Problem with apple tree suckers

Hello,
I have a problem with very persistent apple tree suckers growing in an area of my garden that is supposed to be having a play surface installed. In order to sort this out, we had the apple tree cut down and I have drilled holes in the stump and put root killer in. However, the suckers have all burst into leaf. I also have another apple tree close by, but was advised that it was unlikely to be the culprit due to the position of the suckers.
How long do roots and suckers take to die back? Could it have actually worked but is just taking time for the poison to reach the suckers? I can't go ahead with the installation of the play surface until I know whether or not the suckers are going to die off. At this moment in time they look pretty healthy!! I had the tree cut down in October last year, and poisoned the root about February. Any advice gratefully received. Thanks.

 

I have a feeling you need to kill the suckers, I dont think just killing the stump will stop them.

It depends on what you are using I guess, but I'd let the suckers grow away and treat them with glyphosate in a couple of months or so time.