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):

A relatively healthy leaf


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?

  • Would you say fly's are pretty common around your house? – Rob May 14 '19 at 15:08
  • Not at all. The Bonsai sits on a windowsill facing a yard with a number of trees however, so it gets some limited exposure to what inhabits those. – Johannes R. May 14 '19 at 17:03

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