Lilacs are beautiful ornamental bushes and, when healthy, add an air of whimsy and sophistication to a garden. However, a lilac bush can become a problem for any number of reasons. It may repeatedly fall prey to insect infestation, get in the way of other plants, or attract too many bees. Whatever your reason for wanting to kill your lilac bushes, know that simply cutting a lilac bush down will only make it grow back stronger.
Spray the lilac bushes liberally with a shrub and brush killer herbicide like Brush Buster. This is the least labor-intensive method of killing lilac bushes. However, as the lilac bushes die you'll be left with unsightly foliage.
Cut the lilac bushes down to the ground using an ax or saw. Whether or not you decide to spray your lilac bushes with herbicide, this is an important step in getting all of that foliage out of the way.
Kill the roots. There are several ways to do this. One is to liberally spray the stump with the herbicide. It will move throughout the lilac's root system and kill the roots. The second is to dig up the roots. Water the ground around the lilac bush liberally to loosen up the soil. Then use a shovel to dig around the circumference of the root ball and pry the root ball out. Once the lilac bush is removed, fill the resulting hole with topsoil.
Discard the plant. If the lilac bush was healthy when you removed it, and you did not spray it with herbicide, chop it into small pieces and use the plant as compost or mulch. If the plant is infected or covered in herbicide, throw it away.