Black willow aphid infestation
How do you treat this?. We have a huge weeping willow in our yard. These insects are all over the tree, our fence, deck , etc.
Washtenaw County Michigan insect issues
There is no cost-effective or very effective way to treat those aphids on a large tree. Sprays would require very large equipment and it still might not get to all of the branches where they are feeding. Trunk injections of an insecticide won't work well this time of year, and it would require a well-trained tree care person to do it. They don't come cheap, either.
I wish I had a better answer for you. A change in the weather, such a short cold spell, would probably slow down their reproductive rate and make more of a difference than trying to treat the tree.