bryannaarmstrong,
Can you provide a picture? That would help in identifying the problem.

Planto

cut it off back below all sign of decease and see if it will stop its progress . spray it with Draconil or bayer 3 in one stuff. I don't know what it is but I would treat it quickly like it was a bacterial infection or rot.

A photo is worth a thousand words. =)

Yes, doing what Mara says above may be prudent, until you figure out what it is.

Did you have a freeze (or frost) recently? And was it in a area where it is not protected (by wall, other plants, etc.)? To me, it sounds like a plant affected by a freeze. If this doesn't apply to your plant, then I don't know.