Cactus problem

This was a beautiful golden barrel cactus yesterday, belonging to my neighbor. She went out to water today, and this is what she found. I can't believe our Phsycotic weather had anything to do with it, as I've seen these in Anza Borrego State Park where the temps can change 70 degrees between night and day. These neighbors are NOT gardeners, and watering is not high on their priorities list. The 24" pot has drainage holes (I'm told), but the soil is Pretty peaty Is that the problem or there something else possibly going on?

Seeing all the grass thriving and the cactus dead leads me to think first of what conditions make the grass grow that cacti do not like.

Top of the list:
Poor draining soils are deadly to cacti, but weed grasses will tolerate a lot of bad drainage.

Secondary things:
Sunburn and especially freeze damage can look like this (brown mush). If it happened 'overnight' then I would tend to suspect freeze damage. Containers can freeze when plants in the ground are OK.

But really, I am betting the first item is the problem.
Poor draining soil. It does not happen overnight, though. Takes a while before the cactus dies of too much water.
If you unpot it and smell the soil you might notice that it has gone bad (it may not reach this point before the cactus dies), and you can probably make a good estimate of whether it drains well enough or not.

Thank you, Diana. That was my guess also, but I'm not familiar with cactus diseases, if there are any, so I wanted a second opinion.

The worst problem for almost all cacti and succulents is lack of oxygen around the roots.
Water in the soil excludes oxygen.
Low oxygen levels lead to many kinds of rot, usually fungi. Some of these invade the tissues and stop the plant from sending water and nutrients up and down. This can happen to any plant, but plants that evolved in really dry areas are much more susceptible to this problem.

The only way to get oxygen into the soil on a regular basis is to allow the soil to drain properly, and not water too frequently.
If the soil is mostly coarse material that does not hold water very well (like sand) this is much better for plant that need such excellent drainage. Does not have to be pure sand. I would mix potting soil or compost with coarse sand for cacti and succulents.

The other problem (also true for all plants) is growing them where it gets too cold, too fast. If the temperature drops slowly, each night is just a few degrees cooler, then the plants adjust and can survive quite cold weather. But if the same cold comes on suddenly without the gradual chilling over several weeks, then plants can freeze that normally would not have had a problem.

It's very unlikely that temperatures in Santa Ana were cold enough over the past few months to cause the problems.

I do agree with you about the drainage problems.

Santa Ana as well as the greater Los Angeles area did experience very heavy rains in early March I think. It's very possible that the cacti were subjected to this rain fall without proper drainage. It has taken several weeks for the results to be visible.

I have several cacti. The only times I've had problems is when they were inadvertently watered each time the automatic sprinklers came on for the rest of the yard. Fortunately I noticed the problems soon enough to repot them and move them to a spot where I had better control over when they were watered.

Look at this site at http://cactiguide.com/cactipests/. It lists the various types of problems and pests that effect cacti and how to solve them.

Thanks for the link, Shorty. We got less than 2" out of that storm system, but that plant was NOT in a cactus mix. To make matters worse she was digging around with a trowel, trying to get the grass out and probably damaged the roots. Last time I looked at it there were no signs of scale or mealies, but there could have been pathogens of some kind in the soil. It's a shame as it was a nice sized barrel.