By far the most effective way to control weeds on a farm is to use herbicides. Herbicides can be used in conjunction with other weed-control methods, such as tillage, but they are most effective when used alone. There are two main types of herbicides: pre-emergent and post-emergent. Pre-emergent herbicides are applied before the weeds germinate, while post-emergent herbicides are applied after the weeds have germinated. There are also several different types of herbicides, each of which works differently. Some kill the weed directly, while others inhibit its growth.

By spraying Round Up. Roundup is a herbicide that kills weeds by inhibiting the plant enzyme 5-enolpyruvylshikimate-3-phosphate synthase (EPSP synthase), which is involved in the synthesis of aromatic amino acids. Weeds can be controlled on a farm in a number of ways, but using Round Up as a herbicide is one of the most effective and common methods.