I've never seen anything like this before, and out of many (12+) flats of various types of seedlings, only the three 6-packs of celery are affected. The same potting soil was used for everything. The little white specks don't seem to be moving, as far as I can tell (at least not yet). I'm wondering if this could be something that came with the seeds?

Aphids?

No - unless it's some stage i've never noticed before... it looks like tiny pieces of very fine thread all over the plants and the top of the soil.

With 2 of the 3 6-packs I uprooted the plants (they're still quite small, a couple of inches tall), shook off most of the potting mix, removed the leaves that were most affected and washed the plant off, then repotted in clean packs with new potting mix; with the other pack I just stirred the top of the soil up and removed the worst leaves. Put them in a clean flat and away from the other stuff and if it comes back I'll probably just discard the plants. Very curious as to what this is, though!

I'm seeing what looks like plump green aphids amongst a bunch of their white, shed exoskeletons.

Danita said: I'm seeing what looks like plump green aphids amongst a bunch of their white, shed exoskeletons.

That's what I thought too, you can see several of those green aphids!

Shed exoskeletons! Yes, I think you hit on it, Danita; and I think I see the aphids you are looking at in the photo as well, although I didn't see them on the plants... I must have been too focused on all the white stuff. Odd that they don't seem to have moved to anything else, though... I'll give all the flats a good going over again. Thank you!

Not unusual at all. There are about 5000 different species of aphids. The ones that love my plum trees couldn't care less about my brassicas. The cucumber loving aphids will totally ignore my artichokes even if the vines are running all around them. But when the artichoke loving aphids show up they really mean business1 Even my ladybugs can't keep up. The little jerks that love my beans hate my squash even if they're growing side by side.

Most of them are pale green but they can still be many different species. And each is a connoisseur of different plants. And I now get them in many colors. The super vivid yellow ones only eat my milkweed. The black ones prefer beans only.

Can you tell I've been having lots of problems with aphids the last 2 years. Year round! And they can easily live at 115* and freezing temperatures doesn't kill them either! And they couldn't care less for nasturtiums which are supposed to be an aphid magnet and I've got the flowers growing everywhere now to no avail. Well, at least they're pretty and edible.

That's quite interesting, Debbie, thanks for that info -- I've had very little trouble with aphids over the years, actually only remember a couple of times and one of those was when I had peppers growing in my high tunnel and was only bottom watering (once I started spraying the plants with water the aphids disappeared).

Following up on this - I've been carefully checking the plants a couple of times a day and this morning discovered some of the tiny white things crawling along the edges of the plastic 6-packs that the celery is in. (I still have not actually seen any aphids.) Thrips possibly? I'm going to give some insecticidal soap a try and .