Perhaps, aphids.

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Steve

not Steve

Those trees are bug magnets. Might be black aphids.

Dan

Are Black Aphids any worse than regular green ones?

They are both horrible in my experience, though the green ones are more common in my yard. Most years they don't show up in large enough numbers to be a real problem, but when they have a population boom it can devastate whatever plant they're on. I use Safer soap and water and can usually get rid of them without killing off all the ladybugs.

I've got a sweet cherry tree that gets covered with those things, every year. I need to figure out a way to spray it early enough to knock them back, and then let the natural predators build up a population.

They also will infest willow trees. And then come the wasps, by the hundreds, to feed on them.