My girls are in their 7th week of flowering and have suddenly become more sensitive to the HPS light. They stopped stretching weeks ago, so the bulb distance hasn't changed, but the leaves that are directly beneath the bulb have started yellowing while everything else looks great. The closest cola is 20" from the 1000W bulb with ample air movement, but even leaves that are nearly 30" away are yellowing. I've been going very light on the nutrients (half the recommended concentration), and I'm wondering if the intense light combined with a nutrient deficiency could be causing the problem. I'll post some pics tonight under normal lighting. Any thoughts?
I found a good old post recently
https://www.rollitup.org/marijuana-plant-problems/304649-marijuana-deficiency-table-report.html
According to it affecting the top portion of the plant could be one of these
10. (a) Leaves are yellow or white, but the veins are mostly green. >> Iron (Fe) deficiency.
(b) If not, #11.
11. (a) Leaves are light green or yellow beginning at the base, while the leaf
margins remain green. Necrotic spots may be between veins. Leaves are not twisted. >> Manganese (Mn) deficiency.
(b) If not, #12.
12. (a) Leaves are twisted. Otherwise, pretty much like #11. >> Zinc (Zn)
deficiency.
b) If not, #13.
13. (a) Leaves twist, then turn brown or die. >> The lights are too close to the plant. Rarely, a Calcium (Ca) or Boron (B) deficiency.
b) If not… You may just have a weak plant.
