Hello! I recently landscaped my entire front yard with succulents and cactus, and unfortunately two of my cactus (Mexican Fencepost and Pilosocereus pachycladus) started to show signs of having problems. I pulled them out and cleaned off the roots to get a better idea of the extent of the issue. I potted them in a cactus and succulent soil and provided minimal water (minus a day of rain). The pots are located where they get sun all day. When I removed them the soil seemed in decent shape, nothing I could see of concern and was fairly dry.

My question is how I should now treat what I believe is fungus...do I need to do surgery and cut off the roots/rot? Or maybe just pray with a fungicide and repot in new soil? Or maybe this isn't a fungus? Appreciate any suggestions or tips!

Thank you for your time in advance.

What was the problem that you saw?

Thanks for the response! Sorry, should have done a better job of describing that. Hopefully the attached pictures give a better depiction too.

The Pilosocereus there is some white discoloration and shrinkage around the edges or areoles. The Mexican Fencepost has some brown spots but it's not all the way down, just below the soil line when it was in the store container. There is no rot at the roots or base around the roots.

I don't think there's any cause for alarm. The dark spots at soil level in the first picture of the new set may or may not be something to be concerned about, depending on whether they get larger and/or become soft. So keep an eye on them, otherwise the rest looks within normal limits given the history. If someone else here disagrees, I hope they speak up.

Where are you located? Given these plants were in the ground, I'm assuming somewhere that winter cold is not a problem. Are they back in fast-draining soil? Were they in the sun before you got them? Assuming you're in the northern hemisphere and not in the tropics, it should be pretty hard to provide too much sun this time of year. Wait a week after potting them up, or putting them back in the ground, to water deeply for the first time. From there on out water deeply when the soil is dry at depth. And make sure they are potted up at the same level they were to start with, ie. with the same parts buried that were buried before and the same parts above ground that were above ground before.

It's generally a bad idea to dig up cacti when you're concerned about their health, unless you are looking for something specific associated with the roots. Every time you do that you damage the plant. Which may not be a big deal, especially if you wait to water, but why cause potential harm when you're already concerned about the health of your cacti. It's especially important to avoid doing this repeatedly. Others may disagree, this is just my own opinion based on personal experience. What's done is done, this advice just for future reference.

Newly installed plants often go through some changes, presumably related to transplant shock, in the weeks to months afterwards. I think that's probably what you've observed. Best to leave them alone, watch the water, and continue observing closely. I can try to give more specific advice about watering based on the location and whether you have chosen to keep these plants in pots or the ground.

I appreciate all your comments and tips!

I live in San Diego (more on the coastal side) and I've had these two cactus in pots for about a month. Both pots have been positioned to get as much sun as possible. I used cactus and succulent soil mix and have kept water to a minimum (since potting, I've watered once and we had one day of rain). I believe both plants were in the sun prior to purchasing.

Again, thanks for your help!

That was proper rain about a week ago, so I'd wait another week to water deeply. The sun sounds good. Weekly watering should be good beyond that point, unless there's rain, provided the pots are not overly large.

Cactus and succulent mixes do vary in composition, and what you've described could be good. But when in doubt with desert cacti, use something fast draining with about 50% rock. I like a mix of 50% pumice, 50% organic for most cacti, and our climate is nearly identical to yours. So if what you used is close to that figure, great. Otherwise be sure it drains fast. The more organic in the mix, the more water it will hold and the longer it will take to dry out.

Try to keep an eye on the weather forecast for the next couple of months, and if there's rain forecast around the time you would otherwise be watering, hold off on the watering and let nature take care of things.

How cold is it getting at night at the moment?

I would not water the Pilosocerei if it gets below 50 at night. Just as a precaution given that you have been digging them up and messing with their roots. Most Pilosocerei come from what is often described as a tropical desert - ie. it does not ever really get cold at night like most deserts do in winter, so they are incredibly frost sensitive and also not at all a fan of wet feet + cold, and cold is probably well above freezing. I lost my big potted plant a few years back by mistakenly watering right before a period of cool but not exceptionally cold night time temperatures.
Since yours are already experiencing a good amount of stress I would try and keep too much water stress off the list.