I have your article with great interest. Unfortunately I have a 35' Linden tree that is infested and my neighbors have six infested trees as well. We don't have the equipment to spray the trees, nor are we interested in spraying, due to a decorative pond in the area and pets.
We are seeking a solution which can be administered through the soil. Two tree care people have been out and want to charge a fortune per tree to treat. Can you tell me what chemicals I can use. One of the estimators said that the chemical they use (which he wouldn't name) was a professional use only product when it was new about 10 years ago, now is "over the counter." Any idea what it is, or what I could use? Do you sell it?
Aphids can be treated with a product called MERIT WP. This product can be sprayed but it can also be used as a systemic. When used as a systemic, it is mixed with water and applied to the soil. The process takes awhile to work but once applied to the surface, it will be absorbed by the tree roots and work it's way to the foliage. There it will kill off aphids as they feed on the leaves which are now effectively "treated".
The MERIT WP LABEL has a section how to apply it as a systemic and it appear as though you could use as much as 2 oz per 30 inch diameter tree. That means it could take a significant amount of your Linden Tree. But you didn't mention the trunk diameter so I can't say for sure how much you should use. I do know you can get a discount on every two jars of Merit you buy so since your neighbor needs to treat too, maybe you can go in together on a purchase to save on cost.
Lastly, I highly recommend you treat some of the surrounding trees with one of the products we have featured in our APHID CONTROL article. This will insure they don't become infested too which is highly likely over time if nothing is done.