Trying to figure out what is going on here. Only 2 out of 3 plants have this problem. The worst is my blueberry.
I agree with @jetlag. Cal-mag def. possibly a bit of over fert.
Have you checked the ph and ppm of your runoff ?
The only thing I have given recently was Fish emulsion. I haven’t checked runoff.
Looking at other topics it may be Nute Burn. Checking pictures it looks similar.
Might be a bit of phosphorus deficiency as well. I would start some bloom nutrients.
Is it just at the top, or all the way through the canopy?
One plant only on the top the other half way down
I not an expert, but from my experience… when the nutrient deficiencies show up at the top of the plant it is related to the intensity of the light. Brighter lights increase the demands for nutrients and any deficiency shows up first where the lights are the brightest.
I ran an experiment this summer where I really pushed the lights. It created what I perceived as a calcium (mostly) and magnesium (to a lesser degree) deficiency so I started treating them and most importantly, I decreased the intensity of the lights. Of course the damage was done and the leaves never recovered but it seemed to stop the progression.
I’ve had the light on 24/7 since I started them. I just cut back to 18/6 . This is my first grow. I’m surprised how easy . Only have to last a few more weeks.