Which type of herbicide forms a barrier in the soil to prevent weeds from germinating?

A pre-emergence herbicide is specifically designed to create a barrier in the soil that inhibits weed seeds from germinating. This type of herbicide acts before the weeds emerge, targeting the early stages of the weed life cycle. By applying a pre-emergence herbicide, you effectively disrupt the process of germination, preventing the seeds from developing into mature plants.

The mechanism of action involves the herbicide being absorbed by the seeds as they attempt to germinate. This provides a protective effect over a certain period, allowing for control of various types of annual weeds. Pre-emergence applications are typically made at strategic times, often in relation to local weather patterns, to coincide with the germination of weeds.

In contrast, post-emergence herbicides are used to control weeds after they have already emerged and established. Residual herbicides also target existing weeds but may provide longer-lasting control in the soil. Systemic herbicides are absorbed by plants and move through their systems to destroy them. Each type has its specific use case, but only pre-emergence herbicides are designed to form a barrier against germination.