Lindens, little leaf in particular, have their own species of aphids that will infest the trees seasonally. Extensively planted as street trees in London, they are in the process of being systematically removed simply because of this problem - sticky honeydew being dropped onto parked cars and passersby.

To the best of my knowledge, ants farming aphids are a restricted to only certain species of aphids, therefore I'm not sure you will accomplish much by restricting the ants, especially since they have not yet been apparent on the tree so far.

Spraying the tree with a strong stream of water is probably your best bet for control with minimal side effects :-) It serves to dislodge and even destroy the aphids as well as washing off the sooty mold. And easy to do with the frequency required. Insecticidal soaps can work also, but you have to actually coat the insects to effect proper control and you've already determined the difficulty of that with a 35' tree! And insecticidal soaps can create a phytotoxic situation if the timing is not considered properly.

Systemics can certainly help. Bayer produces a tree insect systemic that is quite effective against sucking insects like aphids. It is an imidacloprid-based product and is quite toxic to bees but if used as a systemic, relatively harmless to anything other than sucking or boring insects. Not sure that I'd consider systemically treated fallen leaves as 'poison bombs' - just as harmless and compostable as any other untreated leaf.

Remember that this will be an ongoing battle :-) If you want to keep the linden, you will have to deal with the same problem every spring.

Thanks for the great info.

I'd like to try the isecticidal soap at least once and then do the strong stream of water from that point on.

Regarding the phytotoxic effects, can I avoid that by spraying at sundown on a day when it's under 85 degrees? I don't want to hurt tree.

How long does it take the bayer product to work from roots to leaves?
Is it really safe once the leaves fall off? Once the sooty mold takes root, its like autumn all summer long. The leaves are everywhere. I am mulching them with my mower and the dust they generate is pretty heavy. If there's enough poison to kill the insects in those leaves, I'm worried about inhailing it.

Also, any thoughts on the Safer brand 3 in 1 product that contains sulfur? The MSDS says its not a hazard to humans, but I don't know about it hurting the tree.

Yes, the chances of a phytotoxic reaction are greatly reduced if the product is applied late in the day and/or out of direct sunlight.

Can you rake up the leaves and dispose or compost them? You are probably at greater risk from inhaling the mold spores than you are from the imidacloprid. The insecticide's mode of action affects neural pathways of certain insects and these are not present in humans or other mammals, so the chance of toxic doses are pretty low, if they exist at all. And there is also a very good chance all that dust you stir up when mulching the leaves with the mower is just dried leaf particles :-) But I'd still be careful with regards to the sooty mold.....like any mold, not healthy to inhale.

I'm not sure how long it takes for the tree to absorb the Bayer product and translocate it to the leaves - as long as it takes for a tree to absorb water from the soil, I guess ;-) Apparently the product is bound and not easily absorbed by the tree if the soil is highly organic, so remove any mulch before applying.

I can't speak to the Safer product except that it is considered safe/natural/organic, what have you. I just have reservations about applying something (the sulfur)without reason.....you don't have a fungal problem so why apply a fungicide? I'd prefer to use a product that is designed for and targets the immediate problem. The broader the spectrum, the greater the environmental impact.

Thanks so much! Great info. I feel safe about the imidacloprid after your explanation and reading about its its toxicology on several sites. I'm going to try to find out how quickly it works to see if I should still do the insecticidal soap.

Is there a specific Bayer product that I should use? I am checking out products on their site, but if there is an obvious answer please let me know.

Also, would imidacloprid be effective on Mimosa Web Worms? They attack my Honey Locust each year and I was going to try Bacillus thuringiensis (I think) since it seemed non-toxic to humans. Any other easy insecticides I can use on them that are pretty safe? This is another tree that showers my deck and house with debris, so I want something safe.

BTW, I was thinking of using the product with sulfur hoping to prevent the mold growth. From past experience, the mold seems to start pretty quickly after the aphids appear.

The Bayer product is Bayer Advanced Tree and Shrub Systemic Insecticide. And yes, it will be effective against the webworms also.

If you control the aphids with the insecticidal soap, imidacloprid or even the water spray, you won't have to worry about the sooty mold. It only forms/feeds on the honeydew - the sticky excrement - of the aphids. Get rid of the aphids, no more sooty mold and no need for the sulfur!

That makes sense...for next year. The leaves are already coated with honeydew. I'm researching sulfur now.