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Zinc phosphide bait, like its fumigant cousin, kills prairie dogs with the use of phosphine. Once the zinc phosphide bait is consumed, it reacts with moisture in the gastric juices to liberate phosphine gas. The prairie dog inhales the gas and dies by suffocation.
Application consists of two visits: an application of pre-bait and the application of the bait. During the pre-bait, plain oats are applied to entice and train the prairie dogs to pick up the bait. The bait is applied after the prairie dogs show that they have accepted the pre-bait. The pre-bait and bait are to be applied at the rate of 1 teaspoon per active mound and isto be scattered on or near the mound.
For Black-tailed prairie dogs, zinc phosphide application can take place from July through February. For White-tailed prairie dogs, due to their hibernation, some zinc phosphide labels allow it to be applied in the spring.
Zinc phosphide poses a very slight risk of secondary poisoning, although the carcass of a prairie dog is not generally toxic enough to cause any harm to a larger animal that may feed upon it. It does, however, pose a threat to non-target species that have access to the bait itself. All livestock and pets should be kept from the area for at least a couple of weeks and great care should be taken to avoid any location where waterfowl may access the bait. Frost, dew, rain, and sunlight will eventually degrade any unconsumed bait.
There are two types of voles in our region, meadow voles and prairie voles.
Best known for the damage they cause to the base and roots of small trees and shrubs and the trails they leave in lawns, voles do their greatest damage underneath the cover of snow, when they can forage all day and night, safe from the constant threat of predators.
Where possible, we prefer to use zinc phosphide baits for the treatment of voles as the bait is both very effective and tends to be a bit safer for pets and other wildlife. However, the use of zinc phosphide is banned for residential use. It can be used on non-residential lawns as well a number of other locations including some crop land, rangeland, groves, vineyards and golf courses.
For residential use, vole control is limited to anti-coagulant baits, traps, habitat modification, exclusion and repellants. Unfortunately, all but the baits are impractical for larger areas of infestation.
Having outdoor cats in the area can help in the control effort. However, voles are known for their prolific breeding. With a very high mortality rate, they need to out-breed their predators. Voles will have 1 to 5 litters per year on average, but can have 10 or more litters, and in a year. Their young reach maturity in a little over a month and will have their own litters.
Voles can be treated with either zinc phosphide or anti-coagulant baits any time of the year if the infestation requires it. However, the best time to treat voles is in the fall, before we might get any lasting snow cover.
Control efforts and cost will vary according to the property and the extent of the problem.For cropland, orchards, golf courses and larger lots where we can use zinc phosphide, we charge by the acre.
Carbon monoxide causes death by tying up the oxygen transport in the body, leading to asphyxiation. There are two options for administering carbon monoxide: gas cartridges and exhaust gases.
With gas cartridges, sodium nitrate and charcoal are ignited and produce a large, but short-lived, cloud of carbon monoxide and carbon dioxide smoke inside the burrow. The cloud of gas from a gas cartridge lasts for only an hour or two inside the burrow. The cloud of carbon monoxide has an odor and is visible, making it safer than phosphine when working around occupied buildings. In the slight chance that the gas gets inside a building, it will be detectable and the building should be evacuated and vented. Due to its extra safety, we must use gas cartridges on any burrows within 100 feet of any occupied, or potentially occupied, structure.
Gas cartridges are very safe for people, pets, livestock, and other wildlife but have a lower effectiveness rate than aluminum phosphide. Gas cartridges are also more expensive to purchase and apply.
Carbon monoxide can also be applied with the use of a PERC® (pressurized exhaust rodent controller) or similar machine. Carbon monoxide is generated by a gasoline engine, cooled and stored in a tank before being introduced to the burrows by hose. The burrows are sealed in the process. As the carbon monoxide from a PERC machine has no color or odor, the State of Colorado requires that this method not be used within 100 feet of an occupied structure.
The PERC machine needs12 to 15 minutes to treat each burrow so that a single machine can treat 200 to 240 burrows in an eight hour work day. This is much slower than with aluminum phosphide and so the cost per burrow is higher.
Many cities and towns are using carbon monoxide exclusively for prairie dogs on their own lands and recommending or requiring its use on some private land within city limits. More cities are likely to join them in coming years.
Carbon monoxide is seen by some to be more humane than phosphine gas. The public may also be more comfortable with something they know (carbon monoxide) over something they are unfamiliar with (phosphine).
Aluminum phosphide is both very effective for removing prairie dogs and safe for people, pets or livestock in the treatment area. When compared to other pesticides, aluminum phosphide is safer in the larger environment with little to no risk to anything outside of the sealed burrows.
Aluminum phosphide tablets are dispensed down into each active prairie dog burrow before the burrows are sealed with paper and soil. The Aluminum phosphide reacts with moisture in the ground or atmosphere to liberate phosphine gas. Phosphine is a colorless and odorless gas, which, once inhaled, causes a metabolic crisis in the body and death typically follows soon after exposure.
Though phosphine is slightly heavier than air, we do seal the treated burrows to keep the gas underground and to help prevent prairie dogs from escaping. Given the time-release aspect of the fumigant tablets, the phosphine gas may remain in the burrow for up to ten days, though 3 to 4 days is more likely.
For safety, aluminum phosphide is not to be used within 100 feet of any occupied structures, nor within 25 feet of other non-occupied structures, i.e., tool sheds, storage sheds, loafing barns, etc. As phosphine is colorless and odorless, it could seep into a building through a hole or crack in the foundation. The one-hundred foot buffer zone is intended to mitigate that risk.
Rozol ®(chlorophacinone) and Kaput-D® (diphacinone) are anti-coagulant baits for Black-tailed prairie dog removal. Both agents thin the blood and cause death by blood loss and/or dehydration.
Each dose of bait must be placed 6” down inside each active burrow. The prairie dogs begin to die off 4 to 5 days after consuming a lethal dose of the bait. According to the label, the site must be visited by the applicator starting four days after application is made and then every two days for 14 to 21 days to dispose of any carcasses and clean up any bait that may be out onto the surface.
Anti-coagulant baits do pose a risk of secondary toxicity. Birds or animals thatfeed upon the carcass of a poisoned prairie dog may be exposed to enough poison to be dangerous. Grain eating animals are also at risk of poisoning by the bait itself, as are fish, if the bait is applied to surface water. As such, no livestock should be on the site for a month or more after application. Absolutely no broadcasting of either bait is allowed for prairie dogs. If pets are exposed to the bait, there is an antidote (potassium).
The effectiveness both anti-coagulant baits can vary greatly depending on the condition of the available vegetation and the health of the prairie dog colony. In our area, Rozol® and Kaput-D® baits can only be applied between October 1st and March 15th.
Both anti-coagulant baits are only for Black-tailed prairie dogs and are limited to rangeland and adjacent non-crop areas, making them unavailable for most urban and suburban settings as well as farmland and orchards.
Both baits have proven to be very effective at removing prairie dogs and at about half the cost of fumigation. For larger colonies and in certain soil profiles (very rocky or porous soils), bait may be your best option for the initial control.
The EPA allows the use of both aluminum phosphide and carbon monoxide (gas cartridges or PERC machine) for the fumigation of prairie dogs. We recommend using aluminum phosphide in most locations, although gas cartridges are necessary in some. We will apply gas cartridges to all burrows if the customer desires.
ALUMINUM PHOSPHIDE. Aluminum phosphide is both very effective for removing prairie dogs and fairly safe for people, pets, or livestock in the area. When compared to other pesticides, aluminum phosphide is safer in the larger environment with very little to no risk to anything outside of the sealed prairie dog burrows.
Aluminum phosphide tablets are dispensed into each prairie dog burrow. The Aluminum phosphide reacts with moisture in the ground or atmosphere to liberate phosphine gas. Phosphine is a colorless and odorless gas, which, once inhaled, creates symptoms similar to carbon monoxide. The affected animal dies by suffocation.
Though phosphine is slightly heavier than air, we do seal the treated burrows to keep the gas underground and to help prevent prairie dogs from escaping. Given the time-release aspect of the fumigant tablets, the phosphine gas may remain in the burrow for up to ten days, though 3 to 4 days is more likely.
Carbon monoxide causes death by tying up the oxygen transport in the body, leading to asphyxiation. There are two options for administering carbon monoxide.
With gas cartridges, sodium nitrate and charcoal are ignited and produce a large, but short-lived, cloud of carbon monoxide and carbon dioxide smoke inside the burrow. The cloud of carbon monoxide has an odor and is visible, making it safer than phosphine when working around occupied buildings. In the slight chance that the gas gets inside a building, it will be detectable and the building should be evacuated and vented. Due to its extra safety, we must use gas cartridges on any burrows within 100 feet of any occupied, or potentially occupied, structure.
The cloud of gas from a gas cartridge lasts for only an hour or two at best in the burrow. Gas cartridges are very safe for people, pets, livestock, and other wildlife but have a lower effectiveness rate than aluminum phosphide. Gas cartridges are more expensive to purchase and apply.
Carbon monoxide can also be applied with the use of a PERC® (pressurized exhaust rodent controller) machine. Carbon monoxide is generated by a gasoline engine, cooled and stored in a tank before being introduced to the burrows by hose and wand. The burrows are sealed in the process. As the carbon monoxide from a PERC machine has no color or odor, the State of Colorado recommends that this method not be used within 150 feet of an occupied structure. We do not currently use a PERC machine but may in the future.