[Vertebrate Pests] Exterior Norway rat control, part II

In last month’s column, I discussed the techniques for baiting exterior rodent burrows. This month, let’s examine the use of tracking powders, which is perhaps the second most commonly used method for treating Norway rat burrows.

TRACKING POWDERS. Rodenticide tracking powders contain a toxic active ingredient blended into a powder carrier (e.g., clay). Occasionally, tracking powders are incorrectly referred to as "dusts." But the term dust should be avoided because a pesticidal "dust" is different than a "powder." The tracking powders used for rat control contain either one of the anticoagulant toxicants diphacinone or chlorophacinone.

Tracking powders applied to a rat’s burrow are designed to be picked up on the rodent’s foot pads, fur and/or tail during their travels. The primary route of the powder’s toxicant is via ingestion when the rodent licks its body during grooming. Technically, small amounts of the powder also may absorbed through the rodent’s body or via inhalation.

Generally, only a small amount of powder is picked up by a rat after passing through a tracking patch. To compensate for this, the concentrations of the toxicant in tracking powders are much greater than those used in baits containing the same active ingredient. For example, a diphacinone tracking powder is formulated to a 0.2% concentration. This concentration is 40 times stronger than the diphacinone mixed into baits (0.005%). This increase in concentration, however, does not necessarily mean a rodent will die more rapidly than if it consumed an anticoagulant food bait. Similar to anticoagulant baits, it usually requires three to 10 days for a rat poisoned with tracking powders to die.

IMPORTANT CONSIDERATIONS. Because all rodenticide tracking powders are restricted use pesticides, safety is paramount in their use. Thus, the following are some on-the-job considerations for the correct and safe use of tracking powders.

• Generally, tracking powders should be considered a specialized approach to be used only when baits and/or traps fail due to finicky rodents that are either trap shy, or are uninterested in baits because of an abundance of food alternatives.

• Prior to using any tracking powder, re-read the label to ensure the site being considering is allowed by law and to follow all safety and personal protection guidelines. When applying tracking powders, always wear gloves. Also wearing a MSHA/NIOSH approved dust/mist (N95) respirator is recommended.

• It is important to note that exterior use of tracking powders is restricted to: "only rat burrows that are located along the periphery of buildings and that are likely to serve as routes of entry into these structures." A typical situation where tracking powders might be used would be an abandoned lot next to an abandoned building where perhaps food trash is a constant battle and the rats are not responding to baits.

• Tracking powders should never be applied in areas (e.g., community parks) where rats may be traveling along the same paths or are active on the same surfaces that people, pets or wildlife might travel. Rats might carry the powder on their feet or body to these areas when leaving a treated burrow.

• When treating burrows next to building foundations, check to ensure air intake ventilators, duct openings or exhaust fans are not nearby. In these situations powders could be sucked into the building or blown about into the air where people could be exposed.

• When just a few burrows need to be treated a hand-held bulb duster can be used.

• A typical diphacinone label dictates that each burrow should receive about 5 grams of powder (i.e., approximately one-sixth of 1 ounce). Tip: One ounce of tracking powder is about 6 level teaspoons of powder.

• Tracking powders should not be applied into burrows on rainy days, or before heavy rain is expected.

• Flags should be used to mark treated areas. One flag can be used for a general area (i.e., a flag is not needed for each burrow system).

• The location, day, time and the amount of materials applied to the burrows should always be clearly recorded in service records.

• A week or so after treatment, burrows can be caved in with dirt, leaves or wads of paper. These closed burrows are then re-inspected within the next couple of days (e.g., one to three days). Re-opened burrows (i.e., still active) can be scheduled for re-treatment as per label directions. Once control is achieved, all burrows should be filled in.

DIFFERING OPINIONS. The use of tracking powders for exterior rat control is not without controversy. For example, some argue that once a toxic powder is applied to an exterior rodent burrow, the disposition of that pesticide is now uncertain. Rats exiting a treated rat burrow will technically be carrying and possibly depositing a pesticide residue to wherever they travel upon leaving the burrow. To this point, some question the logic of the label that stipulates application of the powder into only those burrows that serve as a "likely entries" into structures.

In other words, if rats enter buildings from such burrows that have been treated with a tracking powder, are they not likely to transport the powders, albeit small amounts, into the building?

In most cases, such areas are likely to be crawl spaces, basements and perhaps other areas not heavily visited by people. Nevertheless, with all the attention these days on indoor air quality, sick building syndrome, molds, allergens, lead and so forth, introducing a pesticidal powder into a structure even in very small amounts should be carefully thought out indeed. Tracking powder labels clearly state: "keep away from humans, domestic animals or pets."

Conversely, others contend that the amounts that might be carried on the feet or fur of a rat exiting a treated rat burrow are so small so as to be of little toxicological consequence. Maybe. But each case is different. Too, our industry has learned how difficult it is to explain that small amounts of pesticides around people and pets are of "no threat."

Litigation has resulted over lazy applicators simply "blowing" tracking powders into burrows without any regard for applying the correct label dosages, resulting in significant amounts of powder being transported out of the burrows and onto the ground exposing people and non target mammals (cats, dogs, squirrels, birds, etc.).

It shouldn’t come as any surprise to any pest management professional that the most effective treatment for Norway rat infestations is to identify and eliminate the food source and harborage. But unfortunately in the "real-world," this is not always practical or even possible. Thus, treating exterior burrows (by either baiting or use some other control approach), is occasionally a necessary aspect of Norway rat control.

Personally, when I’m anticipating the need to supplement sanitation efforts with burrow treatments, I almost always lean in the direction of direct burrow baiting efforts or installing tamper-resistant bait stations containing secured baits or rat traps.

I believe tracking powders should be considered a highly specialized approach to be used only when baiting or trapping programs have failed to control the last remaining rats. And above all else, safety is priority one.

The author is president of RMC Pest Management Consulting and can be reached at rcorrigan@giemedia.com or 765/939-2829.