The most important factor to consider when controlling Norway rats is population control. Killing individual rats is not enough; the idea is to control the entire population of rats in a given area, lest “new” rats move into treated areas as quickly as the “old” rats are exterminated.
Area-wide rat population control begins with taking actions to make an area less able to support a rat population, such as:
- Reducing the amount of food and water available by implementing proper sanitation and waste management procedures. This may involve outreach to businesses and residents in which the importance of proper sanitation to effective rodent control is emphasized.
- Reducing harborage by cleaning up refuse and debris in rat-infested areas.
- Utilizing non-chemical control methods such as exclusion to keep rats from entering buildings and other sensitive areas. The National Park Service has an excellent manual for rodent exclusion, which can be downloaded here. (Adobe Acrobat Reader required.)
- Continued monitoring to evaluate the ongoing effectiveness of the rodent control program.
Source: http://scarafaggio.us/ (free info about pest control and exterminating)