What (and when) is the best way to treat what I think is a heavy aphid infestation of our Aspen trees? We've tried spraying it with our hose on high and used some insecticidal soap, but there are still A LOT of bugs on all 5 Aspen in our yard (2 are more heavily impacted, than the others) and we are wondering if we need a chemical. I can see the insects all the way up, higher than we can reach with our treatments, and we also have the honeydew excretion and a bit of mold as well. We are willing to call a pest company, if needed. 2 smaller Aspen trees didn't get leaves this year and seem to be dead and we are worried our beloved backyard grove will be impacted. Thank you!