A seventh ash tree was felled late last month, after concerns it could fall over.
Another 18 trees are under surveillance. Nine will be heavily pruned and nine will receive annual health checks.
The Wanaka Community Board approved the programme last week.
The trees to be pruned would have more than 10% cut out to rectify structural weaknesses and "major dead wood", parks manager Gordon Bailey said.
Asplundh arborist Robert Slater reported 19 trees were in "poor to moderate health with low vigour" and some were a health and safety issue.
The avenue was assessed as part of a district-wide tree review sparked by the death of Queenstown man Russell Liggett in 2009.
He was killed when a diseased poplar tree aged between 80-100 years was blown on to his car on Shotover Rd.
The avenue trees were brought from England during the late 1800s and planted at the Wanaka Station homestead site.
The district plan lists the "avenue of plane trees" as a protected feature but there was some debate last year whether it also covered individual ash trees.
Mr Bailey was subsequently advised resource consent was not needed to remove the ash trees.
Cr Jude Battson said she was worried the public would be upset when the trees came down.
Mr Bailey said a media release would go out in the next couple of weeks and Asplundh would do a mail drop to immediately affected properties.
Replanting would be normally be appropriate and the council was keen to plant more trees where space and conditions allowed.
However, the avenue was so closely planted and cast such a significant rain shadow it was doubtful whether new trees would grow.
