The white "powder" is probably from the sole trying to slough off. Thrush is usually indicated by dark, soft areas on and around the frog. Treatment will help, but you may need a farrier/trimmer to come out and clean it up initially for you.
Until you can get someone out, be sure to clean and scrub the feet well. Use dish soap and water with a stiff dollar store brush to clean well. Dry and then apply thrush treatment (thrushbuster, thrush-x, etc) or your own mix of zinc and triple anti-biotic ointment (50/50 mix).
After the trim, you will need to maintain treatments for a while. Ask your farrier when (s)he comes out.