Q.How To Get Rid Of Tree Suckers
I have suckers coming up all over my back yard and even one coming up from under my Deck. They are coming from the underground roots of the tree in the yard of the house behind me. I pull them out when they are small but they come right back, only stronger, Help, they will soon take over my back yard. Marley

Certified GKH Gardening Expert
Mowing will eventually kill the ones in the lawn. Others need to be clipped or dug out. The one coming up through your deck can be killed with glyphosate. Always read and follow label instructions when using pesticides.
https://www.gardeningknowhow.com/ornamental/trees/tgen/weed-trees.htm