Greenbrier (Smilax) is a persistent, thorny, woody vine common across much of North America, often known as catbrier or prickly-ivy. It rapidly forms dense, impenetrable thickets. Standard weeding or simply cutting the above-ground vines rarely achieves long-term control. Effective management requires targeted strategies utilizing herbicides designed to attack the plant’s robust underground structure.
Understanding Greenbrier’s Resilience
The difficulty in eliminating greenbrier stems from its extensive and deep root system, which consists of knobby, tuberous rhizomes. These rhizomes function as significant storage organs, accumulating large reserves of energy and carbohydrates over the growing season. Even if the visible vines and leaves are completely destroyed, the plant can rapidly re-sprout using the stored energy within these underground tubers. The woody stems and waxy coating on mature leaves further protect the plant, making it difficult for surface-applied herbicides to penetrate and translocate to the roots. To achieve complete control, a management strategy must deliver a concentrated herbicide deep into this reservoir of energy.
Recommended Herbicide Active Ingredients
The most effective chemical control for greenbrier relies on systemic herbicides, which are absorbed by the plant and moved internally to the root system. The two primary active ingredients recommended for controlling these woody vines are triclopyr and glyphosate.
Triclopyr is a selective, synthetic auxin herbicide that mimics natural plant growth hormones, causing uncontrolled and disorganized growth that ultimately kills the plant. The ester formulation of triclopyr is superior for woody plants because it is oil-soluble, allowing it to penetrate the waxy leaf cuticles and woody bark more effectively than water-soluble amine formulations.
Glyphosate is a non-selective, systemic herbicide that inhibits an enzyme necessary for the plant to produce essential proteins, leading to plant death. For effectively killing the deep root system, a highly concentrated formulation is necessary, typically 41% active ingredient or higher, especially for cut-stump applications.
An additional ingredient, 2,4-D, is sometimes used in combination products with triclopyr for foliar application. However, 2,4-D alone often lacks the necessary strength to control established, mature greenbrier.
Specialized Application Techniques
Successful greenbrier control depends entirely on using specialized application methods that bypass the plant’s defenses and deliver the active ingredient directly to the root system. The most reliable method for established, large-diameter vines is the cut-stump technique.
Cut-Stump Technique
This involves cutting the vine close to the ground, leaving a short stump, and immediately applying a concentrated herbicide solution. The herbicide must be applied within minutes to the actively transporting tissues, specifically the cambium layer, which is the ring just inside the bark. A concentrated solution (often 20% to 50% glyphosate or undiluted triclopyr) is painted or dripped onto this outer ring to ensure translocation to the roots. This highly focused application is effective throughout the year, though late summer through early winter is optimal when the plant naturally moves resources to its roots.
Foliar Application
Foliar application, where the leaves are sprayed, is typically reserved for dense patches of young, actively growing greenbrier or for re-sprouts. This method requires a surfactant, a chemical additive that helps the herbicide solution penetrate the naturally waxy leaf surface. Timing is important for foliar sprays, with late summer or early fall being the most effective period, as the plant is actively moving sugars and the herbicide down to its roots for winter storage.
Basal Bark Treatment
An alternative approach for standing, woody stems is the basal bark treatment. This uses an oil-soluble triclopyr ester mixed with a penetrating oil carrier, such as basal oil. The mixture is sprayed around the entire circumference of the lower 12 to 18 inches of the stem, allowing the oil to carry the herbicide through the bark.
Non-Chemical Removal Methods
For those who prefer to avoid chemical treatments, manual removal remains an option, though it requires significant effort and persistence. The primary goal of non-chemical control is the complete physical removal of the entire underground root system. This means digging out the extensive, knobby rhizomes and tubers, which can be challenging. Any piece of the tuber left in the soil can potentially re-sprout, necessitating thorough and deep excavation.
For widespread infestations, the most practical non-chemical approach is the “starvation method.” This involves repeatedly cutting the new shoots and vines back to the ground as soon as they appear. By consistently removing the above-ground foliage, the plant is prevented from photosynthesizing and replenishing its carbohydrate reserves, eventually exhausting the root system over several seasons.