Why might weeds still appear in a managed lawn like Mrs. Zimmerman's?

The correct answer is that wind and birds may carry seeds into the yard. In a managed lawn, even with diligent maintenance and pest management practices in place, new weeds can be introduced into the environment through natural processes. Wind can easily transport lightweight seeds over long distances, while birds often consume seeds and later deposit them in different locations through their droppings. This means that even if a lawn is well-maintained, it is still subject to external factors that can lead to the emergence of new weeds.

In contrast, while it is true that some weeds can develop resistance to herbicides, this is not the primary reason for their appearance in a managed lawn. Additionally, weeds growing faster than they can be managed suggests limited time or resources for maintenance rather than an inevitable outcome in a managed environment. Frequent watering may create optimal growth conditions for both desirable grass and undesirable weeds, but it is not the sole reason for their appearance; other factors like seed dispersal play a critical role. Thus, the influence of external seed sources through natural means is a key reason weeds might still infiltrate a managed lawn such as Mrs. Zimmerman's.