Mode of Action

• Every herbicide has its own mode of action by means of which it kills plants and weeds. The biochemical or physical mechanism kills plants by interrupting their metabolic processes. Some do not directly interfere with metabolic processes but leak out essential cellular contents by inflicting damage on cell membranes. Some species or whole groups of plants may not be exterminated by certain herbicides because they use different biochemical or mechanical pathways. An herbicide is selected based on its specific mode of action. For instance, pre-emerged herbicides are formulated to kill weeds at their germination stages, while post-emerged herbicides are normally applied 'post' or after germination of the weeds.
  
  

Formulations

• Herbicides are available in different forms (i.e., liquid formulations, dry formulations, and salts and esters). They often contain ingredients, surfactants, solvents, dyes, carriers and additives which improve stability and usefulness. Spray or liquid formulations are highly soluble in water. Dry formulations consist of granules or coarse particles. Dry formulations remain effective for longer periods of time and are often used in soil applications. Many herbicides consist of acids which can be prepared as a salt or ester for application.
  
  

Mechanisms of Dissipation

• Dissipation means the immobilization, degradation and movement of an herbicide in the environment. Immobilization sets apart the herbicide and keeps it from moving in the environment. Degradation takes place when an herbicide breaks down to smaller molecules producing carbon dioxide, water and salts. An herbicide moves through an environment by surface run-off and evaporation from soil and plant surfaces.
  
  

Behavior in the Environment

• Water solubility of an herbicide is one of the most important factors in the environment. Water-soluble herbicides are transportable, therefore readily available for microbial metabolism and other degradation processes.
  
  

Environmental Toxicity

• Every herbicide is more or less toxic to all living organisms, especially to aquatic life. Additives like diesel fuel and methanol used in the manufacturing process could be more toxic than the active ingredients in the herbicide.