Which of the following pesticides is known to kill grasses but not broadleaves?

Clethodim is a herbicide that specifically targets grasses while leaving broadleaf plants unharmed. It operates as a selective herbicide, meaning it can be used in environments where grass control is needed without negatively affecting other types of vegetation. This characteristic makes it especially useful in various agricultural and landscape management scenarios where it is important to control certain grass species without impacting the growth and health of broadleaf plants.

In contrast, glyphosate is a non-selective herbicide that kills all actively growing plants, including both grasses and broadleaves. Metolachlor is primarily used for controlling annual grasses and some broadleaves but does not possess the same selectivity as Clethodim. Triclopyr is designed for the control of woody plants and broadleaf weeds, but it is not effective against grasses. Therefore, Clethodim is the best choice for achieving the desired outcome of killing grasses without harming broadleaf plants.