Is there anything wrong with my Pachycereus pringlei?

[friedrich03]

I noticed some black markings that where not there before. What is it? Is it something I should be concern about?

[Brunãozinho]

I think you should be concerned about that, hard to tell what that is... is it just on the top? is the plant showing any signs of growing (fresh spines on the top for example)?

[friedrich03]

Yes just on that little area shown. Other than that, the plant seems to be ok.

[Brunãozinho]

I thought it should be rotting, but normally the whole plant would soon be showing signs of rot, not only the top of it. If it's a fungal infection that affected the whole upper part of the plant than it could spread to the base too, and it would be best to cut it off... but then you would have to be sure of what it is.

[greenknight]

There are several species of fungi that cause a dry black rot, doesn't spread quickly. However, that generally starts as a spot which slowly expands - the way it's developed on the edge of the ribs on this plant looks more like severe sunburn. Did you move it into a more exposed location? Is it getting reflected sun off the wall behind it, as well as direct sun?

In any case, if it's not soft and mushy you don't have to worry about it spreading quickly. If it is soft, you need to do surgery on it right away, but if it's hard and dry you can take your time figuring it out.

[friedrich03]

I poked it with a toothpick and it felt hard and dry. So far it's the only area that I noticed with the black marking and it hasn't grown or spread to other areas. It gets direct sunlight every morning. My patio is facing east.

[greenknight]

If it is fungal, you should see minute fruiting bodies at some point.

It should be safe to wait and see. Fungi that produce symptoms like that are more of a threat to seedlings. Older cacti usually are infected only through wounds, and they are able to wall off the infection and stop its spread.

Not a plant that should sunburn easily, don't know what to make of that.

[friedrich03]

If it was rot or fungus, how long does it usually take for me to see it spread to other areas of the plant?

[friedrich03]

A closer look at the damaged area.

[greenknight]

If it was rot or fungus, how long does it usually take for me to see it spread to other areas of the plant?

Since it's not soft, it might not spread at all; cacti can live for years with black, dead patches of dry rot.

Not sure that's what it is, I don't see any sign of fruiting bodies in that closeup. The only thing I'm sure about is that it's going to look bad forever, and the only way to get rid of it is cut it off.

Are there still new spines growing out of the tip bud? The growth point is still alive, it should grow past this and the spots might not be very noticeable after a few years. If the tip is dead, you might as well cut it off because it's topped already.