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Rodent pest control: Use caution when using poison bait

By Gary Bogue
Wednesday, August 18th, 2010 at 7:09 am in Ground squirrels, Pest control, Pesticide, Pets & Poisons, Poison, Rat poison.

Ground squirrel. Photo by Brian Murphy, Walnut Creek, CA.
ground squirrel3

More problems with using poison to control rodents. There’s the risk of secondary poisoning of wildlife and pets as suggested in the DFG news release below. There is also the risk of direct poisoning of wildlife and pets around your house and yard when you use these poisons.

Rats and mice sometimes carry pieces of poison bait from supposedly safe bait stations used around your home and leave these pieces of poison bait lying in unprotected places in your yard or house where pets (or children!), or other wild creatures can find them.  If you must control rodents, I recommend using traps and NOT poisons. /Gary

DFG News, Aug. 17, 2010:
Wildlife Experts Issue Warning about Controlling Rodent Pests with Poison

State and county officials remind Californians to use caution when using poison baits (rodenticides) to control rodent pests. Careless use of these chemicals has injured and killed wildlife and pets throughout the state.

Rat. Photo by Flickr user asplosh used under a Creative Commons License.
rat asplosh

The California Department of Fish and Game (DFG) and County of El Dorado Environmental Management Vector Control have issued the warning in response to a recent increase in the use of such baits, as residents are responding to a rodent population explosion. In El Dorado County and other parts of the state, unusually high numbers of voles are creating problems for homeowners. Voles are small, outdoor rodents that build and use grass “tunnels.” They are similar in appearance to house mice, with short tails and smaller ears.

Residents should be aware of the dangers that some rodenticides pose to wildlife and pets, particularly through secondary poisoning. Secondary poisoning occurs when scavenging species eat dead or dying rodents that have been killed by rodenticides. Owls, hawks, other scavenging birds and predators such as raccoons, fox, skunk and coyote are at risk. Pets will also eat dead or dying rodents and unprotected bait. Deer may be attracted to the pellet forms of rodenticides.

Over-the-counter rodenticides – including many commonly known brands – that contain the active ingredients brodifacoum, bromadiolone or difethialone can only be legally used to control rats and house mice in and around structures. It is not legal to use these products in open areas such as pastures or fields.

Bait products that contain the ingredients chlorophacinone or diphacinone can be used legally to control outdoor rodent pests such as voles, ground squirrels and gophers. These compounds require multiple feedings to kill rodent pests, so they pose a lower secondary poisoning risk compared to rodenticides used to control mice and rats within homes, barns or other structures.

It is important to read rodenticide product labels carefully and to strictly follow all use directions. Rodenticides should only be used in small treatment areas close to structures. Be sure to check these areas daily for dead rodents. Collect the carcasses as soon as possible, place in plastic bags and dispose in garbage cans with tight lids that other animals can’t open. Always wear protective gloves when handling any dead animal.

Since 1994, DFG’s Pesticide Investigations Unit has confirmed at least
136 cases of wildlife poisoning from anticoagulant rodenticides. Brodifacoum was the poison most frequently detected. Animals impacted include coyote, gray fox, San Joaquin kit fox, raccoon, fox squirrel, bobcat, red fox, mountain lion, black bear, Hermann’s kangaroo rat, golden eagle, Canada goose, great-horned owl, barn owl, red-shouldered hawk, red-tailed hawk, Cooper’s hawk, turkey vulture and wild turkey.

“Since animals typically retreat to their dens, burrows or other hiding places in the final stages of anticoagulant poisoning, the number of non-target wildlife killed by this compound may be much greater than we know,” said DFG Environmental Scientist Stella McMillin. “For the research we did, most of the birds and mammals exposed to brodifacoum were collected in areas adjacent to urban development around the state.”

*** More information on protecting wildlife and pets from rodenticide baits is on the DFG website at

*** Protect your wild neighbors and pets from accidental poisoning. Use pesticides very carefully and follow all label directions, or choose organic or mechanical methods to control pests. More information on voles and alternatives to poison can be found on the University of California, Davis Integrated Pest Management Program website at

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3 Responses to “Rodent pest control: Use caution when using poison bait”

  1. Y.R. Craver Says:

    Hi Gary,

    My husband and I live in Martinez and we read your newspaper column every morning. I wanted to write to you when I found your website and your post urging caution with using rat bait. I learned the hard way this afternoon that rat bait stations are not pet-proof. Rats have been making a mess of my tomato plants in my backyard, so I put out a Tomcat Rat Bait Station. I put bricks on it, chicken wire around it, and cut up brush on top of it, to disguise the bait station and keep my little 18 pound 2 year old terrier-mix dog away from the bait. My dog is an in-door dog, so I thought that the rat bait station would be safe thus disguised in my backyard. I was wrong. I let me dog out into the backyard this after noon when she stood by the back door as usual to go out. After a little while (at most 30-minutes), I heard the sound of her throwing something plastic around the patio. I went out to discover that she had somehow retrieved the rat bait station, and she had dragged it down from our back slope onto our concrete patio and was tossing it around to dislodge pieces of blue rat bait. I didn’t see her actually eat the bait, but I assumed that she must have.

    It being Sunday, her regular vet was closed. I took her to the emergency vet in Concord. They gave her a shot and her vomit come out blue…thus confirming that had indeed consumed some of the blue rat bait. The vet later fed her activated charcoal to help to bind-up any residual poison in her stomach. Unfortunately, a blood test confirmed that she had already absorbed some of the poison, and it was affecting her blood, so the vet sent her home with a prescription of vitamin K. I was told to followup with her regular vet in two days and have her blood retested.

    Interestingly enough, the gentleman who arrived at the Concord emergency vet clinic right after me with his very large yellow lab had a similar problem. Due to rats in his backyard, he had distributed Tomcat Rat Bait in packets underneath his deck because he thought his dog would not be able to fit under the deck and reach the bait. He discovered that his dog had in fact eaten the bait because his dog’s feces was blue. The blood test that the emergency vet took confirmed that his dog had ingested and absorbed rat bait.

    I now do not know how to safely dispose of the bait station and the remaining unused bait. I also do not know what I can do to safely and humanely address the rat problem. We do not have any wood piles and our yard is very tidy…however, very large tomato plants. I have talked to my neighbors, and they are having similar problems with large brown outdoor rats. So, now that I know that rat bait is unsafe, I do not know what vermin control method to try. My terrier is only two years old, but this month she has caught and killed (but not eaten) two large brown rats in our backyard on two separate occasions in the morning when we let her out around. Given that she is an in-door dog, her hunting skills don’t seem enough to control what seems to be a rat population explosion this summer. Help!

  2. Caroline Says:

    A good alternative to poison is an effective mousetrap. There are ones made by Victor with a 100% kill rate. It kills and seals the mice inside, making it safe to use around kids and pets.

  3. Kristin Says:

    Help, we live surrounded by hundreds of acres of open space and have rates, LOTS of roof rats. I purchased bait stations and filled them up which seemed to work for awhile. But the raccoons seem to be able to remove the bait (as well as the station if not tied down). We attached cables to them and refilled them, but the raccoons shake them around and they are again empty. What can I use that raccoons cannot get in to! The rates are eating cables in the cars and house wiring!

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