What indicates that a contact herbicide is working?

The indication that a contact herbicide is working is shown when the plant begins to yellow and wilt in the contact areas. Contact herbicides are designed to destroy the plant tissue they come into contact with, leading to visible signs of damage such as yellowing, wilting, or browning of the leaves and stems. This response occurs as the herbicide disrupts the plant’s cellular functions, ultimately leading to its death.

In contrast, if the treated area remains green and healthy, it suggests that the herbicide has not effectively penetrated or impacted the plant tissue. The appearance of new growth on the plant would indicate that it is healthy and potentially thriving, which contradicts the intended purpose of a contact herbicide. Similarly, if the plant grows faster after treatment, it implies that the herbicide is not functioning as expected, allowing the plant to continue its growth unchecked.