We brought a new little pine tree home from the nursery. I've just finished getting out all of the dead needles that had been gathering up (i.e. next to the trunk) so there's more room to breathe now. I noticed a cottony white substance on a few cones and tiny branches. I assume I should remove them. Does anyone know what this is? I didn't see any insects within the stuff. (I live in the Pacific Northwest.)

Thanks!

I would suspect aphids, mites, or possibly scale.
Keep the plant isolated or it could spread.
Try using an insecticidal soap or oil for control, and always follow the directions.

You would be doing the nursery a favor, to take the plant back and inform them of the problem, and possibly have the plant exchanged if you don't see any other infestations or your money refunded...

Spider mites. They're nearly microscopic, but what you're seeing is probably their webbing. Your best bet is to take the plant back. They're pretty hard to get rid of and spread easily. I've never had a plant survive an attack.

It turned out to be spider mites. Unfortunately, I forgot about it because my focus was switched to another problem (tree was yellowing, needed iron supplement). When I read jrepen's answer, I went outside to check the tree again. It was in serious trouble! Now the white stuff was on a very large section of the tree, and there was a branch in the middle of the affected area that had almost died out.

I tried this test, which is very important: (1) put a piece of white paper under the affected area; (2) shake the branch lightly until you see "debris and dirt" fall onto the paper; (3) start smearing the smaller pieces with your finger. A red trace means there are spider mites on the paper.

This test turned out to be very meaningful. When I returned the tree to the nursery (who very graciously accepted a return/exchange), I told them I thought it was spider mites. When they seemed skeptical, I said, "I did the smear test and there were red streaks on the paper." They accepted that answer right away.

I wish I'd paid attention to it sooner. I'm sure the tree will soon completely die. What a waste of a beautiful little tree!

Don't ignore anything, even if it seems minor! I could have caught this sooner and probably saved the tree. :(