Nitrogen toxicity? - 39 days old, 65F, 60RH, sativa dominant autoflower, 10L soil pot

Yes, nitrogen toxicity. You should be getting run off every time you irrigate, it helps prevent nutrient salts building up in the substrate ans causing burning. Having a diary helps immensely when it comes to questions and answers. Are ou growing in soil?? If so, a schedule of plain water/plain water/feed/plain water/plain water/feed works well and certainly do not feed every time you water. I would advise strongly against any sort of defoliation, there is absolutely no need to do so, especially on a plant this size. Bushy is good......... More leaves = more energy being made = more growth! Buds need the leaves to make the energy that they need to grow.

Early N tox sure, nothing crazy bad though. yellowing tips could be from burning or lockout of other nutrient because of to much N. I agree give regular water Ph'd, if it progress much further do heavy watering with less N and let that push out the extra in the medium.

Hey there, Yes you over fed here just a tiny bit, I would recommend only water at the correct ph for a few times before adding new nutrients to your soil,there is no need to flush or anything Just get a good dry/wet cycle going on and she will be pretty fine Happy growing 🌱✌️