Since I’m new to StopPests in Housing, I’m taking some time to increase my understanding of pesticides. As I review terms, formulations, and cautionary statements, I thought I’d share what I learn with you as I go.
One of the goals of the StopPests in Housing Program is to use integrated pest management (IPM) to reduce the amount of pesticides used in housing. The reality is there will always be situations which call for pesticide use. We know choosing the right product to control a pest depends on many factors including the type of pest, location, cost, the level of infestation, and specific state pesticide or wildlife regulations. Because there is so much to it, we encourage you to leave pesticides in the hands of trained professionals. Whether you handle pest problems in-house or have a contract with a pest management company, knowing some basic terms can help you understand the best options for your site.
When selecting a pesticide, pay attention to the active ingredient more than the trade or brand name. The active ingredient is what actually kills the pest. The active ingredient is typically mixed in a formulation with inert ingredients (or carriers). This combination allows for handling, mixing, storing, and placing the product so that it reaches the pests. What follows is a brief description of formulations (or types) of chemical pest control products.
Baits rely on pests eating the product. Usually, only a small amount of the active ingredient is needed. That’s one of the reasons why baits are often promoted as the least toxic pesticide option. Baits come in liquid, gels, pastes, dusts, stations, pellets, and block forms. Baits usually target specific pests, but can be tasty to non-target species (like a pet dog). Some baits work slowly; this lets insects like ants (who share their food with their fellow ants) survive long enough to bring the poison home. Using baits too close to other pesticides or strong-scented cleaners may keep the target pest away—making the bait useless. Are your residents spraying after the pest management professional (PMP) visits? This well-intentioned effort may make the PMP’s efforts a waste of time. Therefore we discourage residents from using over-the-counter bug sprays. Many cockroach and ant problems can be managed with a little cleaning and some bait—not sprays. Take note—baits should only be used when a pest is present, otherwise you might be attracting unwanted visitors where there were none. Many baits go bad after about three months, but the label will let you know for sure. If a pest won’t be around to eat it, don’t put it out—you’ll be cleaning up the leftovers.
Granular pesticides have an active ingredient mixed with inert ingredients like clay to allow for easy spreading. The inert ingredient breaks down, releasing the active ingredient. Granular formulations are only used outside, around buildings. Rain dissolves the granules and allows the pesticide to be released. Granular formulations are not eaten as bait; they kill with direct contact and sometimes work as a deterrent. Two advantages that granular formulations have over liquid pesticides are; they release the active ingredient slowly, resulting in a longer residual effect and their weight allows them to drop and reach places sprays can’t, like under shrubs and other hard-to-reach places where pests live. Non-target animals, including children, should be considered before applying.
Dust formulations are often an active ingredient mixed with an inert powder (like talc) in a ready-to-use formula or entirely made of active ingredients like diatomaceous earth, boric acid, or silica products. “Active ingredient” doesn’t necessarily mean highly toxic, it’s simply the part of the pesticide that’s causing the insect to die—diatomaceous earth is one of the least-toxic pesticides there is. Dusts act by direct contact and are only effective when they remain dry. The most common problem we see with dusts is when people use too much. Read the label—if you can see the dust, you might have used more than you need. The pests should walk through the dust without realizing it – a big pile isn’t very subtle and pests will avoid it. Some dusts can be applied in hard to reach places like wall voids, attic soffits, and behind veneer—the voids and crevices where pests hide.
Aerosols kill pests by direct contact. When combined with a propellant, the active ingredient is evenly spread around. The finer the droplets, the longer they stay suspended in the air, which allows for greater distribution but increases the risk of people breathing in the pesticide. There’s also a concern about how far those droplets will travel before landing. The pesticide is bound to land on surfaces which people use – maybe even more than the target pests, increasing the risk of exposure for residents. Another concern with aerosols is the propellant is usually flammable. It’s ironic that aerosols are sometimes called “bug bombs,” because in fact they can be dangerous. Experts discourage the use of aerosols and TRAs (total release aerosols) not only because of the exposure risks but because they're often ineffective.
Fumigants are gaseous; in multifamily housing in most places in the US, they are typically only used as a last resort and only by professionals. The gas penetrates anywhere there’s air. The pest must breathe in the toxin. Fumigants are good for hard-to-reach spots like wall voids and hard-to-treat items like valuable antiques. Fumigants have some limitations: insect eggs are often unharmed, wet or treated wood have less penetration, and once the building is aired out, no pesticide is left behind. Depending on your point of view, no residual effect can be negative because there is no protection from future infestations or positive because residents are not exposed to residual chemicals. Use of fumigants often requires special training and licensing.
Liquid Sprays are diluted with water before application and come in a number of forms. Emulsifiable concentrates (EC), wettable powders (WP), microencapsulates (ME), or capsule suspensions (CS). For our purposes I won’t get into too much detail about each form. ECs are easily absorbed into skin. As with all pesticide applications, proper precautions and protective clothing should be used. Wettable powders and suspension concentrates are essentially powders mixed with water and require constant agitation. Microencapsulates are particles of active ingredient put inside a microscopic capsule. They can be designed for fast-acting or slow-release formulas.
With all these choices, it’s easy to see why we advocate leaving the decision about which product to use to trained professionals. Hopefully this guide will help you understand what your PMP is using and will help you discuss available pest control tools. All pesticides have some risk. The least risk treatment for any pest problem depends on a combination of toxicity of the pesticide ingredients and the risk of exposing people, property, and the environment to the pesticide. We didn’t even touch on all the non-chemical treatments like heat, vacuuming, and traps. We’ll save that topic for another blog post.
For further reading:
“Insecticide Basics for the Pest Management Professional” by Dan Suiter and Michael Scharf. Printable versions of the entire bulletin can be found here:
The National Pesticide Information Center: www.npic.orst.edu