Poison Grain Bait Poison grain baits legal for prairie dog control in Colorado contain 2 percent zinc phosphide. Be careful with poison grain baits because bait placed outside burrows can kill non-target birds and mammals. For prairie dog control, zinc phosphide is registered for use only on rangelands. Product labels vary among manufacturers and with time. Carefully follow current label directions.
Zinc phosphide is a slow-acting toxicant that can be absorbed in small amounts through human skin.
Poison grain baits are classified as restricted use pesticides. Landowners must obtain private certification from the Environmental Protection Agency before they can purchase or use these products. Certification information is available from Colorado State University Cooperative Extension county offices. Poison grain baits are effective only when the prairie dog's most desirable food, green grass, has become dry and dormant. Fall baiting generally is most successful because prairie dogs eat grass seeds to build fat reserves for the winter.