How to Kill a Tree Using Herbicides

Sometimes a tree just needs to go!
Good news is, you can chemically treat and kill trees in an environmentally safe way if you follow the chemical label recommendations. Some treatments apply herbicide to a specific area on the tree. These applications will reduce impacts on adjacent vegetation from drift or overspray. But other methods require complete herbicide coverage on foliage or soil - a bit more complicated.
Here are the most effective available chemical methods used to kill trees.

Bark on larger diametered trees need a direct pathway for herbicide entry into the plant's vascular tissue. Do this by making a series of downward cuts through the bark, leaving the frill connected to the tree. Make these cuts around the entire circumference of the tree trunk with an axe or hatchet. Immediately apply the selected herbicide into the cuts. Avoid spring applications when sap flowing out of the wound will prevent good absorption.

This is similar to cut surface treatments. Use specialized tree injection equipment to administer a specific amount of herbicide into the tree when the cut is made. Treatments are effective when injections are made every 2 to 6 inches around the tree. For best results, treat trees 1.5 inches or more diameter at chest height.

You actually cut a tree down and treat the freshly cut surface with herbicide. On larger trees treat only the outer 2 to 3 inches, including the cambium layer, of the stump (the internal heartwood of the tree is already dead). On trees 3 inches or less in diameter, treat the entire cut surface. Apply treatments immediately after cutting to achieve maximum effectiveness.

Apply the herbicide to the lower 12 to 18 inches of the tree trunk from early spring to mid-fall. Some species can be treated during winter. Use herbicide spray mixed with oil, until the bark is saturated. The low volatile ester formulations are the only oil soluble products registered for this use. This method is effective on trees of all sizes.

Foliar spraying is a common method of applying herbicides to brush up to 15 feet tall. Make applications from early summer to late September, depending on choice of herbicide. Treatments are least effective during very hot weather and when trees are under severe water stress. Except in very sensitive species, spraying plants with rapidly elongating stems will often result in excessive sprouting. Saturation of the tree is not necessary.

Certain soil treatments applied evenly to the soil surface move into the root zone of the targeted plants after ample rainfall or overhead moisture. Banding (also called lacing or streaking), applies concentrated solution to the soil in a line or band spaced every 2 to 4 feet. Use this type of application to kill large numbers of trees.

Tip #1
Remember - call your local Cooperative Extension Service for detailed chemical information pertaining to any chemical treatments used. You are responsible for the chemicals you use and their ultimate effects.

Tip #2
Remember - plants use suberizationas a natural healing process. Suberization occurs by adding a layer of protective "corky" cells over the damaged tissue. These cells can reduce herbicide effectiveness by preventing absorption. When using frilling or cut stump methods of treatment, apply the herbicide immediately to achieve maximum absorption.

Tip #3
Remember - roots of plants can share vascular tissue through root grafting. Root grafting occurs primarily within the same species but may occur between plants within the same genus. Your herbicide can move from a treated tree to an untreated tree, killing or injuring it.

Tip #4
Remember - once the herbicide is released from a tree, it can be available for uptake by another. This is called flashback. The serious consequence of this is that a treated tree may release herbicide back into the environment, injuring other nearby trees and vegetation.

Tip #6
Remember - adding stains or dyes to the herbicide solution substantially increases applicator accuracy. Applicators use the dyes to monitor treated trees, so they are less likely to miss or respray targeted trees. Use of stains can also indicate personal exposure.

Tip #7
Remember - dripline is the area directly underneath the tree canopy. Herbicide labels frequently caution against making applications within the dripline of desirable trees. But tree roots often extend well beyond the dripline. Use the rule-of-thumb that tree roots extend a distance equal to the height of a tree growing east of the Cascades, and equal to half of the height for a tree growing west of the Cascades.

Tip #8
Remember - you can control weed-trees without using chemicals. See: Kill Trees Without Chemicals