Flat mites are becoming super common in the Hoya world, but because they’re so hard to see and do damage so slowly most people don’t know about them. A lot of cases of plants failing to thrive, never growing, or just looking sickly and slowly dying may be due to flat mites. You can see them easily with a cheap handheld magnifier, usually on the underside of leaves near the base.
Check out this link for more info: https://vermonthoyas.com/2022/11/09/lets-talk-about-the-new-hoya-scourge-the-flat-mite/
To cut to the chase, mix 2 tbs of sulfur with a gallon of water, shake vigorously, and put it in your sprayer. Shake frequently while spraying. Do it outside, we call it farting on our plants for a reason…
The gracilis (memoria?) pictured looked OK but it was next to patient zero, a fitchii that is just now coming back from the brink of death. The gracilis is suddenly growing like mad a month after farting. I left the sulfur residue on the leaves as a preventative so you can easily tell the new growth from old.
Interesting. I wish they sold this in Sweden. Best I can get is a product containing sulphur, but it’s not very cheap.
You might try diatomaceous earth. This is what I use for pests on my houseplants, and it works pretty well against anything with an exoskeleton. Cheap and available here in Germany.
You should be able to get elemental sulfur. Even if it’s not labeled a horticultural product, so long as it’s 100% sulfur you’re good to go.