Which of the following is a mechanical control strategy for weeds?

Mowing height adjustments are considered a mechanical control strategy for weeds because they involve physical manipulation of the plant environment to manage weed growth. By adjusting the height at which grass or crops are mowed, you can effectively suppress weeds. For example, mowing at the right height can prevent certain weed species from flowering and producing seeds, thus reducing their population over time. This method is hands-on and does not rely on chemical interventions, making it a purely mechanical approach.

In contrast, slicing with a knife is typically not a widespread method for controlling weeds and may not provide a comprehensive solution. Applying fertilizer is a form of chemical or nutrient management rather than a mechanical control, as it aims to promote the growth of desired plants rather than physically alter the conditions for weeds. Excessive watering can lead to favorable conditions for both desired plants and weeds, and is not a direct mechanical approach to weed management.