you'll still see an immediate growth spurt. The mangled leaves you are seeing start at the roots directly affected.
Plants have veins that carry liquid up and they really are all mapped out to specific areas as they grow. As the grubs finish the fungus off, they go right to the roots.
If it were just a handful of leaves like what I had going on, I'd say sit back and let the plant regrow new roots and wait.
Since your case is obviously advanced, you should probably hit it with the nuclear option, in my humble opinion.
Flush with the peroxide water and you'll see new and healthy growth in a matter of days. The mangled stuff won't spring back, I'm afraid.
I have a handful of plants that are working their way back to vitality once again, but I've only done one treatment of Monterrey Bug Buster O to the cedar mulch soaking the top layer of soil and as a foliate spray. I will be hitting them again tomorrow evening after the sun goes down, too.
Ain't nobody got time for mooching fungus gnat babies all wrecking my plants' ability to take in nutes.
If you can't find Monterrey Bug Buster O, or the infestation is bad like yours was, nuke them dead with peroxide and water. 1:4, no more.
I am relatively new to growing cannabis but I have experience with fungus gnats. I inherited two giant and beautiful houseplants form someone in town and immediately began noticing little flies everywhere. Well, I found them around the pot of the jade tree and a lightbulb went off. I tapped the top of the soil and a bunch of flies came out!
I found the peroxide trick online, and it was being recommended for someone's cannabis. I figured if it was safe enough for cannabis, it was safe enough for the jade and the Norfolk Island pine I had growing.
I had tried sticky traps, no luck. Tried little bowls with vinegar and soap/water mixture -got a lot of flies but it didn't stop them.
Tried the peroxide and they've been gone ever since! One good watering of it and that was that. Eggs, maggots, larvae and flies gone.
I'm a believer in it for sure. All it took was letting the soil dry out a bit and then a feeding of guano/fish emulsion and both plants immediately started thriving.
It was so quick.
Cannabis is even stronger at recovery than these two, and during the vegetative stage it's all ramped up to grow as quickly as it can. Be glad this didn't happen while flowering!
With my outdoor crop of cannabis currently growing, I didn't have peroxide, and the closest hardware store didn't either. What they did have was Monterrey Bug Buster O so I tried it. So far, no flies, but repeat treatments are necessary.
Pyrethrum doesn't harm cannabis, and as long as you flush after their dead, they'll be fine.
Next time you get a grow going, set a sticky trap out right away and keep and eye out.
They're so much easier to kill with pyrethrum when the infestation isn't that bad.
The problem is that the poison has to make physical contact with the bugs to work.
If I were you, I'd do a foliate spray and the peroxide, or you will have to just toss the whole batch of plants. They won't yield much any way if they stay infested. They may not even live through their whole life cycle.
Good luck, dude. Hope some of this helps, from a noob to a noob.
Well, an old noob that has a few tricks up his sleeve.