I've never heard of them causing leaf curling.
My understanding is the curl results when the stomata on the underside of the leaves open wide. This increases the surface area of the bottom of the leaves, pushing them into a curl. It happens when the temperature is high, the humidity is low or both. The plant then transpires more to cool or moisten its leaves. A high transpiration rate isn't necessarily bad, though, because it can increase the growth rate of the plant. It's only likely to be a problem when excessive. This relates to vapor pressure deficit (VPD), which is a measure that combines temperature and humidity. VPD charts are available that provide VPD ranges for the life stages of the plant.
The plant is happy, I have no clue why the sugar leaves cup up like that. I'm not sure it's even a bad thing. I would just like to know what causes it.
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Trichomes on sugar leaves when, ill say standing room only, before a sugar leaf finishes growing can absolutely by the time its actually done growing cause the edges of the leaves to go a bit wavy and turn upward, and a lot of this does look like that. Tends to happen on plants with more, larger resin heads (indica dominant plants) that have been getting just a wee bit too much N in their mix (Slight N toxicity causes the dark, sometimes shiny, curled fan leaves he has on the plant as well as hardening the individual trichs/resin heads).
Not being a contrarian, just adding info i promise lol.
you do usually have some other things present along side the heat stress symptoms that i dont see going on here. Aside from that one bud site, but that already is kind of weird considering there is material just fine closer to the light. Youll also usually see bleaching on buds this far into flower before heat stress and curling leaves, or at least both together. If the entire environment was too warm it wouldn't be a localized issue. Looks like maybe some slight bleaching, but again, there is closer material doing just fine not even showing signs of heat stress.
You are indeed correct about the curl resulting from too much heat and the stomata opening. And how this creates an upward curl to the leaf edges though.
My advice, if temps light height and humidity are totally under control, would be back off on the feed a little bit, or even just the levels of N if its a multi part feed. if you grow this plant again as a clone, or if its a stabilized genetic youll come back to again, i would jot down that one likes just a touch less N then you are giving it right now. But as it sits is nothing to really worry about. As the issue is expressing itself though, i wouldn't think it to be heat stress.
Those tiny brown tips on the leaves aren't necessarily indicative of generalized over feeding at that level either per se. On this plant its probably leaning that way. But some plants do just have tiny brown tips on their leaf fingers later into flower regardless how you grow them or with what.
I also attached a picture of a purple cookies pheno i had that would curl its sugar leaf edges, but ONLY where there were trichomes and purple both. Wouldn't do it on the green leaf. No clue lol. She just curled the edges of her sugar leaves in some form or another somewhere on the plant every grow, not the best pic to show it, but i dont have many pics of her anymore these days. Sometimes her sugar leaves would twist in straight up spirals sticking out of the buds. Sometimes her sugar leaves would do exactly like the OP plant if i had just a little too much N going on in late flower. Never caused yeild or quality problems. I thought it was kinda cool looking.
