I am in S. TX and my plants are 2 years old. They are -probably- 7 ft. tall and very leggy. A week or so ago the bottom branches started turning brown. Browning kept going till 3/4 of plant died. To me, it looks like a chemical defoliant of some kind. I have removed all brown leaves and plan on cutting off small branches that are clearly dead. They are unsightly but are really making an effort to produce flowers. Can I cut plants clear back? if so, how much should I leave? Also how short can branches that are alive be cut back?
You can actually prune back the entire plant in the early spring.
These articles will help you.