Which of the following is a common result of applying postemergence herbicides?

Postemergence herbicides are designed to target and control weeds that have already emerged and are growing in a specific area. When applied, these herbicides often exhibit variations in effectiveness based on the growth stage and type of the weed. In many cases, they may be less effective on established weeds that are robust and have developed extensive root systems and foliage.

Established weeds can be more resilient and better able to withstand the effects of herbicides, making it challenging for the chemicals to penetrate and be effective. The timing of application is key, as young, actively growing weeds are usually more susceptible to postemergence herbicides than those that have matured.

The other options do not accurately reflect the characteristics of postemergence herbicides. They do not require incorporation into the soil for effectiveness, as they act on the foliage. They are also formulated to target specific plants rather than soil pathogens, and their primary function is not to prevent seed germination but rather to kill actively growing weeds. Understanding these distinctions helps explain why the selected answer is the most accurate representation of postemergence herbicides' effects.