Help! My Trichocereus bridgesii monstrose are in trouble!

Tucson, AZ

Hi all,

I bought several of these as investment. It's so rare to see them and they'll fetch a few dollars on Ebay :-). Now I'm worried my investment is all going down the tubes. In the past week or so, several of the plants have developed pinhead to 1/8 inch size brown or black spots. The spots are raised and hard. Strangely, it seems to be mostly on the older growth. Insects, fungus? There's no sign of spider mites or mealy bugs, cacti and succulents worst nemesis. I don't know what to do. I'll be taking cuttings of unaffected growth off all the affected plants. And I've quarantined all of them. Any ideas.


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Prairieville, LA(Zone 9a)

Hi Dave.

I did some searching around and came up with a few suggestions (anecdotal)

One is injury, either by the spines poking the plant when moved or from insects.

Another was fungal infection occurring after insect/mechanical injury

And a third was suggested as reaction to change in temperature/water regimen....too much sun and too much water...then a sudden change to less of each.

Perhaps you may want to use a systemic fungicide as a preventive measure

Decatur, GA


Mesa, AZ(Zone 9b)

Hi franj,

In the middle picture on the 'arm' in the upper right it looks like there are some non-black spots that look like the 'suck' marks of some kind of bug. Looks like the black spots could be scarring of similar spots? So some kind of bug?

I have a couple of San Pedro cacti that show similar little spots, but slightly lighter and only on the sun side so I have always attributed those to some kind of sun related reaction. But I have also had some plant bugs come through that like to suck on cacti and leave spots that are very similar looking to those in the upper right of the middle picture.

Tucson, AZ

Thanks for your replies. It may have been started by a bug but as "themoonhowl" suggested it may be a fungus spread by the bug. Here's a pic of an affected stem I cut off and quarantined a day ago. Whatever it is has spread like wildfire. I'm afraid it's going to be a total loss, as no systemic can possibly work fast enough and all plants are affected to a degree. I've treated with fungicide, let's see what happens.

I hate bugs!


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