Nov 12, 2012 – Roaches Are Agoraphobic


I am seeing roaches (normally Australian) climbing walls in the wide open. They are not near a bathroom or kitchen, but on a plain wall with no furniture even against it. My question is this: If we are limited now to crack and crevice treatments and cannot broadcast treat around the base boards how are we meant to treat for these roaches that seem to appear as if by magic. I don't even see them crawling along the floor to the wall. This is in my own house and I have only seen a couple, but a client doesn't want to see any. If you ask them where they see the roaches and they point to the wall, what good does it do us treating the kitchen and bathrooms? The baseboards are well sealed due to it being a new house.


I am a great fan of good magic, but even as I am stymied by the illusion performed right in front of my eyes I still recognize that it is not truly magic - it is an illusion. The roaches that just seem to appear crawling up these walls are in truth coming from some hidden place, probably below that wall, and this is what you need to determine. Where are the roaches actually hiding in this house? And, for Australian roaches that are great fans of high moisture, could there be an excessive moisture problem that is bringing them to that particular hiding place?

There are good reasons to avoid doing what we refer to as "baseboard treats", which has meant spraying a swath of insecticide along an exposed section of wall near the floor. The theory is that insects would then have to cross that treated surface and be killed by doing it. In fact, the amount of time a large roach actually spends on the treated surface is going to be very short, and the amount of active ingredient it is able to absorb in that short exposure will likely be far less than is needed to kill it. I remember many years ago when a lacquer-based chlorpyrifos formulation came out (Killmaster, for those who like to reminisce) and the manufacturer's rep described its use as "painting a barrier around openings that the roach has to cross". I pressed for an answer to the question "how long must the roach sit on a dry sprayed surface to absorb enough chlorpyrifos to kill it?", and the answer, somewhat begrudgingly, came back as 30 MINUTES! Well, no roach crossing a "barrier" was going to spend 30 minutes sitting on that narrow treated band. 

The better place to put the insecticide was directly into the crevices and gaps and holes and voids where the roaches spend most of the daylight hours. This dramatically increases the Contact Time with the active ingredient. So, in your case it is going to be necessary, for your own house as well as with customers, to spend awhile with a flashlight and knee pads figuring out a couple of things. One is how these large roaches are entering the structure from the outside, so that you can work on excluding them for the future. The second is to determine just where the roaches are spending the daylight hours when they are not visible. This is probably within wall voids, but if you rule that out then perhaps they have made their way along the floor-wall junction from somewhere else without being seen, and then make themselves known by crawling up a wall. 

These are big roaches and they can walk or run quickly and for long distances. Perhaps they are coming from the garage, perhaps from a bathroom where a pipe running through the wall has a large opening around it, perhaps from the laundry room or someplace else where they are able to find hiding places and a micro-habitat conducive to their needs of darkness, close quarters, and dampness. And, even though they are big roaches, they can still squeeze through some very narrow gaps, so there may be access points that are easily overlooked. Bottom line in my mind is that treating for roaches by placing the active ingredient onto exposed surfaces will have a far lower chance of killing the roaches than putting that material right into their harborage points. Doing so also greatly minimizes the chance that people or pets will contact that treated surface and will probably extend the residual life of the active ingredient. 

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