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I have an Oak (Quercus) in a container grown from seeds, must be 6-7 years old now. And every year it gets these yellow spots on the leaves. When I look under the leaves, I see tiny little red/brown dots, which are the suckers, but they are as small as grains of sand. I can't distinguish legs or body parts or anything. They are also too small for a photo, sorry I only have a camera in my phone.

Does anyone recognize these yellow spots, and know which animal are causing them? Are this Spidermites? I didn't see web yet. How can I treat them (preferably in an organic way), I have tried spraying diatomaceous earth but that did not work.

Maybe interesting, next to this plant is a horse-chestnut (Aesculus hippocastanum), which has no signs from this pest (but will get a leaf miner problem later this year, I expect).

The plants are on a balcony (facing east) in Amsterdam, the Netherlands.

enter image description here

  • Could easily be insect caused galls. The bug larva will be inside the bumps on the bottom. – Wayfaring Stranger May 22 '18 at 15:26
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Those bugs are possibly Phylloxera glabra.

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    Please explain why you think so. For bonus points, explain how to control them. – Niall C. Jul 17 at 2:30
  • Thank you Sulev, a google search shows very similar leaf spots indeed. Do you have any advice in preventing or treating this? – benn Jul 17 at 7:24
  • It is impossible to give 100% proof based on this photo only. I just met very similar damage recently, hence suggested possibility, that here may be the same pest involved. The topic was initiated more than year ago, so I didn't suggest any measures against the pest. I don't have any first hand experiences, how to control that pest, but if the identification could be verified by the initial poster (because now it is possible to find detail description of the pest damage, and check, if those symptoms correspond to the current case), then it's easy to find recommendations from the Internet. – Sulev Svilponis Jul 24 at 20:22

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