What is the function of residual herbicides?

Residual herbicides are designed specifically to provide prolonged control of weeds through applications that remain active in the soil over an extended period. These herbicides can inhibit the growth of germinating weed seeds or newly emerged weeds even after the initial application. This long-lasting action is beneficial for maintaining weed control throughout a crop's growing season, reducing the need for multiple treatments and helping to manage weed populations effectively.

The other options focus on different aspects of weed management and plant growth. Immediate control of visible weeds is typically achieved with contact herbicides or quick-acting formulations, rather than residual types. Enhancing the growth of desirable plants pertains more to fertilizers or growth regulators, not herbicides, which are primarily designed to suppress unwanted vegetation. Detering pests is a function related to insecticides or repellents, which serve a different purpose in pest management as they target harmful insects rather than focusing on weed control.