I have spotted what I think is your problem. First, definitely pay attention to the FoxFarms chart and stop guessing at 1tsp per half gallon. Use the appropriate nutes for the age of your plants in the correct amounts and definitely adjust the ph to 6.3-6.8 BEFORE you pour it into the soil.

But here is the reason for your rust spots I think. I am betting that you are root bound. That plant looks awfully big for that pot.
emilya Reviewed by emilya on . need help with my plants ASAP plz! i have a white widow x big bud and liberty haze that is a month old they getting rust spots and dying leaf tip/ ridges on them and im not sure what the problem is.. im using fox farm OF soil and the fox farm trio nutes ph'd at 6.8...im only putting 1tsp to every half gal.. i have a 400watt MH about 2 foot above the plants ...air circulation temps range from 77- 84 f... 24/7 light ...i included some pics of the WWxBB if you could please help me b4 the plant goes to hell...THANK YOU Rating: 5