What describes a contact herbicide's action?

A contact herbicide acts directly on the plant parts that it comes into contact with, which means it kills or stunts only those specific areas. This type of herbicide does not penetrate deeply into the plant structure or system, making its effects localized to the tissue that has been sprayed. For instance, if a contact herbicide is applied to the leaves of a weed, it will only affect the foliage exposed to the product and will not impact the roots or other parts of the plant that were not sprayed. Therefore, any plant growth or regenerations from untreated parts will remain unaffected.

In contrast, systemic herbicides are those that are absorbed by the plant and can move throughout its entire system, affecting all parts, which is not the case for contact herbicides. Additionally, while some herbicides may not be effective on certain species, such an attribute does not define the action of a contact herbicide specifically. Lastly, contact herbicides do not promote the growth of desirable plants; their purpose is to eliminate unwanted vegetation.