Photinia threatening a comeback!

I live in a strata in New Westminster which was landscaped 25 years ago with lots of Photinia. Three of these were in the centre tier of a 3 level tiered wooden retaining wall and over the past three years two of the three got sick and lost all of the leaves by summer. I saw photos of Photinia leaf spot on the internet which matched exactly the look of ours. We thought they were dead so 3 weeks ago we cut 2 of these 15' high trees down to 6" stumps as we did not want to treat the trees with the expensive and perhaps toxic fungal treatment chemicals. Our goal was to replant with some smaller ornamental native shrubs and not gamble with large tree roots right next to our building foundation. Well these stumps have come back to life in a big way and are covered with new leaf growth. Digging out the roots would be very difficult because of the narrowness of the tiers.
Does anyone have any suggestions?

 

If you want to be rid of them, just rub off all the new shoots while they are still young and soft. That'll stop them doing any photosynthesis, and they'll be dead in a few months.

 

Or the leaf pathogen will do it for you.