How to Kill the Roots of a Crepe Myrtle Cut the crapemyrtle down to just the stump with a pruning saw and loppers. Paint the stump with a glyphosate systemic herbicide with a disposable brush soon after cutting it down. Cut down new shoots as they sprout with hand pruners and paint them with more herbicide. Things You Will Need. Tip. Warning. References (2) Click to see full answer. Simply so, will vinegar kill crepe myrtle?Using Epsom salt & vinegar to help with trunk. ( I can’t grind b/c of location.) The only way to kill a crepe myrtle is to have the stump removed.Also, can you cut back a crepe myrtle in the summer? Summer. June signals the start of crape myrtle’s blooming season, although it may begin a few weeks before or after the start of summer. The only pruning you should do at this time is to remove branches for the health of the shrub. Additionally, how far can you cut back a crepe myrtle? Remove low branches I like branching to begin 6 to 8 feet off the ground because it looks better and is more practical. If you don’t need to walk under the branches or see through them to view oncoming traffic, you can allow the branching to start lower. Prune unwanted low branches all the way back to the main trunk.How do you stop crepe myrtles from running?Prune suckers as soon as they appear with sharp loppers as close to the roots of the crepe myrtle as possible. Dig the blades of the lopper into the soil an inch or so before cutting. Do not leave a stub above the soil surface because it will leave the tree susceptible to disease and insect invasion.