I use the same treatment to quickly eliminate mealy bug and aphid
infestations. I returned the plants to the greenhouse, confident of my
success.
A week later they had returned, smirking at me in their arthropodal way.
Then I recalled the wise words of Michael Chamberland, and tried submerging
a few pots of infested plants. About 4 days underwater, then I brought the
plants back into the air.
No thrips.
My plants are going swimming this week. Fortunately the largest plants with
the problem are in 15cm pots. It would be a chore submerging mature plants.
B