Probably in flower. Drought, UV light.
I wouldn't worry about it. I don't stress my plants. Give them only the light they need. Don't push the plants much and my plants are always potent enough. Genetics are probably the most important aspect. By stressing the plant you are more likely to do damage.
I hear what you are saying and it makes good sense too. If the genetics are strong enough for your liking then yes, why the hell bother, you'll probably only stuff if up and cause them to hermie or whatever. I agree with all that, especially for those growers who are only growing one plant and can't afford to risk stuff ups. However, for those folk who can afford to experiment because they have space to run plants on the side differently, then in those cases why not.
I have experience in this, altho it was nothing planned, purely circumstances and luck, but the result intrigued me so much I often played it back in my mind to try and understand what happened. Now, I feel I understand, and it was due to inadvertent drought stress. Of course I think any successful grow needs a few key things, sunshine, temperature, nutrients and water. It was an outdoor grow on my balcony which I didn't start until nearly the second week of Summer, so a late grow in good bag soil, which was only ever given 2 feedings of tomato food, that was all the additional nutrients it ever got. So nutrient wise it was deficient but I probably got away with it because it was a late and thus short grow. The pot was heavy ceramic maybe 15-18 liters that heated up in the sun. The balcony location has stone tiles where in summer the radiant temperature reaches the mid 30C's (or the 90F's). I'd water every day, and every hot summer day by the end it's leaves would be wilting.
The resulting bud upon harvest was airy, something I read could be caused by too much heat. I think now, after having a few more grows in experience, that probably the airy bud was also down to nutritionally spartan soil. However, although the buds and sugar leaves were 'airy',
it was like the sugar leaves and bud growth had been coated in shellac, they were stiff and rigid, as if they'd been given a coat or two of varnish. It is worth pointing out that the genetics were unknown, it was bag seed, and the bag of weed it was found in was nothing special, yet the resulting dried and cured bud was exceptional, it was noticeably stronger than 'average', and experienced friends who I gave samples to were likewise very impressed. I felt at the time that the plant must have caused itself to become more sticky/oily to protect itself from the heat and water shortage it experienced, I think now that is what happened, it was a beginner's grow and all down to pure circumstance.
So to recap, I fully agree it's best to aim to keep your plants happy and not stressed. But for those who have the inclination and capacity to experiment, that was my experience of inadvertent drought stressing. On my current grow I have endeavored to keep my 3 plants happy and not stressed, but now I am only 2 - 3 weeks away from harvest I intend to 'ration down' the waterings just to see how it goes, I feel the bud growth so far is probably mostly there, it would be interesting as per the Caplan research whether it can cause a THCa lift. Of course this is just purely subjective, but as my yield this season looks to be greater than I expected I might as well give it a go!
Just for shits and giggles, I'll post a pic of an inadvertent 'dehydration event' that my girls were subjected to just before the New Year when they had no water for 8 days. I think controlled drought stress to raise THCa probably works best in mid/late flowering. Note please, this was unplanned so don't try this at home! A pic of the same girl taken yesterday follows.
keep safe and well everyone!
And the same girl taken yesterday
