Despite the worldwide ban, agricultural use continued in India, North Korea, and possibly elsewhere. As of 2013, an estimated 3,000 to 4,000 tons of DDT were produced for disease vector control, including 2786 tons in India. DDT is applied to the inside walls of homes to kill or repel mosquitoes. This intervention, called indoor residual spraying (IRS), greatly reduces environmental damage. It also reduces the incidence of DDT resistance. For comparison, treating of cotton during a typical U.S. growing season requires the same amount of chemical to treat roughly 1,700 homes.