Aspen trees are not single trees but one large connected organism that propagates by sending up suckers. Suckers can be pruned out of the lawn.  Products such as Sucker Stopper could translocate to the mother trees. Also, if you read the label of these products, I believe they are not recommended for use on any trees in the Populus genus, which includes aspen, cottonwood and willow.

Instead, continue on a mission to cut back and mechanically remove the sucker as they emerge. Unfortunately, aspen propagate via root suckers, and their natural methods can be a headache for gardeners.

Best of luck,

Paula 

Weld County Master Gardener