[Arid_gardener] Question from Home-Hort WWW page

[vicgelati at hotmail.com]

Vicky
85255
vicgelati at hotmail.com

We have several 4-foot tall Totem Pole Cacti (lophocereus schottii forma monstrosus) in our back yard that have been very healthy since they were planted 2 years ago.  In the last week we noticed that two of the Totem Poles have turned black at the base of their "trunks" -- this is the section just above the soil level.  The remaining parts of these two cacti look fine.  

Do you know what could be causing the base to turn black?  What can we do to solve the problem and ensure the health of these Totem Poles?

Thanks so much for your advice -- we really appreciate it.