I don't really know buckthorn very well, and I never really thought it could get that big, but that is my first thought on this. Rhamnus is the genus.

You could try predatory and parasitic insects.

Here is a link that might be useful: predatory and parasitic insects

thank you esh............

if they are in fact aphids.. you can ignore them

plagues come and go over the years.. and RARELY actually kill a tree .. though it might not be pretty by fall ...

you may have black honeydew mold on things below it.. which will wear away diuring winter ...

and you will have ants .. 'milking' the aphids for the honeydew ...

but disgusting as it all sounds ... the tree most likely wont die ..

the normal course is to simply water blast the tree... reducing the population ... just with the hose ...

ken

I'm curious as to what this tree is as well.

I do believe esh nailed it......that it's a buckthorn. I couldn 't bring it up and knew I'd seen them before. Some can make it to 25 feet and they often have multiple trunks like the one in the picture. It is much more well behaved than the enormous maple over my chicken yard and I wish I'd been more careful about what trees I let grow nearby. Gives them needed shade in summer to keep the poultry cool and makes an enormous difference. But have had to have arborists in to limb it several times.

Hmm, bark didn't look right. Although I've never seen one that old/large. Do they have red fruit?

The link in the original post has a lot more pictures.

The pics of the flowers should be good for id, but I am not sure how they compare to google pics of buckthorn. Most flowers are quite different, but there might be male and female kind of flowers that don't look the same

First I would like to thank you all for taking the time to check this out and share your knowledge.
there are2 of these in our small yard. across from each other. the other is much smaller and also almost dead from(i believe) the scales. i know they are aphids now and yes lots of ants but i think i have had scales in the past. there are also lots of ladybug larvae. the smaller tree has the same flowers i think. i will check in the morning. it produces a red fruit the big one does not. last year was the big ones healthiest since we have been here and it held its leaves very late into the season.
so a buckthorn it is. thanks. another mystery solved by the fine folks on GArdenweb!

I was under the impression Buckthorn produced blue/black fruit not red. So I don't know if you have a 100% tree id yet.