You've got an insect problem and just because you don't see it on the other plants doesn't mean it's not going to start happening there, too... Whatever the insect (and precisely WHICH insect doesn't matter!), it's almost literally sucking out the life of your plant and you need to deal with it before it kills the plant completely. Get some Dr. Zymes Eliminator or some Spinosad and use as directed, spraying just before lights out. Spray ALL of the plants... top and bottom of all leaves... both products are organic and can be used all the way up to the day of harvest without damaging either the flowers or the taste of your smoke...
Good luck....