OK keep this in mind ....if you did nothing different to your plants and this is happening .....its probaly ok ....aslong as its not half the plant . A very important thing to keep in mind is ....if the growing tips of all your soon to be colas are GROWING,GREEN,NOT UNNATURALY TWISTED,NOT BURNING,NOT WILTED........BE COOL....wait it out a little plants do change....them droping leaves and turning a little yellow at bottom when flowering is like a man hair going gray ...its just a process in life....but not the same with every plant though .