Which of the following is an example of biological control?

Biological control refers to the use of natural organisms, such as predators, parasites, or pathogens, to manage pest populations in a way that is environmentally friendly. The cut-stump technique, primarily used in the context of controlling invasive plant species, can be classified as a form of biological control when it involves applying herbicides or biological agents to the cut surface of a plant. This method prevents the unwanted plant from regenerating, allowing beneficial native plants or ecological balance to be restored in an area.

In contrast, soil fertilization enhances soil productivity but does not specifically target pest organisms; mechanical weeding involves physical removal of plants and does not utilize biological agents against pests; and mass planting of non-native species could lead to ecological imbalances, as it could promote invasive non-native species rather than controlling pests in a beneficial way. Therefore, the cut-stump technique stands out as the example of biological control among the options provided.