How herbicide auxin works — illustrated mechanism of action
Triclopyr is the go-to herbicide for killing woody plants, brush, stumps, and vines that 2,4-D cannot handle. It excels at killing poison ivy, wild blackberry, kudzu, woody brush, and tree stumps. Available in both amine (Garlon 3A) and ester (Garlon 4 Ultra) formulations.
How herbicide auxin works — illustrated mechanism of action
Woody brush, poison ivy and poison oak (excellent), wild blackberry, kudzu, multiflora rose, honeysuckle, buckthorn, privet, tree stumps (cut-stump treatment), woody vines. Also controls broadleaf weeds in lawns but 2,4-D is usually preferred for that purpose due to cost.
Crossbow (Corteva - triclopyr + 2,4-D, the most popular brush killer), Garlon 3A (amine, professional), Garlon 4 Ultra (ester, professional), Ortho Brush-B-Gon, BioAdvanced Brush Killer Plus, Remedy Ultra (Corteva, rangeland). Cut-stump treatment formulations also available.
Moderate toxicity. Ester formulations are more irritating than amine. Wear long sleeves, gloves, and eye protection during mixing and application. Toxic to fish - do not apply near water bodies. Observe buffer zones.
For poison ivy: Triclopyr is the most effective herbicide for poison ivy. Apply Crossbow or Garlon to actively growing leaves in late spring/early summer. Full coverage of leaf surfaces is critical. Expect die-back within 2-4 weeks. Large established patches may need a second application.
Cut-stump treatment: For killing tree stumps and preventing regrowth, cut the tree and immediately (within 5 minutes) paint the cut surface with undiluted triclopyr ester (Garlon 4 Ultra). The herbicide travels down through the vascular system to kill the roots. Wait too long and the cut surface seals over.
For brush clearing: Crossbow (triclopyr + 2,4-D) applied as a foliar spray to actively growing brush is the standard professional approach. Use a pump sprayer or backpack sprayer with a flat fan nozzle for even coverage. Apply until leaves are wet but not dripping.
Selective in lawns: Triclopyr controls broadleaf weeds that 2,4-D misses, particularly ground ivy (creeping charlie) and wild violets. Some lawn herbicide products include triclopyr for this reason.