My Chinese elm suffers from an infestation that I am having a hard time diagnosing & treating. About a week ago, I noticed tiny, rod-shaped white spots, mostly on young leaves, which spread rapidly. Some close up images (complete set including videos here):
Other possibly relevant information:
- Afflicted leaves suffer quite a bit, particularly the young ones.
- I've not noticed any other stadium of those insects, in particular no winged forms. That seems to exclude Whiteflies & Thrips. My googling skills have not turned up any other common pests that match those in appearance.
- I've submerged the tree in soap water for ≈ 30 minutes on two consecutive days: That seems to curb their population a bit, but it unfortunately quickly rebounds (within ≈12h).
- I am based in central Europe.
So, my question is: What could this be and how can I treat it?