Just noticed the yellow dots on my Mammillaria. They're stuck onto the surface very small. The is some webbing but that could just be from the base of the spines. Any thoughts if it is? Want to make sure it doesn't spread if it is!

These are the best photos I could take..

It looks like scale to me, or maybe just some debris or soil that got trapped in there under the spines. I don't have any experience with spider mites (they hate our humidity, thankfully). Maybe you can try to rinse off the body of the plant next time you water, and that may help you figure out if that stuff is living or dead. The treatment for scale is basically removal, using a Q tip soaked in alcohol or a toothpick, followed by a spray of 70% alcohol or insecticidal soap (or 1-2% mild dish soap in moderation). Sometimes it's hard to get in there under the spines.

Mature scale insects that stick to succulents do not have legs, so once they are removed from the picture they are very unlikely to come back. Some juveniles that you may not necessarily see may take hold, which I why I recommend the spray and a followup every week or so until you're sure they're gone.

Thank you Baja. Just being reading about scale and the photos look very similar. I also found thrip which looks similar with the white fur. Should I be worried that my other plants have been close by for around a year and should I treat them too? No signs on them but my new one has these marks, armoured scale?

This is the scale I think?! 🤔

It's the right size and color, and if it was stuck on the plant pretty hard then yes, that is scale.

Baja_Costero said:It's the right size and color, and if it was stuck on the plant pretty hard then yes, that is scale.

That's brilliant thanks for your help. I've removed most of them by hand and now going to order some insecticide soap to ensure they've all gone. Should I treat the rest of my collection as a precaution?

I suppose you could. I probably wouldn't. If there's another plant that was adjacent, maybe. Scale is a funny thing, given it's generally hard to detect until it's a full on infestation. I deal with it pretty regularly here. Who knows where it comes from, or where it could be simmering below the level of detection, but some plants are much more susceptible than others. Time and experience will teach you this. Now that you know what to look for, you should keep an eye out, just do a quick inspection when you water or whatever, so that you can nip this in the bud if it comes back.

In theory we would be putting new plants in quarantine, to observe whether or not they may be bringing diseases into our collection, but in reality most people just put them right on the shelf, or the windowsill, or whatever. I would assume that pests will be an infrequent, occasional problem in the future, and not assume that you can keep your area completely bug-free indefinitely. The earlier you catch them, the better for the affected plant and every other plant around it. Vigilance is key.

There is a preventative treatment for scale if you find it a recurring problem with certain plants, and that would be a systemic insecticide that the plant takes up to acquire resistance, but it's probably a better idea just to observe for a while so you know who is susceptible and who is not.

Thanks again for all your help and advice. I've kept the infected plant separate for now and ordered some insecticide soap so will get it treated and observe the others too.

I don't think it was scale.

I see some dried up flowers on the Mamm. I know what brown spots you're referring to, but I'm not sure what they are exactly (but it's not scale). Almost like small scabs on the cactus. They can be a little raised, it's not scale. Some of my cacti have the same things on them.

Same with your other cactus. The big one looks like the cactus was punctured at some point and healed around it.