Which of the following practices helps in preventing the spread of broadleaf weeds?

Overseeding as a method for thickening turf is an effective practice for preventing the spread of broadleaf weeds. When you overseed, you introduce more desirable grass species into the lawn. This enhances the overall density of the turf, which creates a competitive environment that is less favorable for weeds. Thicker turf can shade the soil more effectively, reducing the sunlight available for weed seeds to germinate and grow. Additionally, a denser turf can crowd out existing weeds, making it challenging for them to establish and thrive.

Other practices, such as regular low mowing, heavy irrigation, and using high nitrogen fertilizers, do not effectively prevent broadleaf weeds. Regularly mowing low can stress the grass and may not contribute significantly to weed prevention. Heavy irrigation can actually create a more favorable environment for weed growth by providing adequate moisture for germination. High nitrogen fertilizers can encourage rapid growth of grass, but they can also promote the growth of weeds, particularly broadleaf varieties, if not managed properly. Thus, overseeding is a proactive approach that addresses weed competition right at the turf's growth level.