It's always best to include as much info about the situation you are in, when asking for a diagnosis. My first guess (that's all you'll get are guesses without info) is rootbound and/or ph issues.

The link to the troubleshooting form is in my signature, below. Copy-n-paste the proper form here, answer all you can.
Rusty Trichome Reviewed by Rusty Trichome on . need help to id problem (pics) I am sure they are not over watered, Could it be heat stress?Ph is good,Not over fert. Leaves are droppy and canoing down. the problem is limited to just a few . Rating: 5