Glyphosate: A Systemic, Non-Selective Herbicide
Introduced in 1974, glyphosate is the world’s most-used herbicide, introduced in 1974. It is a Group 9 (EPSPS inhibitor) herbicide that operates as a non-selective, systemic, post-emergent product to control actively growing green plants, including grasses, broadleaves, and sedges.
- Active class: Non-selective & systemic herbicide
- Herbicide group: Group 9 (EPSPS Inhibitor)
- Common formulations: Sold as Roundup® & generics (IPA, potassium, diammonium salts)
- Target: Enzymes found only in plants & microbes—not humans/animals
- Why it matters on your farm: Controls emerged Palmer amaranth & other tough weeds—but won't stop the next flush.
Always read and follow the herbicide label. This handout is for general educational use and does not replace label directions or product-specific guidance.
What is glyphosate?
Glyphosate is a broad-spectrum, post-emergent herbicide that controls nearly all actively growing green plants, including grasses, broadleaves, and sedges. It targets an enzyme found only in plants and microbes, meaning it does not target humans or animals. It is commercially available as Roundup® and various generic formulations using isopropylamine (IPA), potassium, or diammonium salts. Glyphosate provides no soil residual, which means it will not stop new weeds from emerging.
What is the mode of action?
Foliar uptake → Phloem translocation → ESPS enzyme blocked → Shikimate pathway halted → Plant death (7-14 days)
- Glyphosate is absorbed only through green tissue, not roots or soil.
- It moves with sugars (phloem) to roots and growing points.
- It blocks EPSPS enzyme, halts 3 essential amino acids.
- Symptoms: Yellow and then brown and wilt of 1-3 weeks, but happens more slowly when cool.
What are the chelating characteristics?
Chelates (binds) metal ions: Ca2+, Mg2+, Fe3+, Mn2+
- Spray tank: Hard-water cations bind glyphosate first, cutting efficacy.
- Soil: Same binding locks glyphosate onto clay and metal oxides.
- Field fix: Add AMS (4-17 lb/100 gal) before glyphosate. Sulfate ties up cations, keeping glyphosate active.
Residual effects and soil behavior
- Soil activity: Minimal, not a pre-emergent, binds tightly to soil.
- Soil half-life: About 3-130+ days dependent on soil type, microbes and moisture.
- Mobility: Low leaching, tightly soil-bound.
- Breakdown: Mainly soil microbes, not sunlight or water.
- Replant interval: No residual-based restriction, but should confirm using the product label.
Maximizing efficacy in the field
Follow these field guidance steps to maximize product efficacy and manage resistance.
- Treat weeds when they are small and actively growing (rosette–early bolt).
- Use clean water; add AMS if water hardness is >300 ppm.
- Match nozzle and pressure settings for full coverage while minimizing drift.
- Spray in warm, sunny conditions with low wind; avoid rainfall within 4–6 hours of application.
- Check tank-mix compatibility to avoid antagonism.
- Rotate modes of action (MOAs) to manage herbicide resistance (e.g., Palmer amaranth).
- Avoid applying to drought-stressed weeds, as this leads to poor uptake.