Often the easiest aphid control is just hosing down the plant periodically with a strong stream of water. With a large tree this is a bit tricky to accomplish :-) But it IS the easiest and safest method. Otherwise you could consider releasing predatory insects (ladybugs, lacewings) to help. Other predators - birds, parasitic wasps - are typically present in quantities sufficient to help keep things in control, provided you don't use spray pesticides.

The systemic insecticides DO help but it's too late in the season for them to have much effectiveness now - these need to be applied early enough so the chemicals can be absorbed by the tree before the aphids invade. And that sticky stuff is referred to as 'honeydew' and is the excrement of a variety of sucking insects like aphids but also scale, whiteflies, mealy bugs, etc. Some trees - birch, linden (Tilia), and various fruit trees - can be very attractive to aphids. And while they generally do no long lasting harm, the generation of the honeydew is a nuisance, as is the sooty mold it encourages.

ID the tree ... [pic of leaf and bark will get you such]

then get rid of it if it is an aphid magnet ....

there are some trees.. that simply arent worth the money invested in 'fixing' them ...

plagues come and go ... and i have had such.. once in a while .. on a tree here and there around the garden ... but NEVER has it been a repeated problem on the same tree... year after year ... that is the part that is making me wonder why this particular tree...

scale can do the same ....

ken

well, that may be a bit of an extreme suggestion :-) Mature trees are a bit hard to come by and removing one simply because it can get aphids is often overkill. Aphids are probably one of the easiest insect pests to control as well as generally producing no long-lasting damage.

What is a "classically shaped " leaf? Truly, having an identification of your tree could lead to many insights. Pictures, please.

never use chemicals.. until you have ID'd the host.. and the culprit ...

if the dude cant ID the tree... why should we presume his definition of the bug ..???

when we guess.. we make a 'gu' out of 'e' and 'ss' ?????? .. dont you think.. lol ...

if the chem is NOT labeled for the given plant.. then it is an illegal use...

same if the chem is used on an unlabeled bug... dont you think gal ...

but as gal notes.. if all you want to do .. is shoot water all over the place... go for it... worse that can happen.. is the neighbors start worrying about you ...

but again.. why this particular tree.. year after year.. after year?????

ken

Birches in our climate harbor aphids year after year with the sooty mold underneath them. If you really want one here you can't have it near where you park or near the house. That leaves left field in the back yard, and you still have that sticky goo on everything.
I have ten acres and refuse to grow a birch on it or any plant that I have to spray or gives me trouble. Too many other nice ones to grow instead.
I'm with Ken, cut it down and be done with it. It's a mistrake. ;-) Move on.
Mike