This is mealy bug, highly contagious among plants, swab off w/ q tips dipped in alcohol every 2-3 days &/or discard plant(s). Must isolate them from other plants.

Agree that it's mealybug, and killing the adults with a Q-tip dipped in alcohol can keep adult populations in check. There's a problem with that method, though. The adults need to be mechanically removed with the Q-tip, and that method has no impact on the pests present that are in the crawler or instar larval stage. Eggs hatch about every 10 days at about 75*, with the interval increasing inversely with temperature.

You could try horticultural oil labeled 'Summer', 'Perfect', or 'All-Season' mixed with insecticidal soap, both at recommended rates, neem oil and alcohol at 2 week intervals (ask for recipe if you want it), or spray with Bayer 3-in-1 insect/mite/fungal control. This systemic product is listed as safe for use on houseplants, but the spraying needs to be done outdoors.

I'm really sorry you lost so many plants to this pest, especially since it's not that difficult to control once you figure out what it responds to. Good luck!

Al

I've used a fungicide earlier, so I guess I know why that didn't work.

I realized something; one of the plants that wasn't affected (a quite large and somewhat sickly apple tree, grown from a discarded piece of apple) had an fly issue during the same period, and I used a environmentally responsible insecticide on it. I still have a bit, and will see if the other plants respond the same way.

Thank you!