Keep dishes washed, food in tight containers, garbage in tightly covered cans, dry pet food out of their reach, cracks caulked and gaps around pipes filled with steelwool. An upright, baited pint jar will trap cocroaches if the jar is placed where the roaches are likely to find it. A 2-inch wide band of petroleum jelly on the inside lip of the jar will prevent trapped roaches from escaping. Kill the insects by dropping them into hot water. Bait the jar with apples or potatoes.
Banana peels are most attractive to German cockroaches.
Change the bait frequently. If no roaches are trapped in 2 to 3 days, move the traps. Dusting the inside of the jar with talcum powder and using the same baits suggested above is also an effective trap as roaches will be unable to crawl out. Commercial traps are also available. When they clean themselves, they get the boric acid into their digestive system.