Question
Hi..I have recently purchased a Pachycereus Margintus.  At the time of purchase it seemed to be very healthy but within days of brining it home large grey areas have developed along the edges.  These grey areas are hard and seem to be very dry.  There are also spots that look like some king=d of fungus that is spreading very quickly.  I wish I had a picture to post.  

Answer
Phil,

The gray areas may be cold damage. The edges and the very top are the most sensitive to cold. The spots may be damage cause by insects. Question, is this plant planted outside? If it is, both problems could have the same cause. Cacti are very sensitive to sun exposure. Most have a "south side" which has a thicker skin. If a cactus is planted in direct sun with the "north side" facing south, then the plant will sunburn and may die.

Sorry, but without actually seeing the plant, I'm guessing at what the problem may be. Let me know if any of these may be the cause.

Sincerely,

Greg