Glyphosate is a broad-spectrum herbicide used widely in agriculture and landscaping to control unwanted vegetation. While known for eliminating annual weeds and grasses, its effectiveness on large, established woody plants is often questioned. The success of this systemic chemical on trees depends entirely on bypassing the natural defenses of woody tissue and employing specific application methods. This article details glyphosate’s biological function and the precise techniques required for the effective removal of trees and stumps.
The Mechanism of Action
Glyphosate functions as a systemic herbicide, absorbed through foliage or newly cut surfaces and translocated throughout the plant’s vascular system to the growing points. Inside the plant cells, it targets and inhibits the enzyme 5-enolpyruvylshikimate-3-phosphate synthase (EPSP synthase). This enzyme is part of the shikimate pathway, a metabolic route found only in plants and certain microorganisms.
Inhibiting EPSP synthase prevents the plant from synthesizing the three aromatic amino acids: phenylalanine, tyrosine, and tryptophan. These amino acids are necessary for protein synthesis and growth. Their depletion effectively starves the plant of building blocks, causing growth to cease almost immediately. However, visual symptoms, such as yellowing leaves and tissue death, appear more slowly, often taking several weeks to fully manifest.
Specific Effectiveness on Woody Plants
Glyphosate can successfully kill woody plants, but their anatomy presents significant challenges compared to herbaceous weeds, necessitating a modified approach. The thick, waxy cuticle on leaves and the protective bark create a formidable barrier against herbicide absorption. Direct foliar spraying, effective on small weeds, is often ineffective on mature trees because the chemical cannot penetrate the mature tissues in sufficient quantity.
The extensive root system of established trees also requires a higher concentration of the active ingredient for saturation. Since glyphosate travels with the plant’s resources, the most effective time for application is late summer or early fall. During this period, the plant actively moves carbohydrates down to the roots for winter storage. Applying the chemical then ensures maximum translocation to the entire root mass, preventing future resprouting. Symptoms of injury develop slowly, often becoming apparent only after one to two weeks, with the full effect sometimes delayed until the following growing season.
Application Techniques for Tree Removal
To bypass the protective bark and access the tree’s living tissues, specialized application methods focus the herbicide into the cambium layer.
Cut-Stump Treatment
This is one of the most reliable methods, requiring the immediate application of concentrated glyphosate solution to the freshly cut stump surface. The herbicide must be applied within minutes of felling the tree to ensure the vascular system remains open and absorbs the chemical before the cut surface seals.
The solution is painted or sprayed only onto the cambium layer—the thin, moist ring just inside the bark. Treating the central heartwood is unnecessary as it is non-living tissue and will not translocate the herbicide. Failure to treat the entire cambium circumference allows the stump to resprout.
Frill or Hack-and-Squirt Method
This technique is used to kill a standing tree. It involves making a series of downward-angled cuts around the trunk circumference using a hatchet or axe, ensuring each cut penetrates the bark and reaches the sapwood.
A concentrated solution (often undiluted or 50% glyphosate) is immediately squirted into each cut, typically about one milliliter. Cuts should be spaced closely, ideally one cut for every two to four inches of trunk diameter, to ensure distribution throughout the entire vascular ring.
Basal Bark Application
For smaller trees with thin bark, a basal bark application can be used. This involves mixing a specific glyphosate formulation with an oil-based carrier. The mixture is sprayed around the lower 12 to 18 inches of the trunk, completely wetting the bark to the ground line. The oil carrier helps the herbicide penetrate the bark, but this method is most effective on trees less than six inches in diameter with smooth bark.
Minimizing Environmental and Non-Target Impact
Careful application is paramount when using glyphosate for tree removal to prevent damage to desirable plants. The primary risk of non-target damage comes from spray drift, where fine droplets are carried by the wind onto the foliage of nearby ornamental plants. Since glyphosate is highly effective on green tissue, even a small amount of drift can cause severe injury.
For cut-stump and hack-and-squirt applications, the risk of drift is minimized because the chemical is applied directly into the wood. However, care must be taken to prevent runoff onto the soil. Glyphosate binds strongly to soil particles, particularly clay and organic matter, rendering it biologically inactive upon contact with the ground. This strong binding prevents the chemical from being absorbed by nearby plant roots and reduces the risk of leaching into groundwater.
The breakdown of glyphosate in the soil is primarily mediated by microbial activity, with an average half-life estimated around 30 days in temperate climates. The primary metabolite, aminomethylphosphonic acid (AMPA), can persist slightly longer. To protect pets and humans, keep them away from the treated area until the herbicide solution has fully dried and been absorbed into the wood.