Please help! TINY black specks on underside of leaves on my Chinese elms and Hawthorn. This has been a reoccurring pest for at least 4 years now. It's on the underside of all the leaves on each affected tree, and I mean ALL the leaves - the ENTIRE tree. The spots don't seem to damage the leaves or tree; growth has always been healthy so I haven't worried too much, but a couple of my trees should be ready to show in a year or two and I'll definitely have to rid myself of this before then.
The specks don't scrape off easily by fingernail, at least without damaging the leave. I've tried neem oil to suffocate them, and I experimented with brushing diatomaceous earth on them with a q-tip, but neither had any effect. When I do scrape one off, it's thinner than paper and doesn't seem to be an insect body... but it's too small to say for sure. I searched online for different species of scale and that doesn't seem to match. I need ID to research life cycle and find out how to get rid of them!
i wonder if this could be fertilizer or light or something else entirely unrelated to a pest. i've looked at this picture three times and really can't figure it out. i would snip a leaf off and put it in the fridge (to keep it fresh) and see what happens.
Thanks for the suggestions guys. I'm pretty sure it is a pest, because it is ONLY on the underside of leaves, never on the top. If it were residue of something else, it would most certainly be on the tops of leaves as well... The dots are very small so it is impossible to tell whether they are bodies with the naked eye, but I just spoke to a friend who has a microscope and we're going to take a look at them this weekend... I'll let you know how it looks.
I'll try submitted the question to the garden pest and disease forum also.
STILL HAVE NOT IDENTIFIED. I looked at it under a microscope and it's so dark it is hard to see structure, but it is definitely a bug, not a fungus/virus. I can make out appendages, barely. Still no clue as to ID. Summer's in full swing and the things hold up fine to the heat, haven't seemed to change in size, numbers, placement. They scratch off the leaf by fingernail a little easier maybe...