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Through most of the last century, the German cockroach was considered the most difficult-to-control pest in buildings. Once effective cockroach baits were finally developed, control of this troublesome pest became easier. Over-reliance on gel baits as the primary control tool, however, has led to a return to a more difficult-to-control cockroach.

Individuals within German cockroach populations simply avoid certain baits, which allows the infestation to continue. Also, baits may not be placed near many active harborages, which allows populations to survive. For these reasons, a discussion of techniques and strategies other than baits for controlling German cockroaches may prove beneficial to many pest professionals.

 

The Basics

The most effective strategy for German cockroach control involves implementing multiple control techniques. One thing the German cockroach has shown us over the decades is its innate ability to adapt, survive and thrive. Reliance on only a single type of insecticide often produces cockroach populations that have physiological or behavioral resistance to that particular insecticide.

Employing several different insecticides, formulations and nonchemical strategies negates a German cockroach population’s ability to develop resistance to any single technique or insecticide.

Experience has shown that if one fails to achieve at least 98 percent reduction in German cockroach numbers within the first four to six weeks of an initial service, the infestation typically continues. Killing 950 out of 1,000 cockroaches sounds like a good job, but 50 roaches left behind will continue the infestation. As industry consultant Dr. Austin Frishman says, “It’s not how many you kill that’s important, it’s how many you leave.”

VACUUMING. One of the most important techniques for initial services where more than a few cockroaches are present is vacuuming (Figure 1). A vacuum device provides instant population reduction and should be used to remove cockroaches directly from surfaces and those flushed from cracks and voids. It is possible to achieve 50 percent+ immediate control of an infestation by vacuuming alone. An added benefit is the customer will see far fewer dead and live cockroaches in the days following the initial service. Any pest professional who currently does not use one should strongly consider purchasing a good HEPA vacuum device.

TREATMENT TECHNIQUES. The choice of which product formulation to use in treating a particular site depends on the site where cockroaches are harboring. German cockroaches spend the majority (75 percent+) of their time resting within cracks and voids. Cockroaches spend very little time on exposed surfaces unless the surface is somewhat protected, such as the back corner inside a cabinet, the wall behind a sink splash guard in a restaurant, or the back of a piece of furniture close to a wall. Therefore, a pest professional who is using crack and crevice (C&C) and void treatments most of the time will have greater success against German cockroaches. Professionals who primarily only use a compressed air sprayer applying spot treatments are more likely to have problems in eliminating cockroaches.

FORMULATIONS. For cockroach control, it is more effective to use insecticide formulations designed for application into cracks and voids. The best non-bait choices for cracks and void treatments are dusts and aerosols due to their ability to penetrate and distribute throughout a crack or void, then contacting and killing any cockroaches that may be hiding there.

Water-based formulations (EC, SC, CS, WP) are typically labeled for crack and crevice (C&C) application and can be applied to cracks using a C&C tip on the sprayer. The issue with water-based products in cracks is potential for poor distribution to surfaces inside a crack, and the fact that with vertical cracks, the application can run out onto non-target surfaces. Water-based formulations are also not the best choice for voids due to distribution concerns. Suitably labeled water-based formulations can, however, be effectively applied to cracks and voids using an aerosol-generating machine (e.g., Actisol, Patriot).

 

Importance of Detection

Successful elimination of a German cockroach depends on finding and treating every active harborage. In doing so, one must treat all suspected/likely harborages, with many such harborages being simply flushed with pyrethrins and checking for activity. A single missed active harborage with numerous cockroaches can allow an infestation to persist. It’s been my experience that overlooking some harborage(s) is the single biggest reason for callbacks.

FOCUS ON LIKELY AREAS. A key example occurred in the waiter station of a country club restaurant. The pest professional responsible for servicing the country club was having repeat complaints about cockroaches in the waiter station. When I became involved, I do what I always do, I look for the sites where German cockroaches are most likely to occur — places with moisture and warmth. In this case, my eyes were drawn immediately to a cooler used to store wine. Looking behind the cooler, I found a towel in which four cockroaches were hiding. Pulling off the front grill revealed dozens of cockroaches hiding in and around debris, including a manila file folder (Figure 2). Vacuuming all accessible cockroaches and removal of the folder and all debris was followed by a few C&C treatments in available cracks and spot treatments to exposed surfaces where cockroach fecal spotting was evident.

Figure 2. Pulling off the front grill of the cooler revealed dozens of cockroaches hiding in and around debris, including a manila file folder.
Stoy Hedges

WHAT’S NOT THERE. Another tip when cockroach complaints persist in a given room or apartment is to look at items that are present in the site when the customer sees cockroaches but are not there when service is done. In one case, cockroaches in an apartment were traced to a stack of dishes that were removed from a cabinet in preparation for the service.

Another case involved a banquet hall in a country club where people saw cockroaches on the food tables during every reception, banquet or event in the room. When the pest professional checked the area, he could never find evidence of activity, but he treated the cracks in the tables, behind baseboards and trim, and inside wall voids along the wall where the food tables were located. When the problem continued, I became involved and the first question I asked the facility manager was, “How are these tables decorated during an event?” When the room was empty, the tables were bare, but the manager said they would put on skirts and tablecloths, then put down large mirrors on which food trays would be placed. I asked to see the mirrors (which were stored in the kitchen under a table). Flipping the mirrors over, I discovered each was infested by 20 or more cockroaches hiding in the crack between the outer edge and the wooden backing forming the mirror. The insects were removed by vacuuming and the facility had the cracks filled with sealant. Every event, the cockroaches were carried out to the tables and then food was brought to them. How much better could it be for cockroaches?

QUESTION THE CUSTOMER. The people working or living in the building are there all the time and are the best source of information where cockroaches are living. German cockroaches seldom travel more than 10-12 feet from their harborage to look for food or water so an active harborage will be very close to where cockroaches are seen by the customer or employees. In commercial facilities, ask employees to show you where they last saw a cockroach. Typically, this is the area where most of the activity is occurring so look for sites where cockroaches would prefer to hide nearby.

In one case in a restaurant, a dishwasher showed me a table where he saw cockroaches. At this table was a metal knife rack attached to the wall. When I looked underneath, I could see cockroaches inside. I removed it from the wall and vacuumed dozens of insects from inside. A similar case with cockroaches pointed out by a cook was quickly traced to the inside of a can opener on a prep table.

DIFFICULT TO SEE. Many pest professionals tend to look at and treat the easiest-to-see and -reach harborages. For example, when checking a stainless steel table or stove in a restaurant kitchen, it is easy to see the back corners and edges, both under the table top and under the bottom shelf near the floor. Treating only the rear, easy-to-see harborages leads cockroaches to move to the front edges of the equipment and legs where it may be impossible to stick one’s head to see. For this reason, a very important tool is an inspection mirror, which allows inspection of all parts of a table, oven, etc. Continued infestations commonly involve this issue.

 

Figure 1. One of the most effective tools for an initial cockroach service is a vacuum.
Stoy Hedges

Common Overlooked Sites

In my 40 years in pest control, I have found three areas that typically are overlooked for treatment but which serve as sources for continued infestations. These areas can be a pain to treat which is why they don’t get treated as often as they should.

WALL VOIDS. By far the most important of these is wall voids, particularly in food handling/preparation areas. I have had numerous cases where simply treating the wall voids solved a chronic infestation. In commercial kitchens, the wall voids of greatest importance are those behind sinks, behind the dishwasher unit, and behind the cooking line (stoves and ovens). When drilling walls, a chalk line can be snapped to ensure the drill holes are level on the wall or locate the drill holes (where possible) underneath tables, sinks, etc. where they are out of sight. Space the holes at 16-inch intervals and install plastic wall tubes, if available, into the holes to permit future reapplications as needed.

Wall voids in homes and apartments seldom require retreatment except for where pipes penetrate walls. In my experience where severe German cockroach infestations exist in homes or apartments, drilling and treating wall voids through the backs of the kitchen cabinets and bathroom vanities has helped to alleviate persistent infestations.

Residual dust products are the best choice for treatment of wall voids due to their excellent dispersal within voids and their long residual life. Wall voids in high humidity areas (dishwashing areas) will require more frequent retreatment than drier voids. Residual aerosols labeled for wall voids may also be used as well as water-based or oil-based formulations labeled for application using an aerosol-generating machine.

ELECTRICAL CONDUIT BOXES. Electric wires in commercial kitchens will be housed inside conduits that lead to outlet boxes and junction boxes. These are typically located at floor level and on walls. German cockroaches love to live inside these boxes and travel inside the conduits from area to area. It takes time to unscrew the plates on junction boxes to check for cockroaches. Flush (don’t used water-based aerosols) and vacuum any insects found inside, then apply a light amount of residual dust into the conduits leading into the box and then into the box itself before the plate is re-secured to the box.

FALSE CEILINGS. It is not often that German cockroaches will be found in false ceilings but when they are, usually the population has been high at some point or poor control practices (e.g., space treatments) have been employed.

False ceilings should at least be inspected for activity during the initial service, focusing on ceilings above the stove line, the dishwashing area and bar areas in the dining room. Look for live and dead cockroaches and fecal spotting. Should cockroaches be found, remove them by vacuum and apply C&C and spot treatments where activity is noted. Recheck ceilings with activity, but if none is found, checking the ceilings may be done only as needed and if an infestation persists.

 

Summary

Elimination of German cockroaches requires diligence and effort. If one puts the initial effort into the cleanout to achieve that goal of 98 percent+ control that first month, the population can be brought to zero with continued vigilance. Applying the same one or two products every service for extended periods can lead to chronic infestations and possibly development of insecticide resistance.

For the longest-lasting and most consistent results, employ several different formulation types or insecticides combined with vacuuming. Customer cooperation with sanitation is also key. Use products designed for treating cracks and voids and limit spot treatments to sites where cockroaches are known or suspected of resting on exposed surfaces. Target inspections where you think cockroaches are most likely to harbor in a given area — sites with moisture, warmth and natural surfaces like wood and cardboard. When an infestation persists, you’ve missed one or more active harborages — find those and the problem can be resolved.

Editor’s note: This article originally appeared in the Spring 2020 edition of PCT Canada. Learn more about the publication.