Apply poison bait only once per year. Surviving squirrels from the first treatment sometimes become ill after eating bait. Consequently, these animals will become bait shy and further treatments are unsuccessful. Use of poison baits according to label directions usually results in an 80 to 90 percent reduction in Wyoming ground squirrel numbers. Poor results after baiting usually are due to improperly placed bait, failure to prebait, presence of green vegetation, or inactivity of a portion of the ground squirrel population.
Fumigants Use fumigants when additional control is required.
Aluminum phosphide and gas cartridges are registered for use in Colorado. Trade names for aluminum phosphide include Phostoxin, Gastoxin and Fumitoxin. Aluminum phosphide is classified as a restricted use pesticide and gas cartridges are classified for general use. Fumigants are most effective when used in moist soils in early spring. Aluminum phosphide is classified as a flammable solid.