What does a contact herbicide do?

A contact herbicide is specifically formulated to affect only the parts of the plant that it directly comes into contact with when applied. This means that its action is localized to the area that is sprayed, rather than being systemically absorbed and transported throughout the plant via its vascular system.

When a contact herbicide is applied to leaves or stems, it begins to work by disrupting specific processes in those tissues, causing damage or death to the plant. This characteristic makes contact herbicides effective for treating visible weeds without affecting the surrounding soil or roots, which is reflected in the correct answer.

In contrast, systemic herbicides are absorbed and transported within the plant, which allows them to work on the root system and produce longer-lasting effects. Additionally, options that mention soil penetration or long-term residual effects do not apply to contact herbicides, as their efficacy relies on direct application to the targeted plant parts rather than residual activity in the soil or root absorption.