Pest control is the regulation or management of a species defined as a pest such as any animal, plant, or fungus that impacts adversely on human activities or the environment. The human response depends on the importance of the damage done and will range from tolerance, through deterrence and management, to attempts to completely eradicate the pest. Pest control measures may be performed as part of an integrated pest management strategy. In agriculture, pests are kept at bay by mechanical, cultural, chemical, and biological means. Plowing and cultivating the soil before sowing mitigate the pest burden, and crop rotation helps to reduce the build-up of a certain pest species. Concern about the environment means limiting the use of pesticides in favor of other methods. This can be achieved by monitoring the crop, only applying pesticides when necessary, and by growing varieties and crops which are resistant to pests. Where possible, biological means are used, encouraging the natural enemies of the pests and introducing suitable predators or parasites. In homes and urban environments, the pests are the rodents, birds, insects, and other organisms that share the habitat with humans, and that feed on and/or spoil possessions. Control of these pests is attempted through exclusion or quarantine, repulsion, physical removal, or chemical means. Alternatively, various methods of biological control can be used including sterilization programs. The history of pest control dates back to ancient times and has been used in agriculture since then. The conventional approach was probably the first to be employed since it is comparatively easy to destroy weeds by burning them or plowing them under and killing larger competing herbivores. Techniques such as crop rotation, companion planting, and the selective breeding of pest-resistant cultivars have a long history. Chemical pesticides were first used around 2500 BC when the Sumerians used sulfur compounds as insecticides. Modern pest control was stimulated by the spread across the United States of the Colorado potato beetle. After much discussion, arsenical compounds were used to control the beetle and the predicted poisoning of the human population did not occur. This led the way to a widespread acceptance of insecticides across the continent. With the industrialization and mechanization of agriculture in the 18th and 19th centuries, and the introduction of the insecticides pyrethrum and derris, chemical pest control became widespread.