Explain the biological control of weeds with the help of two examples.

Biological control of weeds include growing smoother crops which do not allow weeds to grow nearby e.g., Barley, Rye, Sorghum, Millet, Sunflower etc. They eliminate weeds through chemicals. Crop rotation with these crops reduces the incidence of weeds.
Another way of weed control is the introduction of specific insects which feed on the weeds. e.g., Extensive growth of Opuntia in India and Australia has been checked by introduction of its natural herbivore-Cochineal insect (Cactoblastis cactorum). Similarly growth of Klamath weeds Hypericum was checked by USA through introduction of Chrysolina beetles.