Question
Hi,

I recently purchased a large San Pedro cactus and within two weeks it has gone from a happy healthy plant to a yellow spotted plant with dried up white crusted areas (located in the center of some of many of the spots. There is also a small amount of white webbing between the columns that are located close together. What can I do to save this plant? The problem is spreading at an alarming rate.

Thanks,
Claire

Answer
Dear Claire,

It is hard to say without seeing a picture, but it sounds like a couple of things are going on. Possibly root rot and an infestation of mealy bugs. Take a look at this webpage: http://www.succulents.co.za/succulent-plant-pests/mealy-bug.php

Also, if you have it in direct sunlight, you'll need to move it out of the direct sun ASAP. Most people assume that cacti originate in the desert so they can take full sun. That is true, but only if it was raised in direct sun. If it was grown in a green house, it is not acclimated to direct sunlight. If it was raised in direct sun, then the plant must be oriented exactly like it was at the nursery. The reason is that the south side of the plant developed a thicker skin. If you reverse that, the plant will sunburn and die.  

If you can send a picture, please send it to: [email protected].

Sincerely,

Greg