Going Nuclear on Scale

[Worm]

My poor Ferocactus macrodiscus has been dealing with scale (same type as this internet picture) for ages now. I've tried spinosad spray and scraping with a toothbrush which works well to remove scale but doesn't keep them at bay for long. I can find a variety of other insecticides people recommend online but I'm curious to see what you all have used and whether it worked, thanks.

[Samhain]

I’ve done hot water bath for small enough plants.

[Worm]

Thanks, but how hot is too hot? I don't want to burn the roots off either.

[Stan]

Since you tried all...Bayer systemics is left. Altman uses it.

[Gee.S]

Blast it off with water, then spray with Malathion (or some such), perhaps once every 2-3 weeks until gone. An even more important point is to reduce the plant's stress, which is probably why the infestation occurred in the first place. Happy, healthy cacti do not generally suffer scale infestations. So work out why it was unhappy and remedy as needed. Ideally, you want to get the plant healthy enough to help fight it off. And keep it off.

[Worm]

I couldn't find any of the pesticides mentioned here, I might try again later or keep on with neem & spinosad according to Gee's method. About possible stress, the plant seems healthy in every way, good color, spine growth, and it's putting on size well. My best guess is that it's just an issue of the plant's young age and small size. With time and pampering perhaps it will resolve on its own