how are you applying roundup????

if you are spraying... you are losing ...

it is labeled.. or used to be.. as a stump killer at 100% of the concentrate...

use something like the very expensive applicator at the link ... mark properly... return unused to its proper container ...

cut trunk ... apply to the green edge of the cut stump ... one drop on things less that pencil size ...

ken

Here is a link that might be useful: link

You can definitely win the fight, if that's what you want to do. As Ken suggested, use undiluted glyphosate/RoundUp (it's not 100% concentrate, BTW, but usually somewhere between 18 to 41%). The premixed stuff, made to kill easy-to-kill grass, is not gonna do much. And, the regular formulations, as opposed to the quick-results formulations, work a little better for this application.

Other things to keep in mind are that you need to treat all the suckers that are present at one time (same day), and, you need to treat the freshly cut phloem of the stumps within a short time of when you chop off each sucker. Cutting them down and then coming back to treat hours or days later is probably not going to work. Finally, you will probably have to do this a few times (4 or 5 maybe) for the root system to be completely killed. Properly treating the tree stump when the tree was cut would have made all this soooooo much easier, but it's still do-able.