I had a similar problem last spring. Really struggled with scale. Moving the infected plants outdoors turned out to be the best way to get rid of it. Natural predators did the trick.

Down here in the metro, it's getting warm enough to harden off some seedlings--e.g., spinach--but it's still too cold for basil and tomatoes. So the "moving outdoors" solution depends on the type of seedlings you've got.

I've used neem oil, but not for scale. It can be pretty harsh so I wouldn't assume it's okay for seedlings. Why not try a diluted version of it on one and see what happens?

That's a great question! I have some variety of spidermite which seems to migrate from mature plants to certain seedlings. Last year this was hard on impatiens. This year it's on datura, moonflower and maybe peppers. These mites are under control on mature plants but the seedlings are different. I wondered about neem too, has anyone used anything mild that works?

Well, I spayed some Neem oil diluted in water on the tomatoes and sumflowers and it seemed to stress them a little. They're still ok for the most part but some leaves are a little off color and curled. Maybe it's more than seedlings can handle. When I sprayed more mature plants with this solution it was great at taking care of some blight.

When the scale was really bad, really scaley I went after both little trees with a cup of neem solution and a tooth brush. It was really amazing how much of of that junk just brushed off. Following that I gave them all a shower, and a spray of neem solution. Seems to work well to get them cleaned up and looking good.

Scott