Scale insect. Start cleaning . NOW!My own 2 pachycereus marginatus caught it, and one died. The other lives and is pest free...

Clean very very thoroughly and cover with protective pesticide/insecticide..

Your cactus is infested with scale. Get some rubbing alcohol I use 91% or 99%. Spray the cactus and use a soft toothbrush to dislodge the pests, and then wipe them off. Focus on areas where they can hide like the areoles. You will need to do this once a week for about a month. Each time there will be less and less, but one treatment won’t cut it. In a month I would personally repot and give new fresh mix and a clean pot. Some people use neem oil, but I’m not a huge fan of he smell.

Quarantine because scale spreads. Keep the cactus out of direct sun during treatment, neem oil or rubbing alcohol and sun will burn the cactus.

Lastly, keep a close on your cactus so you can catch the scale early so they don’t get so out of hand. Goodluck:).

I think that is a type of small scale infestation. That is a lot of scale. I've seen this kind of scale on Stenocereus marginatus a few times. I've not had much experience treating it. Just Googling about treating scale I read some suggestions to use neem oil but I've read some people have problems with oily residues remaining on cacti. If it were mine I'd probably start by cotton swabbing or q-tipping off as much scale as I can with 70% isopropyl alchohol. Let it dry. Then I'd probably use a few applications of insecticidal soap or a topical pesticide spread out over a month to kill anything remaining. A topical pesticide containing a pyrethrin would probably be enough. The skin of the tip of your cactus might scar because of damage from the scale.

Edit: Same thing on this cactus https://cactusjungle.com/wp-content/uploads/2011/02/scale_on_a_cactus.jpg

Looks like a heavy infestation of scale.

Could it be a SEVERE case of scale? Try wetting a cotton swab, cotton ball or paper towel generously with isopropyl alcohol and rubbing your plant with it. If it’s scale it should come off. Be sure to keep your plant out of direct sunlight while treating and until it dries.

These little critters will spread from plant to plant. I perform a daily critter hunt but even with that I missed a couple of my plants that had a minor case of scale getting started. I treated them as mentioned above and it came off pretty easily, but it’s an ongoing battle and I will have to be vigilant in monitoring and retreat as scale is difficult to eradicate once it’s gotten a foothold.

If what your plant has is indeed scale I’ve never seen such a severe infestation. If this is not one of your favorite plants it might be best to dispose of it to prevent further infestation of the rest of your collection and be sure to inspect your other plants as well.

I could be wrong though. Wait for others to chime in with their opinions and advice before tossing.

Tyler

When I put up my comment last night there was no ther comments before mine, but when I look now I can see them all, and Jeff had posted as early as 4 hrs before me. I’m guessing everyone else saw the same as I did last night.

I saw the same as you, Kara. I thought I was the first to reply.

I cannot thank all of you enough!!

I will try to save my spiky friend and send a photo if successful :)

I saw it this morning around 5am. No other posts and thought I was the first one. Each time I refreshed it still said zero comments even though I knew I had just posted and could see mine there even a few hours later.

Yet another HOUZZ SNAFU! AWESOME!

Tyler, if we're going to be SNAFU'd, I'm glad it's with you. I thought I was the first poster when I posted it, but then went back to the main page twice; each time the 'be the first to comment' siren beckoned, but when I went to this post my comment was there.

It all starts with the ridiculous spelling the owner uses for 'house'. I guess that's not going to change, so

'Nothing but SNAFUs do I see'

(sung to the tune of 'Blue Skies')

Hey Jeff, I’m curious as to the insecticide you mentioned above. What is it and why is it held in disfavor, please?

I've been howled at by the leading soil guru for advocating using Windex / Formula 409 to remove scale. Thing is, it works, as long as one follows a few simple steps.

...and what might those steps be...?

Just the usual when treating - keep out of sun, multiple treatments, alternating with blasting the scale off with the hose (it's wonderfully freeing, that feeling), and keeping out of the sun again for a day or so. Mr Guru claims that the chemicals in those solutions harm the epidermis of the plant, and I don't say that they don't, but at the same time, it doesn't seem to hurt the plant., and it's used by a number of cactus professionals, from whom I got the idea, and it's 100% effective in killing the scale. Fortunately, the plants needing treatment with such extreme prejudice were few.

Thank you Jeff. So when you say alternating you mean using Windex one day and then 409 the next time? Rinsing off in between, of course. How long do you leave them on before blasting? Any rubbing involved? Sounds like that would be ideal for getting into those tight spaces or in the areoles.

You know what else harms the epidermis of plants?

F***ing scale!

Tyler, sorry for not being specific. I meant alternating between solution application (of either, but not both, IME) and then water blast, for however many cycles of this you need (even heavily-scaled stuff like the OP's) - I'd just leave the solution on for 5 minutes or so, then reapply, wait a few minutes, then blast and repeat as needed. It is a distinct pleasure to watch the pest get peeled away from the plant by the carefully-applied water stream, let me tell you.

Kara, it is that simple, but I'm still glad I wasn't drinking anything when I read your comment.

Thank you Jeff. And Kara...well...that’s Kara for you!

So this isn’t one of the plants I was talking about having to treat but I just noticed this on my Stenocactus Multicostatus. Reminds me of the rust I used to see on some of my roses.

So rust or scale? What do you think, please? Treatment recommendations?

Thank you.

CRAP!!! Just discovered this HEAVY INFESTATION on my Rainbow Hedgehog! The spines are so thick I didn’t notice but then realized I couldn’t see ANY GREEN showing through on most of the plant! To confirm what I thought I was seeing I used a tool to scrape down the center of a couple of the mid-rib areas, visible in the 2nd image.

I have some Windex on hand so giving it a try!

...and 15 minutes later ALL CLEAN! Windex as a gardening tool! HA! Who knew! JEFF, that’s who! Thank you, Jeff!

I'm blushing, Tyler. Kills the epidermis, yet it works. What's a fellow to do with suspect knowledge but share it, eh?

As to your former, it looks like spider mite damage, or so I've heard. Have you posted on the pests/diseases forum here?

I haven’t posted there but will try that. This plant lives on my very crowded succy table. Spider mites would decimate the greater part of my collection so hoping that’s not what this is. I’ve seen no evidence of spider mites and keeping my fingers crossed!

I don't think that's what it is, Tyler, but what it was. Literally. They're not there anymore, but they were.

Counterpoint - I'm all wet about the cause of that damage. At least it's just visual and not mortal, IMO.

Thanks Jeff. I am soooo hoping you’re right. Bad enough that it’s scarred without having to battle spider mites. I just wonder when they visited me. I swear I’m out inspecting every day. Sometimes multiple times a day in different light. I thought I was being anal but apparently not.

I posted to the Integrated Pest forum and the Australia Pest forum. I’ll let you know. I tried to select both forums at the same time but when I was finished posting, the Australia Pest forum disappeared so I had to post it again to that one separately.

You don't know about the Australian Pest forum posting rules? You have to type from right to left for it to take.