How to kill ash trees
Ash trees need proper care, such as pruning every four years, to maintain their structure and form. Failure to properly care for an ash tree can contribute to the tree not growing correctly or healthy. Ash trees attract many insects, such as ash sawfly and ash borer.
Not only can these insects damage the ash tree, they can overload your garden with insects that may disturb your flower and vegetable gardens as well as your pets. If your ash tree has already succumbed to insects, it may be best to kill the tree yourself instead of waiting for more insects to invade the tree and your garden. There are different ways to kill an ash tree, depending upon size of the tree and the available manpower.
Cut a 5 cm (2 inch) groove into the bark of a diseased ash tree around the circumference with a chainsaw. This method, called girdling, will cease the flow of sap in the tree. This will cause the root system to weaken and the tree to die.
Inject herbicide into the trunk of the tree by making spaced cuts around the trunk of the tree with an axe. The cuts should be 5 cm (2 inches) long and spaced with their edges 2.5 to 7.5 cm (1 to 3 inches) apart. Apply 1 to 2 mm (1/32 to 2/32 inch) of the herbicide into each cut using a spray bottle. You can also use this method in conjunction with the girdling method for faster results.
Cut the ash tree down with a chainsaw. Remove lower branches first. Cut a 45 degree angle notch into the tree 1/3 of the way through of the diameter on the side where you want the tree to fall. Cut the second notch at a 45 degree angle at the same depth of the first notch on the other side of the tree, 5 cm (2 inches) higher than the first notch. Saw the second notch until the tree falls the other way.