February 26, 2019
February 27, 2019
Probably just "corking", a natural aging phenomenon.
From the photo, with the plant on the right, it appears excessive, but doesn't look like a fungus to me. Even if it is, there is not much you can do except adjust the watering to an appropriate amount, and avoid sprinklers hitting on the stems.
By the way, there appears to be two different types planted next to each other, maybe two species of the genus Stenocereus. I'm not a cacti expert even though I grew up in Scottsdale with a horticulturist father who was on the board of the Desert Botanical Garden. If you want to get into it, you can visit that great resource or use the online cactiguide.com