The term "herbicide" does not specifically refer to paraquat; they belong to different categories. Herbicides are a general term for pesticides used to eliminate or inhibit weed growth. Their mechanisms of action encompass various technical pathways, including contact, systemic, and hormonal types, achieving their weed-killing effect by interfering with plant physiological processes such as photosynthesis, cell division, or protein synthesis. Paraquat (chemical name: 1,1'-dimethyl-4,4'-bipyridine cationic herbicide) is only one specific chemical component of herbicides. It was once widely used due to its rapid contact killing and non-selective nature (capable of killing most green plants). However, because of its extremely high toxicity to humans (the lethal oral dose is approximately 5 ml) and the lack of a specific antidote, my country banned the sale and use of paraquat aqueous solutions in 2016 and completely banned the production of paraquat soluble formulations in 2020. Currently, only a very few formulations are permitted for limited use in specific scenarios.
From a technical perspective, modern herbicides have developed into a diversified system of components. For example, glyphosate kills weeds through systemic absorption by inhibiting the synthesis of aromatic amino acids in plants; glufosinate-ammonium causes cell death by inhibiting glutamine synthase; and hormone-type herbicides such as 2,4-D cause abnormal growth by interfering with plant hormone balance. These components differ significantly in toxicity, residual period, and applicable crops. Taking glufosinate-ammonium as an example, its toxicity is far lower than paraquat (the acute oral LD50 in rats is approximately 2000 mg/kg, while paraquat is 150 mg/kg), and it is easily degraded in soil, making it safer for subsequent crops.
Regarding application scenarios, the selection of herbicides needs to comprehensively consider factors such as crop type, weed species, and environmental conditions. For example, for weed control in non-arable land, formulations containing glufosinate can be used. A 200g/L formulation can treat approximately 200 square meters, achieving over 90% control efficacy against annual weeds. For farmland weed control, selective herbicides should be chosen based on the crop's sensitive growth period. For instance, in cornfields, a combination of nicosulfuron and atrazine can precisely control barnyard grass, foxtail, and other grassy weeds. The industry standard (GB/T 31754-2015, "General Technical Requirements for Herbicides") clearly stipulates that herbicides must be labeled with key information such as the active ingredient, content, formulation, scope of application, and safety interval. Users should strictly verify the labels when purchasing herbicides.
It is particularly important to note that the development of alternatives to paraquat has become a key focus in the industry. For example, the low-toxicity diquat dichlorvos, through optimized molecular structure, maintains rapid contact killing properties while reducing acute oral toxicity to 500mg/kg (rat), and significantly reduces eye and skin irritation. In addition, biological herbicides such as bisphosphonate (a natural compound derived from Streptomyces) have broad application prospects in organic agriculture due to their environmental friendliness.
