Glufosinate and glyphosate are two of the most widely used broad-spectrum, non-selective herbicides in global agriculture. Both chemicals are highly effective at controlling a wide range of weeds. Although both are designed to eliminate unwanted plant life, they possess distinct chemical structures and function through fundamentally different biological pathways inside the plant. Understanding the differences in their mechanism of action, application methods, and environmental profiles is necessary for effective weed management in the agricultural industry.
Fundamental Differences in Mechanism of Action
Glyphosate works by interfering with the shikimate pathway, a biochemical route found exclusively in plants, bacteria, and fungi. Specifically, glyphosate acts as a competitive inhibitor of the enzyme 5-enolpyruvylshikimate-3-phosphate synthase (EPSP synthase). By binding to and blocking this enzyme, the plant is unable to synthesize the three essential aromatic amino acids: phenylalanine, tyrosine, and tryptophan. Without these necessary building blocks for protein synthesis, the plant’s growth halts, and it slowly dies over a period of days or weeks.
Glufosinate, conversely, targets the nitrogen assimilation process by inhibiting the enzyme glutamine synthetase. This ubiquitous enzyme plays a crucial role in converting the toxic byproduct ammonia into the non-toxic amino acid glutamine. When glufosinate inhibits this enzyme, ammonia rapidly builds up to toxic levels within the plant cells, disrupting cellular functions like photosynthesis. This toxic accumulation of ammonia triggers a much faster onset of plant death compared to the slower action of glyphosate.
Application Strategies and Resistance Management
Glyphosate is a systemic herbicide, meaning it is absorbed by the foliage and then translocated throughout the entire plant, including the roots and underground storage organs. This systemic movement makes it effective for controlling established, deep-rooted perennial weeds, as the chemical can reach and kill the entire plant structure. Because of its systemic nature, glyphosate is slower-acting, often taking one to two weeks for visual symptoms to become apparent.
Glufosinate functions as a contact herbicide, meaning it only kills the plant tissue it physically touches. This contact action results in a much faster kill, with visible damage like wilting and necrosis typically appearing within one to three days of application. Its limited translocation makes it less effective against large, mature perennial weeds, requiring more thorough spray coverage. Glufosinate also lacks residual activity, breaking down quickly and having no carryover effect in the soil, which often requires follow-up treatments.
The development of genetically modified crops plays a large role in the application of both herbicides. Crops engineered with the CP4 EPSPS gene are tolerant to glyphosate (known commercially as Roundup Ready crops), allowing the herbicide to be sprayed directly over the growing crop. Similarly, Glufosinate-resistant crops contain the pat or bar gene, which detoxifies glufosinate. The rapid evolution of weeds resistant to glyphosate has elevated glufosinate to a valuable tool in modern resistance management strategies. Farmers rotate the use of these two herbicides to avoid relying on a single mode of action and slow the spread of resistant weed populations.
Environmental Persistence and Human Health Profile
Environmental Persistence
Glyphosate exhibits strong binding to soil particles, which limits its movement through the soil profile and reduces the risk of leaching into groundwater. Its primary breakdown product, aminomethylphosphonic acid (AMPA), can be more persistent in the environment than the parent compound. Glufosinate generally degrades more rapidly in soil and water through microbial action, resulting in minimal residual activity and a lower potential for long-term soil persistence. This rapid breakdown is one reason glufosinate is often considered safer for crop rotation.
Human Health Profile
Glyphosate has been the subject of significant public and scientific debate. In 2015, the International Agency for Research on Cancer (IARC) classified glyphosate as “probably carcinogenic to humans” (Group 2A). However, major regulatory bodies, including the U.S. Environmental Protection Agency (EPA) and the European Food Safety Authority (EFSA), have concluded that glyphosate is unlikely to pose a carcinogenic risk to humans when used according to label instructions. Glufosinate has a profile of low acute toxicity to mammals, and its rapid environmental degradation generally limits the potential for chronic exposure.