Does anyone know what this is?

[Newbluecactus1]

Hi

I bought this blue Myrtle cactus a month and a half ago and I remember that there was one of these small white spots when I first got it, and over the weekend I've realized that these spots have appeared everywhere.

Does anyone know what these are? Any help or tips on how to get rid of them would be great! Thanks!

[greenknight]

Looks like scale insects. You can scrape them off for starters - http://www.cactiguide.com/cactipests/#scale

[hegar]

Greenknight gave you a good guess. The whitish round, slightly raised structures may well be the covers of female Diaspis echinocacti armored scale insects. This insects body is hidden underneath the shield-like cover. If you do have a hand lens, remove a large cover using a probe (pin), inserting it gently under the cover and pushing it off. If you are careful enough, you will see the insects body either exposed on the cactus or perhaps coming off with the cover. The female armored scale has a flattened body and is legless. It attaches itself to its host by a feeding tube and remains there until its death. Going to the index page (home page) here in CactiGuide, you can click on the button "Diseases and Pests" at the top of the page and scrolling down you will find the scale.
Combatting these insects is not easy, because they are very prolific and lay many eggs. The freshly hatched offspring (crawlers) are mobile and will attack any cactus they like to feed on. I have found these pests on prickly pear, Pachycereus marginatus and also on the cactus Myrtillocactus geometrizans (your plant).
In my opinion, the best way to fight these tough critters is through the application of a systemic insecticide. I do use Bayer "Tree and Shrub" insecticide, which does have 1.47% imidacloprid, the active ingredient. On the bottle it says, that you only need to apply this poison once per year. The roots of the plant pick it up and translocate it throughout the plant, making every cell toxic to would be insect feeders. There are other systemic insecticides available to the general public. Imidacloprid has been implicated in causing bee death, but I am not sure, if it was the cause of the "colony collapse" problem experienced by honey bees.
You could also try to get the number of these insects reduced by using a toothbrush dipped in rubbing alcohol. That would kill a good number of these scakes, but you would need to treat your plant again and again. You may never totally extinguish the scale population though.
Good luck with getting rid of these little beasties. They certainly are a tough foe. It would be nice, if your problem were something else. However, if the whitish circular spots are increasing in size and number, it is high time to get going with the treatment.

Harald

[greenknight]

The link I provided leads directly to that article in "Pests and Diseases". Good info from hegar, though. Soap sprays are also effective against the crawlers, I hear, but won't get the adults under those shells.

I don't have his experience with them, only once - one appeared on a Cereus peruvianus, and I scraped it off. End of story. When they've had a chance to reproduce, though, you've got a much bigger problem.

[Newbluecactus1]

Thanks guys for the help! Will put all your good suggestions to work!