Gel bait usually fails for one of two reasons: too much of it, or the wrong two inches. A 30 g tube placed as pea-sized dabs along the cracks roaches already use will collapse a German cockroach colony in about three weeks. Squeezed into one long bead behind the baseboard, the same tube does very little.
What the gel is doing
This one is fipronil 0.05%, a slow-acting stomach poison carried in a food gel. A roach eats a dab, walks back into the void it came from, and dies there a few days later. Before it does, the others in that void eat what it carried — the gel in its gut, its droppings, its body — and take a dose of their own.
That chain is the treatment. The dabs are only the delivery.
Slow is deliberate. An insecticide that kills in minutes drops roaches in the open, where nothing eats them, and the rest of the colony avoids the area. Three to five days is long enough for the sharing to happen.
Where the dabs go
German cockroaches stay within a few feet of warmth, water and a gap the thickness of a coin. Bait goes into those gaps, at the edge of the dark, never out in the open.
- Cabinet doors. On the hinge plate, and in the inside corner of the frame beside it.
- Under the sink. Along the lip of the cabinet floor, and where the pipes pass through.
- Behind the refrigerator. On the frame near the compressor, not on the warm coils.
- Dishwasher. Down both side edges of the panel, and under the front lip.
- Drawers. On the track and in the back corner — the drawer nearest the stove first.
- Bathroom. Vanity hinges, the seam behind the toilet tank, the corner under the sink.
Space the spots 12 to 16 inches apart along each run of crack. One 30 g tube covers up to 60 linear feet of cracks and crevices, which is an ordinary apartment kitchen, one bathroom, and the cabinets between them.
How big is a dab
Pea-sized, about an eighth of an inch across. If a dab looks like a small coin it is too big: the surface dries before the gel underneath is finished, and a dried dab stops being food. A single tube should give you somewhere between 150 and 200 spots.
Roaches feed in small amounts. Four small dabs along one hinge do more than one heavy line, because four points get found by four different insects.
The tube in these photos is our 30 g roach gel bait syringe: fipronil 0.05%, up to 60 linear feet of cracks.
Four rules that decide the result
- Bait in the evening. They come out after dark, and fresh gel is at its most attractive in the first few hours.
- Never spray over it. A repellent spray or a fogger in the same cabinet makes the area unattractive and the gel stops being eaten.
- No harsh cleaner on the spots. Wipe with soap and water before applying. Bleach or degreaser residue on the surface puts them off the gel.
- Keep it away from food. No dabs on counters, cutting boards, utensils, or anywhere a plate gets set down. Cracks and voids only.
What the next three weeks look like
Days 1 to 3. Little visible change, sometimes a bit more activity. Both are normal — the insects are finding the gel and carrying it back.
Week 1 to 2. Dead roaches near the nest, and fewer crossing the floor at night. Nymphs are still out; they hatch on their own schedule.
Week 2 to 3. Mostly small nymphs, then a sharp drop in everything. That is the colony running out of replacements, not a second wave.
Week 4. Check the spots. Empty dabs mean the area is still active and should be refilled. Dabs that are still full after two weeks are in the wrong place — move them closer to the void.
When to re-bait, and when to switch
Refill any spot that has been eaten. Leave untouched gel alone: it stays palatable for weeks, even when it looks dry and dusty.
If gel is being ignored in spots that used to work, stop adding more of the same. Rotate to a different active ingredient — imidacloprid, indoxacarb or dinotefuran — for the next round. Roaches develop bait shyness the same way they develop resistance to sprays.
Safety, in plain terms
- Read the label and follow it. On a pesticide, the label is the instruction that counts.
- Wear gloves if you have them, and wash your hands afterwards.
- Put every dab where a child or a pet cannot reach it, then close the cabinet.
- Cap the syringe between uses and store it at room temperature, out of sunlight.
- If it gets in the eyes or is swallowed, call Poison Control on 1‑800‑222‑1222 and have the label to hand.
When one tube is not enough
Bait kills roaches; it does not fix a leaking pipe, an open bag of pet food, or cardboard boxes stacked against a warm wall. If you see nymphs in daylight, or roaches in more than one room after three weeks of baiting, the infestation has outgrown a single tube: add an insect growth regulator, seal the gaps, and treat the whole unit at the same time.
For the biology behind all of this — why one sighting is never one roach — read German cockroaches: one sighting means a colony. For the places they hide, see where roaches spend the 90% you never see.