Biological control of aquatic weeds commonly uses which agent?

• A. Use of herbivorous fish
• B. Deep plowing of sediments
• C. Application of broad-spectrum pesticides
• D. Heating water to kill roots

Answer: (A)

Biological control relies on using living organisms to reduce pest populations. In aquatic weed management, herbivorous fish are commonly used because they eat the weeds, helping to keep their growth in check over time. Grass carp, often used in waterways, graze on a variety of aquatic plants and can provide ongoing weed suppression with less chemical input. This approach is typically more sustainable and targets the weeds with fewer impacts on non-target organisms than chemical or physical methods. The other options are not biological controls: deep plowing is a mechanical disruption of sediments, broad-spectrum pesticides attack many species and can harm ecosystems, and heating water is a physical method that kills roots without employing a living control agent.