Which method can enhance seed set in self-pollinated plants?

Enhancing seed set in self-pollinated plants can be significantly impacted by the interaction with pollinators, as indicated by the correct choice. While self-pollinated plants are capable of fertilizing themselves without the need for external insects, the visits from pollinators can help improve the efficiency of this process. Pollinators can transport pollen from a plant's anthers to its stigma more effectively than pollen falling by gravity alone, potentially increasing not only the seed set but also the genetic diversity of the offspring. Even in self-pollinated plants, the influence of pollinators can lead to better pollination success rates and, therefore, a higher yield of seeds.

The other methods mentioned do not directly enhance the seed set in self-pollinated plants to the same extent. Removal of pests might help improve overall plant health but does not directly relate to pollination processes. Increased water supply is essential for growth and development but does not address the pollination mechanism itself. Application of herbicides could harm beneficial organisms, including those that aid in pollination, or negatively affect plant health and development. Thus, the role of pollinator visits stands out in its direct impact on improving seed set in these plants.