If it is rust, it will rub onto your fingers…else looks like it is a burn from either nutrients / solution dripping on the leaves, phosphorous issue or even burn from misting with lights on / too close
Good morning! I looked up previous answers for this type of problem, and all answers seem to point at a phosphorus deficiency. Does that seem right for the spots that are appearing only on this one Bruce Banner auto? It is 7 weeks old, in FFO mixed with Happy Frog. I only water every other day with a mixture of 1 tsp. Liquid kelp & 1 tsp. Earth Juice Hi-Brix molasses to a gallon of water. Lights are 18/6 at correct distance. Thanks for any responses 
Applied neem oil on plants kindla heavy on top and bottom. Next morning they looked a little pissed. Now today they be so happy. Thanks for all da info .
@Kris there’s no purple on the main stem just the leaf stems and this late in flower it’s likely just the fall fade as nitrogen in the plant is being used up.
The thing I’m concerned about though is the spots on the upper foliage. It shows there’s an immobile nutrient issue. It’s likely cal-mag by the looks of it. Start adding some cal mag to your waterings and it should fade as normal and those spots will stop forming.
When I said it looked like rust I meant the color, not the disease.
Thank you! I didn’t know to look for purple on the main stem as an indicator. So much to learn!
The spots are something I was very concerned about. Cal-mag is something I’m not familiar with at all. I ordered some this morning…thank goodness for Amazon Prime, only two day delivery time. Do I add this to my molasses/kelp mixture, or just do watering with the cal-mag mixed with water for a while?
Thanks so much for taking the time to share your knowledge
Yes add it to your water, follow the manufacturer’s directions or if you have a ppm/ec pen, your base water, before any nutrients etc added, just water and cal mag should read around 300 ec maybe as high as 400 if they are really lacking.