A preemergent herbicide is best described as:

• A. Kills Mature Weeds After They Have Grown
• B. Is Selective For Dicots Only
• C. Is Nonselective And Kills All Vegetation
• D. Prevents Seeds From Germinating; Lasts Weeks To Months; Must Be Applied Before Seeds Germinate

Answer: (D)

A preemergent herbicide acts in the soil before weed seeds germinate, forming a chemical barrier that prevents germination or the establishment of seedlings. Because it needs to be present as seeds begin to sprout, it must be applied before seeds germinate, and its effect can persist for weeks to months depending on the product, soil, and weather. This is why the statement describing it as preventing seeds from germinating, lasting weeks to months, and requiring application before germination is the best fit.

Killing mature weeds after they have grown describes a postemergent approach, which targets weeds after they’ve already emerged. Being selective for dicots only is not a universal trait of preemergents, as many are not limited to dicots. Being nonselective and killing all vegetation would describe a nonselective herbicide, not the defining feature of a preemergent.