[CANUFNET] aphid infestation in Basswood

[Bartram Woodlands]

Um, I have a client with a 70' Little leaf Linden in Backyard, covered  
in soot from heavy aphid infestation throughout this year and dates  
back to late summer last year.

Tree is dripping honeydew on nieghbouring property and all plants/ 
shrubs in garden now sooty. How do you spray a 70' tree repeatedly to  
remove aphids?  Do oil sprays work in spring? Aphids are now gone,  
likely in bark I presume. Would imidacloprid be effective. Guelph has  
banned cosmetic pesticide use.
Tree although healthy seeming is boxed in by other trees and heavily  
limbed. Plan to prune lower/ small limb to increase light through  
lower canopy.

Any assitance appreciated - Thanks ,

Dave Bartram