What type of herbicides control grasses and certain broadleaves?

The correct choice is preemergence herbicides, which are specifically designed to prevent the germination of weed seeds, including certain grasses and broadleaves, before they can emerge from the soil. These herbicides work by creating a chemical barrier in the soil that inhibits the development of seedlings, effectively controlling unwanted plant growth during their initial stages.

Preemergence herbicides are often applied to the soil before the target weeds germinate, making them particularly useful in managing weed populations in various settings, such as agricultural fields and landscapes. This proactive approach to weed management helps reduce competition for resources like sunlight, water, and nutrients that would otherwise be taken by the unwanted plants.

While postemergence herbicides are effective for controlling existing weeds that have already emerged, they do not prevent new weed seeds from germinating. Desiccants are used to accelerate the drying process of plants but are not targeted specifically at preventing weed growth. Systemic herbicides move throughout the plant's system to kill it entirely, but again, they won't prevent weed seed germination.

This distinction in the functional application of herbicides highlights why preemergence herbicides are the most appropriate choice for managing both grasses and certain broadleaf weeds before they appear above ground.