We have a couple of sycamore trees that are apparently infested with aphids. Our cars are covered with honeydew at this time of year. From what I’ve read ants don’t tend this type of aphid so any attempt at controlling them would be pointless Ladybugs are a natural predator and can be purchased online but how many do you need to treat a large tree? Do you just open the bag and hope for the best?
Talk to your local nursery. I’m sure the answer will depend on tree size, the weather and exactly what kind of aphids you are infested with.
Good luck! I love ladybugs.
Ladybugs aren’t a panacea. I tried them twice for aphids and the ones that didn’t die flew away. Check to make sure your climate and plant types are right for ladybugs, and don’t trust the nursery–they’re trying to sell you the things.
Try your local cooperative extension for better advice.
My experience has been that they work, but not many stick around. They offer short term help, but not a long term solution, which makes sense. After they chow down, they head off to look for more food.
I just fought an epic battle with aphids on my cherry trees. But they are small trees and much easier to treat than a giant sycamore.
(I used DE !)
Still, I feel your pain and wish you good luck in your battle!
Honeydew? That’d sure make a real mess of the duco. Those suckers can weigh up to 4kgs. 
Judging by the amount of honeydew on my car, I suspect they could spend a long time on our trees. I was hoping for a long term solution. Ill try the coop extension service. That’s a good idea.
Aside: When I lived in Montana, I had an aphid problem in my garden. I knew that some of the garden catalogs my mom got sold ladybugs, so I figured I’d be able to find some online. I go searching, and discover that the nation’s largest supplier of beneficial insects was just across town.
In my case, they worked, but the aphid problem wasn’t all that bad to begin with.
How long have you had this problem?
Ooh. Fun. I would buy lady bugs just for fun. A big sycamore tree is gonna be hard to treat. Call a tree service and ask.
I’ve founds it helps to wet the area where you want them to hang around, and release them in late afternoon. You may need to release another wave of them in a few weeks.
The problem with ladybugs is that they fly away home.
There are systems which involve injecting pesticide into the tree. I’ve found that injecting Imidacloprid controls aphids on Cottonwood trees for several years. Imidacloprid is a neonicotinoid, which may be bad for bees, but it will stay in the tree(s) where it belongs. http://arborjet.com/arborjet-advantage/
Be sure they know you have insurance and a volunteer fire department.
I think the ladybug (or other predatory insect available for purchase) idea would work best in an enclosed setting like a greenhouse. As noted previously, most of the ladybugs released outdoors would zoom off to other locations, and the presence of a severe aphid infestation means you’d need a ton of ladybugs to have a initial significant impact.
If the trees are considered valuable, getting an expert treesperson to advise on the least toxic and effective treatment would be a good investment.
But only if some cruel child deceives them into believing that all of their children burnt to death (except possibly one).
That’s why they should know about insurance and fire departments.
DE is great for pest control in a home but how do you get it where it needs to be in the tree?
As I said, both are small trees. I did it on a ladder, with a squeeze bottle with DE in it. Every squeeze would send out a fine dusting. It wasn’t difficult to coat all the leaves, just time consuming.
Orchard owners use powerful water hoses to blast them off too, apparently. I tried that but it was the DE that really worked.
DE being, I presume, diatomaceous earth.