Question
how to remedy or prevent

Answer
Peter:

Several things can cause this to happen, and not all of them are infectious diseases. I would need more information on the specifics. What kind of plant are you having this problem on? Are just individual branches turning brown or large areas of the entire plant? Examine the plant in the trunk region- looking for damaged bark or injury. Check the individual branches for injury also. Anything been applied or sprayed on the plant?

One option for you to consider is to snip off an affected branch and carry to your local nursery to get their opinion.  Many times they may have seen something similiar.  It will be very important for someone to see an actually physical sample to give you a better diagnosis.

Regards
Steve