By Janet Hurley, Extension Program Specialist III
Rodent control is a multi-layer process and baiting for rats is just one part of the IPM process. However, using rodent baits is a question most School IPM Coordinators have concern over since they do work around children, food handling areas and non-target animal populations. The information below is some general information on rodenticides for use with the house mouse, roof rat, and Norway rats.
Pelletized bait should never be used around children or pets, even in a bait station as these pellets could be dropped in transit to the nest and could be picked up by human or pet.
So what’s the difference between a rodenticide and rodent bait? A rodenticide is a pesticide or other agent used to kill rats and other rodents or to prevent them from damaging food, crops, or forage. The term ‘rodent bait’ is something pest management technicians refer to as the product they place into the rodent bait stations. However for further clarification, this bait can be toxic (rodenticide) or non-toxic in which it is bait that tells the PMP if the rodents are in the area and should be fed toxic bait.
Both U.S. EPA and U.S. FDA both have regulations that require the use of tamper-resistant containers when using rodenticides around food handling areas, children, pets, and other non-target wildlife. Specifically EPA requires that rodent baits must be in block, paste, or pelleted forms and require use of tamper-resistant bait stations:
- If bait is to be placed in any indoor or outdoor location to which children under six years-of-age, pets or non-target wildlife have access.
- For all applications made outdoors and above ground. (citation)
- Baiting of burrows outdoors is permitted only for pelleted baits that are placed at least six inches down active rat burrows.
In 2008, EPA reviewed rodenticides and in 2010 they released changes that restricted the use of certain types of rodenticides for consumers (buy at the local store) and also how pest management professionals and agricultural operations can purchase and use these products as well. As such, there has been confusion over what products are still ‘legal’ and ‘how do I service this school account’.
Most everyone is familiar with warfarin. My mother takes Coumadin which is the human equivalent and they are both blood thinners. For rodenticides this class of product is referred to as the first generation of anticoagulants. They kill by preventing blood from clotting and it does take multiple feedings to gain success. The problem with this class of product is that when it was on the market for the public (consumer), children and animals could pick up the poison and ingest it, resulting in injury or death. Now the only way first generation anticoagulants can be used in the consumer market are ready-to-use bait stations that contain and/or are packaged with rodenticide bait that is in block or paste form. This means if you were to go to your local hardware store, you would find this product in one large container and there is no easy way for children or pets to tamper with it. For PMPs to use this product they must place inside tamper resistant container within 100 feet of buildings and other structure and must purchase the rodenticide in containers of 4 pounds or more.
Whereas the first generation anticoagulants take multiple feedings, the second generation of anticoagulants was created so that rodents who had become resistant to the first gen products would have an alternative permanent solution. Second generation anticoagulants are much faster acting; in some cases a single night feeding can result in death. However, this is dangerous when it comes to children and pets under the Risk Mitigation Decision. EPA took this class of rodenticide off the consumer market and these products can only be purchased for commercial pest control and structural pest control markets. Products containing second generation anticoagulants must be sold in containers holding at least 16 pounds of bait if they are labeled for use by professional applicators and at least 8 pounds of bait if labeled for use in or near agricultural structures. In TX, you must have a license with the TX Dept of Ag in the SPCS Pest category or 1D vertebrate pest control for agricultural pest control in order for you to use this category of rodenticides. These registered baits are for use by professional applicators to control rats and/or mice in or within 100 feet of buildings and other structures or for use in and near agricultural buildings and man-made agricultural structures. One item of note is that Vitamin K is considered to be an effective antidote to this type of rodenticide.
There are a couple of non-anticoagulants that require mentioning. Bromethalin is a single dose rodenticide that stops the cells in the nervous system from producing energy. You must be licensed to purchase this product. Cholecalciferol works at producing too much vitamin D; rats must eat several doses to kill them but this can be dangerous to humans and non-target animals if they are exposed as well. Zinc phosphide is an inorganic compound that combines phosphorus with zinc. When an animal eats the bait, the acid in the animal’s stomach turns the zinc phosphide into phosphine. Phosphine gas blocks cells from making energy which means the heart, brain, kidney and liver fail to work. Products with cholecalciferol and zinc phosphide are classified as restricted-use by U.S. EPA. Restricted-use products have the potential to cause unreasonable adverse effects to the environment and injury to applicators or bystanders without added restrictions. The “Restricted Use” classification restricts a product, or its uses, to use by a certified applicator or someone under the certified applicator’s direct supervision. Simply put these products are dangerous; in TX they are considered Red Category on school campuses and should be considered as a last resort.
This handy chart will help you begin to understand active ingredient and mode of action.
Understanding how rodenticides work is just as essential as bait station placement. Too often when I’m conducting IPM inspections I see some common mistakes made by all of us. The rest of this article is an effort to explain some of practices that should be adopted according to my lessons from Dr. Bobby Corrigan. First and foremost, exclude for all rodents. If they can’t gain access into the structure then the battle is half won. Even if they are inside, close up the building so you don’t leave them a one-way access point, however, they will hide and evade in order to survive.
Above image of House Mouse on a penny. Taken by Ed Freytag, City of New Orleans Mosquito, Termite & Rodent Control Board.
Mice (Mus musculus): typically with this species using snap traps, repeating/catchall traps, and other mechanical devices can capture the smallest to largest of populations. Mice are curious according to Dr. Corrigan, they will explore and if you use enough devices you can eradicate the population. But You the PMP must seal up areas, ensure that any clutter and food is cleaned up and make sure they don’t have any choice but go to these devices.
Roof Rats (Rattus rattus): at my house these are public enemy number one, this population of rodents thrive in suburban areas where there is a lot of vegetative cover. Since schools are often near residential neighborhoods, these rats can get into school buildings when the school or neighborhood undergoes construction, school administrators need to be aware of this so they can report activity immediately. These rodents can climb trees, chew through metal and dig under areas to survive; therefore exclusion is essential to keep these rats out of the building. Depending on the area rodent baiting can be done; however, where you place the stations and types of baits you use is important. Too often on my inspections I see the same type of rodenticide and bait stations placed in the same place as ‘routine’. In my experience you have to think like the roof rat and place those stations in areas where they ‘run’ and bait. For instance, the roof rats at my house seem to like the soft packs better than grains. And if it’s been dry, they will go to the liquid baits, which you set up in a specific feeding tube. These rodents will travel 500 feet or more; if you can set up stations 100 feet away from the building along a fence or block wall in a dumpster area, you can draw the rats away from the building. You will also want to think about using bait stations on roofs if that is where they are gaining access. In the meantime, seal up any holes in the structure.
Top: Norway Rat
Bottom: Roof Rat
Thanks to Ed Freytag for sharing this well captured image.
Norway rats (Rattus norvegicus): Bobby Corrigan refers to this species as the diabolical rat; this is the species that is seen in news stories from coast to coast. In cities, this is the rat most of us see in and around garbage. When I was working with the City of New Orleans Mosquito, Termite, & Rodent Control Board on their school IPM project, I saw what a large population of these rats can do. As with all rodent species exclusion and sanitation is tantamount. At the same time, experts really stress types of baits, bait station location and exclusion as the best way to reduce this population. In some of Dr. Corrigan’s research these rodents can travel far and wide, they range like wild animals, which mean that they may not come to the same location night after night. Again if you can bait within 100 feet of a building structure, check around vegetation areas, as these rodents love to burrow. These rodents do need water, so ask your pest control distributor about baits that could be used during drought conditions.
For more information about rodent control check out this IPM Action Plan http://articles.extension.org/pages/63911/ipm-action-plan-for-rodents
For more information about rodenticides check out the NPIC website http://npic.orst.edu/ingred/ptype/rodenticide.html
Handout on Rodenticides for use with trainings. [PDF]
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