As a class of compounds, borates --- inorganic compounds that contain boron and oxygen --- exhibit insecticidal properties. Homeowners and exterminators have used boric acid for cockroach control since the 1930s. If applied correctly, boric acid exhibits the longest residual effect of any insecticide. Boric acid has low toxicity for humans and other animals. Boric acid, however, has two drawbacks: it dissolves and washes away in water; and it does not kill cockroaches on contact. Cockroaches that crawl through boric acid later and ingest it as they preen themselves. As a result, boric acid takes about five days to work.
Purchase boric acid from a supermarket or hardware store. Most stores that carry boric acid stock it near other pesticides.
Remove any anti-tamper seals on the container. Leave the nozzle cap in place and shake the bottle vigorously for 10 seconds.
Remove the nozzle cap and squeeze the bottle to deliver quick "puffs" of powder to the area being treated. Apply only a very thin dusting to the treated surface. Cockroaches will simply avoid large clumps of powder. Treat any area where cockroach presence is confirmed or suspected, especially dark, inaccessible areas, such as under appliances and along baseboards.
Repeat the treatment after five days, if necessary.
Do not confuse boric acid and borax. Although borax also exhibits some insecticidal properties, boric acid and borax are chemically distinct compounds. If available, purchase boric acid in a plastic bottle with a small conical nozzle rather than in a bulk container.
Do not apply boric acid to any surface used for food preparation. Thoroughly wash any dishes or utensils that have possibly been contaminated.