CactiGuide.com

Scale? Mealies? of What?..Its been treated and it continues to progress. I had to use a knife edge to break the one off you see in the top view. Thanks Guys..
Mike M

Shouldn't be scale or mealybugs if it doesn't rub off, and probably not damage marks either since they're growing. I have a small echinocactus seedling with the same or a very similar condition, and nothing seems to stop it from advancing. Many people said that it's a fungus, but I did try some fungicides. It's still healthy and growing despite the spots. Sunburn maybe? Mine does have much bigger spots, and less of them.

If you peel one shell off there will be a small white worm under the cover then its scale . If not then IDK

I have/had a similar condition on a Cleistocactus winteri, although the spots were darker. I suspected scale, so I treated it twice with a contact insecticide. It didn't seem to work. I then tried to drown the scale, which also wasn't effective. I also set out beneficial insects. After that I applied a systemic insecticide. All this over a period of 2 years.
Looking at your pictures and the following posts, I now think it's perhaps a fungus. The plant seems to quite healthy at the moment. The conditions in which it occured were lack of airflow, high winter temperature and not enough sunlight.
Do have a place to quarantine it or will you toss it?

Hi Mike,

Ohugal makes a good point, but I'll mention that too much organic material in cactus mixes can sometimes lead to fungal problems. Some species tolerate a certain amount of organic stuff in the mix while others don't, and it depends on how much of it you have in the mix. It appears that you have tree bark in your mix, so I'm wondering if your "problem child" isn't tolerating it well. The best soil component for desert cacti is sandy loam with a bare minimum of organic material, although I don't know if you'll be able to find it -- good sandy loam seems awfully hard to come by here in the US. Too bad, because that will minimize the possibility of fungal attacks for pretty much all desert species.

No worm under the one I removed. The knife edge made the small puncture in the surface. The lesions will not easily flake off. The plant mix its in right now does have too much organics in it. I'm making trip to Los Angeles next week to get to pick up 10 bags of my favorite mix and 20 various sized bowls from a wholesale house I have an account with. and I will be spending days repotting a 100 or so plants that were put in this mix. It has been treated systemically with both an anti-fungal and a general systemic mix. When I was in England in October I repotted a friends cactus in new pots and the mix I got there was real sandy with no organics. IIt was a really nice commercial mix branded under a generic name.Its not available in the states however.
Thanks guys for the response. Lets see how it does over the next few months.

mikethecactusguy wrote: ↑Tue Dec 20, 2022 3:16 pmI'm making trip to Los Angeles next week to get to pick up 10 bags of my favorite mix...It has been treated systemically with both an anti-fungal and a general systemic mix.

Sounds promising -- if they sell their mix in 20-lb. bags, one bag would last me a good long time (nice thing about having a small apartment collection). If they do, please give me the name and address of your source. Even though I have only a handful of cacti that need soil in their mix, they're overdue for repotting, and that would be a fun little project for early spring.

Steve Johnson wrote: ↑Mon Dec 19, 2022 10:44 pm -- good sandy loam seems awfully hard to come by here in the US. Too bad, because that will minimize the possibility of fungal attacks for pretty much all desert species.

I have access to good sandy loam. I would have to test it to be a 100%% sure though. How would that fit into an all mineral substrate (6 parts pumice and 4 parts DG/gravel)? Why is it beneficial regarding this case?

ohugal wrote: ↑Wed Dec 21, 2022 7:27 amHow would that fit into an all mineral substrate (6 parts pumice and 4 parts DG/gravel)?

I don't think I've asked before: What does "DG" mean?

Decomposed granite. I use grit/stone gravel. I don’t have easy access to DG.

ohugal wrote: ↑Wed Dec 21, 2022 7:27 am

Steve Johnson wrote: ↑Mon Dec 19, 2022 10:44 pm -- good sandy loam seems awfully hard to come by here in the US. Too bad, because that will minimize the possibility of fungal attacks for pretty much all desert species.

I have access to good sandy loam. I would have to test it to be a 100%% sure though. How would that fit into an all mineral substrate (6 parts pumice and 4 parts DG/gravel)? Why is it beneficial regarding this case?

I have a Tephrocactus inermis and a Tephro papyracanthus I purchased as rooted segments about 11 years ago. I tried growing them in a soil-less mix, but their thin scraggly roots wouldn't support it. When I repotted them in a 50% soil/50% pumice mix in 2013, they started growing wonderfully. I also have two Eriosyce senilis that enjoy growing in the same mix. Pumice gravel lasts forever, but I wouldn't say the same thing about the soil component. Could be wrong, but if the soil is exhausted after 11 years, changing it out with fresh soil in the 50/50 soil and pumice mix is advisable IMO. The rest of my cacti have been doing remarkably well in the soil-less pumice and granite gravel mix. Since Mike lives in the dry heat of the desert, a soil-less mix would probably dry out too quickly in the spring and summer, so I'm sure that he needs soil in his mix for better water retention.

The worm is small you need a 4X to see it . More like a white grub or maggot than a worm. imidacloprid insecticide a systemic will take care of it but only if the plant is taking up water. I've thrown cactus away with bad scale infestations. If its fungus its the weirdest fungus I've ever seen ? Maybe some desert fungus ? I would repot the plant and dispose of the soil at any rate.