What is the primary purpose of the milky spore application in soil?

The primary purpose of milky spore application in soil is to control pests, specifically targeting the larvae of Japanese beetles. Milky spore contains spores of the bacterium Bacillus popilliae, which infects and kills these pests when they consume it. By applying milky spore to the soil, it establishes a population that can persist for many years, effectively reducing the Japanese beetle larvae population over time. This biological pest control method helps maintain a healthier environment for plants by minimizing the damage caused by these pests, which can severely affect turf and ornamental plants.

In contrast, enhancing soil fertility, promoting plant growth, and preventing erosion are outcomes more associated with organic matter addition, fertilization, and ground cover, respectively, rather than with pest control.