Glufosinate-ammonium is a widely used broad-spectrum herbicide in agriculture, playing a significant role in weed management across various cropping systems.¹ Here's a detailed look at its uses, mechanism, and considerations:

What is Glufosinate-Ammonium?

Glufosinate-ammonium is a naturally occurring broad-spectrum herbicide derived from soil bacteria (Streptomyces viridochromogenes).² It is a non-selective, contact herbicide, meaning it affects most plants it comes into contact with, and its primary action occurs where it is applied, with limited systemic movement within the plant.³

Mechanism of Action

Glufosinate-ammonium works by inhibiting the enzyme glutamine synthetase (GS).⁴ This enzyme is crucial for plants because it catalyzes the synthesis of glutamine from glutamate and ammonia, playing a central role in nitrogen metabolism and ammonia detoxification.⁵

When glufosinate-ammonium inhibits GS:

• Ammonia accumulation: It leads to a rapid and toxic buildup of ammonia within plant cells. Ammonia is toxic to plants at high concentrations.⁶
• Disruption of photosynthesis: The accumulation of ammonia disrupts the thylakoid membranes in chloroplasts, uncoupling photophosphorylation, which is essential for photosynthesis.
• Cell death: The combination of ammonia toxicity and impaired photosynthesis leads to the rapid desiccation and death of the plant.

Symptoms of glufosinate-ammonium application typically appear within 2-4 days, with complete weed death occurring in about 7-10 days.

Agricultural Uses

Glufosinate-ammonium is used in various agricultural scenarios:

1. Broad-Spectrum Weed Control: It effectively controls a wide range of annual and perennial broadleaf weeds and grasses.⁷ This includes difficult-to-control glyphosate-resistant weeds like amaranthus, lolium, conyza, and malva.
2. Genetically Modified (GM) Crops: A major application of glufosinate-ammonium is in crops genetically engineered to be tolerant to it.⁸ These include:
   • Glufosinate-tolerant corn
   • Glufosinate-tolerant soybeans
   • Glufosinate-tolerant canola⁹
   • Glufosinate-tolerant cotton This allows for post-emergence application of the herbicide directly to the crop field, controlling weeds without harming the cultivated crop.
3. Directed Sprays/Orchards/Vineyards/Non-Crop Land: Since it's a contact herbicide, it can be used as a directed spray around the base of trees, vines, and bushes in orchards (e.g., fruit trees, nuts, olives) and vineyards to control weeds without affecting the main plant.¹⁰ It's also used for total vegetation control on non-cultivated land.¹¹
4. Desiccant: Glufosinate-ammonium can be used as a desiccant to dry down crops like potatoes and sunflowers before harvest, facilitating mechanical harvesting.¹²
5. Sucker Control: In some crops, like vines and certain trees, it can be used to control suckers (new shoots emerging from the roots) without harming the mother plant.¹³
6. Conservation Tillage Systems: Its effectiveness as a burndown herbicide (applied before planting or crop emergence) makes it valuable in reduced or no-till farming systems.¹⁴ This helps preserve soil structure, reduce erosion, and conserve moisture.¹⁵
7. Disease Suppression: Some studies suggest glufosinate-ammonium can offer some protection against certain plant diseases, such as rice sheath blight, due to its antifungal and antibacterial properties.¹⁶

Advantages in Agriculture

• Unique Mode of Action: Its distinct mode of action (inhibition of glutamine synthetase) makes it a valuable tool for managing herbicide resistance, particularly to glyphosate-resistant weeds.
• Fast-Acting: Visible results (yellowing and wilting) appear quickly, usually within days.
• Contact Activity: Its contact nature allows for precise weed control without affecting the roots of desirable plants, making it suitable for applications around established crops.¹⁷
• Rapid Soil Degradation: Glufosinate-ammonium degrades relatively quickly in soil through microbial action, minimizing the risk of groundwater contamination.¹⁸

Safety and Environmental Considerations

• Operator Safety: When handling glufosinate-ammonium, it's crucial for farmers and applicators to wear appropriate personal protective equipment (PPE), including gloves, protective clothing, eye protection, and respirators, to avoid direct skin contact and inhalation.
• Environmental Fate: While it degrades rapidly in soil, proper application techniques are essential to prevent off-target movement via spray drift, which can harm non-target plants. It's recommended to apply when wind speeds are low and use appropriate nozzle types for optimal coverage.
• Mammalian Toxicity: Studies generally indicate low acute toxicity to humans and mammals.¹⁹ However, high doses can lead to neurological effects in laboratory animals.²⁰ Residues in food are monitored and regulated, with safety factors applied.²¹
• Reproductive Concerns: Some studies have raised concerns about potential reproductive toxicity and neurotoxicity, especially with prolonged exposure, which has led to its ban in some regions (e.g., EU member countries).²² It is important to adhere to local regulations and guidelines for its use.

Resistance Management

To prevent the development of weed resistance to glufosinate-ammonium and maintain its efficacy, integrated weed management (IWM) strategies are highly recommended:

• Herbicide Rotation: Rotate glufosinate-ammonium with herbicides that have different modes of action.²³ This prevents over-reliance on a single herbicide group.
• Tank Mixing: Use glufosinate-ammonium in tank mixes with other herbicides that have different modes of action to broaden the spectrum of control and reduce selection pressure.²⁴
• Cultural Practices: Incorporate non-herbicide weed control methods such as:
  • Crop rotation
  • Tillage (where appropriate)
  • Cover cropping
  • Timely planting
  • Optimized crop density
• Early Intervention: Control weeds when they are small and actively growing for maximum effectiveness, preventing them from setting and shedding seeds.
• Monitoring: Regularly scout fields to monitor weed populations and identify any potential signs of resistance development.²⁵

In summary, glufosinate-ammonium is a powerful and versatile herbicide in modern agriculture, particularly valuable for its unique mode of action and efficacy against a wide range of weeds, including those resistant to other herbicides.²⁶ However, its effective and safe use requires adherence to label instructions, proper application techniques, and integration into a comprehensive weed management program to prevent resistance and minimize environmental and health risks.²⁷